EnvironmentalGeomorphology ...

inEarth Surface Pro 4

IXLIST OF CONTRIBUTING AUTHORSFor 2.3 and 6.4Mauro MARCHETTIDipartimento di Scienze della Terra, Universita degli Studidi Modena, Largo S. Eufemia, 19, 41100 Modena, ItalyFor 3.2Giuliano RODOLFIDino TORRIDipartimento di Scienza del Suolo e, Nutrizione dellaPianta, Universita degli Studi di Firenze, Piazzale delleCascine, 15, 50144 Firenze, ItalyConsiglio Nazionale delle Ricerche, Centro per la Genesi,Classificazione e Cartografia del Suolo, Piazzale delleCascine, 15, 50144 Firenze, ItalyFor 3.3Alessandro PASUTOMauro SOLDATIConsiglio Nazionale delle Ricerche, I.R.P.I., Bacini Italianordorientale, Corso Stati Uniti, 4, 35020 Camin — Padova,ItalyDipartimento di Scienze della Terra, Universita degli Studidi Modena, Largo S. Eufemia, 19, 41100 Modena, ItalyFor 3.4.2Franca MARAGAConsiglio Nazionale delle Ricerche, I.R.P.I., Bacinopadano., Strada delle Cacce, 73, 10135 Torino, ItalyFor 3.5.2Paolo ORRU andAntonio ULGEZADipartimento di Scienze della Terra, Universita degli Studidi Cagliari, Via Trentino, 51, 09127 Cagliari, ItalyFor 3.6Alberto CARTONDipartimento di Scienze della Terra, Universita degli Studidi Torino, Via Accademia delle Scienze, 5, 10123 Torino,Italy

For 3.7.4Doriano CASTALDINI Dipartimento di Scienze della Terra, Universita degli Studidi Modena, Largo S. Eufemia, 19, 41100 Modena, ItalyFor 4 and 5.4Sandra PIACENTEDipartimento di Scienze della Terra, Universita degli Studidi Modena, Largo S. Eufemia, 19, 41100 Modena, Italy

xiContentsForeword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .List of contributing authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .viiIX1 INTRODUCTION TO ENVIRONMENTAL GEOMORPHOLOGY ..... .1.1 Definition of Geomorphology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Geomorphology and Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Geomorphology as a science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.4 Environmental Geomorphology . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.5 Environmental impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.6 Geomorphological risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 GEOMORPHOLOGICAL RESOURCES . . . . . . . . . . . . . . . . . . . . . . . . . 82.1 Geomorphological raw materials . . . . . . . . . . . . . . . . . . . . . . . . . . 82.1.1 General aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.1.2 Earth materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.1.3 Soil .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . 142.1.4 The contribution of Geomorphology in the search for othernatural resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.1.4.1 Solar radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.1.4.2 Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192.1.4.3 Glaciers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252.1.4.4 Geothermal energy . . . . . . . . . . . . . . . . . . . . . . . . 252.2 Landforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262.3 A method for surveying, mapping and assessing landforms asgeomorphological assets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 GEOMORPHOLOGICAL HAZARDS . . . . . . . . . . . . . . . . . . . . . . . . . . 353.1 Geomorphological instability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353.2 Soil erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363.2.1.1 Definition and terminology . . . . . . . . . . . . . . . . . . . 363.2.2 Physical bases of erosion . . . . . . . . . . . . . . . . . . . . . . . . . . 383.2.2.1 Forces produced by fluids in motion . . . . . . . . . . . . 383.2.2.2 Forces resisting detachment . . . . . . . . . . . . . . . . . . 413.2.3 Water erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423.2.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

xii3.2.3.2 Impact of raindrops . . . . . . . . . . . . . . . . . . . . . . . . 433.2.3.3 Overland flow erosion . . . . . . . . . . . . . . . . . . . . . . 46Flow detachment . . . . . . . . . . . . . . . . . . . . . . . . . . 46Transport capacity of rill flow . . . . . . . . . . . . . . . . 47Rill erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483.2.3.4 Differential erosion . . . . . . . . . . . . . . . . . . . . . . . . 493.2.3.5 Subsuiface flow . . . . . . . . . . . . . . . . . . . . . . . . . . . 493.2.3.6 Gully erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503.2.4 Aeolian erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533.2.5 Models for evaluating water erosion . . . . . . . . . . . . . . . . . . 553.2.5.1 General overview . . . . . . . . . . . . . . . . . . . . . . . . . 553.2.5.2 De Ploey 's erosion susceptibility model . . . . . . . . . . 583.2.5.3 PSIAC model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603.3 Landslide hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643.3.2 Types and causes of landslides . . . . . . . . . . . . . . . . . . . . . . 663.3.2.1 General aspects . . . . . . . . . . . . . . . . . . . . . . . . . . 663.3.2.2 Internal causes . . . . . . . . . . . . . . . . . . . . . . . . . . . 693.3.2.3 External causes . . . . . . . . . . . . . . . . . . . . . . . . . . . 713.3.3 Techniques for landslide investigation . . . . . . . . . . . . . . . . . 723.3.3.1 Retrospective research . . . . . . . . . . . . . . . . . . . . . . 733.3.3.2 Databases and GIS . . . . . . . . . . . . . . . . . . . . . . . . 753.3.3.3 Remote sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . 763.3.3.4 Mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793.3.3.5 Geotechnical investigations and monitoring . . . . . . . 81Methodological aspects . . . . . . . . . . . . . . . . . . . . . 82Sensors and instrumentation . . . . . . . . . . . . . . . . . . 83Monitoring of suiface deformations . . . . . . . . . . . . . 83Monitoring of subsuiface deformations . . . . . . . . . . 84Monitoring of groundwater pressure . . . . . . . . . . . . 85Monitoring of climate (weather) . . . . . . . . . . . . . . . 853.3.4 Landslide hazard assessment . . . . . . . . . . . . . . . . . . . . . . . . 863.4 River hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 883.4.1 River erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 883.4.1.1 Erosion in the strict sense . . . . . . . . . . . . . . . . . . . 893.4.1.2 Cavitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903.4.1.3 Abrasion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903.4.1.4 Degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903 .4.1.5 The action of mountain streams . . . . . . . . . . . . . . . 913.4.2 River instability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 923.4.2.1 General overview . . . . . . . . . . . . . . . . . . . . . . . . . 923.4.2.2 Main channel shaping . . . . . . . . . . . . . . . . . . . . . . 973.4.2.3 Channel pattern mobility . . . . . . . . . . . . . . . . . . . . 983.4.2.4 Channel network adjustment . . . . . . . . . . . . . . . . . . 99

3.4.2.5 Headward erosion .. . ...................... 1013.4.2.6 Tributary junction change . . . . . . . . . . . . . . . . . . . 1023.4.2.7 Flooding ............................... 1033.4.2.8 Inundation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1063.5 Marine hazard ....................................... 1103.5.1 Geomorphology ...... .. ...... ... ................ 1103.5.1.1 Coastal environment . . . . . . . . . . . . . . . . . . . . . . . 1103.5.1.2 Coastal processes ......................... 1123.5.1.3 Cliffs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1133.5.1.4 Beaches ................................ 1153.5 .1.5 The evolution of coastlines . . . . . . . . . . . . . . . . . . . 1183.5.1.6 Continental shelf and slope . . . . . . . . . . . . . . . . . . 1193.5.2 The Hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1203.5.2.1 Coastal hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . 1203.5.2.2 Hazard affecting cliffs ...................... 1213.5.2.3 Hazard affecting beaches . . . . . . . . . . . . . . . . . . . . 1223.5.2.4 Hazard affecting lagoons .................... 1243.5.2.5 Hazard affecting continental shelves . . . . . . . . . . . . 1253.5.2.6 Hazard affecting continental slopes . . . . . . . . . . . . . 1283.6 Glacial and periglacial hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1353.6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1353.6.2 Ice-rock avalanches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1373.6.3 Supraglacial debris fall/slide outside the lateralmoraine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1393.6.4 Ice fall from snout of glaciers (ice avalanches) . . . . . . . . . . . 1413.6.5 Rapid advance of glacier snouts (surges of glaciers) ....... 1433.6.6 Emptying of internal water-pockets, proglaciallakes andice-dammed lakes ............................... 1443.6.7 Highwater events on the valley floor connected with thepresence of glaciers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1483.6.8 Lahars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1493.6.9 Hazards derived from mountain climbing ............... 1493.6.10 Mass falls owing to confluence glaciopressure . . . . . . . . . . . 1503.6.11 Assessment of the hazard derived from the presence ofice masses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1503.6.12 Avalanches ..... . .............................. 1523.6.13 Rock glaciers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1593.6.14 Debris flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1623.6.15 Final remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1643.7 Geomorphology and seismic risk .......................... 1653.7.1 Seismic risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1653.7.2 Morpho-neotectonics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1663.7.3 Geomorphology and seismic susceptibility .............. 1723.7.3.1 Slope angle . ... . ...................... . .. 174xiii

xiv3.7.3.2 Debris ................................. 1743.7.3.3 Morphology ............................. 1753.7.3.4 Degradational slopes .................... . .. 1763.7.3.5 Paleolandslides ........................... 1793.7.3.6 Underground cavities ....................... 1793.7.4 Earthquake-triggered mass movements ................. 1803.7.4.1 Worldwide examples .............. . ... . .... 1803.7.4.2 Examples in Italy ......................... 1813.7.4.3 Study methodologies in Italy .................. 1833.7.4.4 Conclusions ............................. 1853.8 Geomorphology and volcanic hazard . . . . . . . . . . . . . . . . . . . . . . . 1873.9 Geomorphological hazard maps .................... . ...... 1893.9.1 Causes of hazard ................................ 1913.9.2 Effects of hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1933.9.3 Synthesis of survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1944 MAN AS GEOMORPHOLOGICAL AGENT . . . . . . . . . . . . . . . . . . . . . 1974.1 An approach to the problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1974.2 Man's activities and their geomorphological consequences ........ 2004.2.1 General aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2004.2.2 Consequences of hunting .......................... 20 I4.2.3 Consequences of animal-farming ..................... 2014.2.4 Consequences of agriculture .... . ................... 2034.2.5 Consequences of resource exploitation ................. 2054.2.6 Consequences of engineering works ................... 2074.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2095 VULNERABILITY AND GEOMORPHOLOGICAL RISK . . .......... 2145.1 Vulnerability to hazard ................................. 2145.2 Risk mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2165.3 Prediction and forecast ... . ............................. 2185.4 Environmental education ................................ 2196 GEOMORPHOLOGY AND ENVIRONMENTAL IMPACTASSESSMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2236.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2236.2 Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2256.3 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

6.3.1 Types of projects .. .... .... .. . . . .. ............... 2276.3.2 Investigation phases ........ .... .......... .. ...... 2286.3.3 Mapping .. ....................... . ... . .. .. .... 2286.3.4 Indicators .... . ........ . ..................... . . 2296.3.5 Evaluation of Hazards and Assets .................... 2306.3.6 Evaluation of Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2316.3.7 GIS Techniques ......................... . ....... 2326.4 Quantification of impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2336.4.1 Raw materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2336.4.2 Landforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2346.4.3 Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236XV7 CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237REFERENCES ............................................ 240BIOGRAPHY ............................................. 263

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ENVIRONMENTAL GEOMORPHOLOGY1 INTRODUCTION TO ENVIRONMENTAL GEOMORPHOLOGY1.1 Definition of GeomorphologyGeomorphology, from the Greek words yfj jiopcpfi X6joq, is a science which aimsto study and interpret landforms and especially the causes that create and modifythem.Geomorphology's main area of study is the contact surface between thelithosphere, on the one hand, and the atmosphere and/or the hydrosphere, on the otherhand, that is, the interface between two different physical entities: a solid mediumand a liquid and/or aeriform one. It is along this surface that geomorphologicalprocesses take place.Two types of forces are exerted along this interface: endogenetic and exogenetic.The former (internal) originate in the substance of which the Earth is made andproduce changes in the lithosphere. They are diastrophic phenomena giving rise tocrustal deformation, volcanic activity and the slow transfer of the inner heat of theearth to the surface. Exogenetic (external) forces originate in the solar system andmodify the surface of the lithosphere. They are principally the force of gravity andsolar energy, which determine vectorial movements, convection and tangentialmovements of portions of solid, liquid or aeriform masses on the above-mentionedinterface.This scheme of subdivision leads to the distinction between landforms andprocesses caused by internal geodynamics, termed endogenetic, and those landformsand processes that are related to external geodynamics, termed exogenetic. Themorphology of the Earth is a result of the interaction of both forces, with theprevalence of one or the other in terms of space and/or time. Sometimes and in someplaces, volcanic or tectonic phenomena may give the most significant features to theland surface, prevailing over the external processes of erosion or deposition. At othertimes or in other places, the external processes of landscape formation may hide ordestroy reliefs or depressions of endogenetic origin. For example, in volcanic areas,such as Mt. Etna or Mt. Pelee, or in tectonically active areas, like California or insome Mediterranean regions, the internal geodynamic components are evident in theoverall morphological configuration of landscape reliefs. On the other hand, erosionlandforms such as the badlands in Dakota, or a landslide in the Alps, or on the coastof the English Channel more clearly reveal the external features related to the actionof water and the force of gravity in the formation of that particular landscape.

1.2 Geomorphology and GeologyA definition of the areas of investigation specific to Geomorphology compared withthose specific to Geology might at this point be opportune. The criteria for a dividingline may be found in the concept that Geomorphology is concerned with the units onthe Earth's surface that are genetically linked to the relief that can be observed at thepresent time, whereas Geology involves the investigation of other units linked tolandscapes on the Earth, which in that particular area have undergone a radicalchange.Therefore, from the conceptual viewpoint, it is not a chronological criterion thatenables the two fields of study to be distinguished since relief units of the same agemay be features under investigation in both fields of study. For example, morainedeposits of the Gtinz in the Alps come under the heading of geomorphologicalinvestigations, whereas a deposit of the Calabrian, more or less the same age, in theSouthern Apennines would belong to the field of Geology. In fact, the former is theresult of deposition from a glacier that occupied a valley quite similar to the valleyin which the deposit is now located. The latter, on the other hand, is the result ofdeposition in a marine environment, which differs considerably from a subaerial one,where the deposit now outcrops.At any rate, it is clear that the landscapes of the past which are still preserved onthe earth's surface are prevalently the least ancient ones, as the probability of theirundergoing (endogenetic or exogenetic) transformation processes has been reduced.As a result the least ancient units on the earth's surface often prove to be the objectsof geomorphological studies. Therefore, the time frame in which geomorphologicalstudies are concentrated is the Quaternary era (Table 1).It is from this conceptual boundary between Geomorphology and Geology thata difference in the method of scientific investigation is also derived. The geomorphologistmust always seek a logical connection, an explanation, a cause andeffect relationship between a particular outcrop and the surrounding landscape:between the moraine deposits and the valley, a landslide accumulation and the mainscarp, a paleobeach and a marine coast, even if the latter has retreated, etc. On theother hand, the pure geologist relies on outcropping rocks alone, albeit in the contextof surrounding formations, in order to obtain a paleogeographic framework bydrawing on the stratigraphical, sedimentological, paleontological and petrographicalcharacteristics together with other features of the rock. This framework may also beobtained through a palinspastic reconstruction of the original positions of the rocksin that specific moment in geological history to which the outcropping rock typebelongs, before the rocks may have been subjected to any folding or thrusting.1.3 Geomorphology as a scienceIt must be said that Geomorphology is an ''empirical" science. That is, a sciencebased on observation and experience, experimental research on the various processes

TABLE 1Chronological scheme of the QuaternaryB.P. MAGNFnCy. 10^ POLARITYSTRATIGRAPHYGLACIATIONSN.EUROPE1 N.AMERICA^CmOLOGT^B.P.y. 10^P O S T G L A C I A LWEICHSEL ' WISCONSINMagdalenianMousterianCROMAGNONNEANOeRTHALTYRRHENIANSILLINOISYARMOUTHo -^KANSASAFTONGUNZ ! MENAPIIPRE -DONAU PRE-EBURONAusmALOPtmecusand forms of landscape formation, that is, on individual cases chosen among theinfinite variety of geomorphological phenomena, all of which are different. For thisreason, it is impossible to apply a ''systematic" method following the procedures ofother natural sciences such as Zoology or Botany. The adoption of methods of thistype, that is, the conception of Geomorphology as a systematic science usingschematic procedures to explain the genesis and evolution of a physical landscape,can lead, and in certain cases has unfortunately led, to misconceptions and a fossilisationof research, by weighing it down with rigid preconceived models and patterns.Should it become necessary to adopt models, they should either refer to specificexamples or be obtained from cases that have been directly observed. In this way,they are given no genetic significance but may be used for descriptive and illustrativepurposes. Other models may be of theoretical value alone and present an intentionallylimited number of variables selected from the infinite number of variables that playa part in the evolution of geomorphological phenomena. For this reason, the solepurpose of such models is to define the role of these variables, considered individuallyor in connection with others. However, they should never be taken as rules forindicating specific aspects of morphogenesis.For the same reasons, it is not possible to "classify" either geomorphologicalprocesses or the landforms they create. In other words, they cannot be subdivided intospecific "classes" like plants, animals, minerals, etc. They may instead be split into

and on the development and activities of living organisms". It is therefore used in anecological sense.The geomorphological components may be schematically subdivided into:— geomorphological resources; and— geomorphological hazards.Geomorphological resources include both raw materials (related to geomorphologicalprocesses) and landforms — both of which are useful to man or may become usefuldepending on economic, social and technological circumstances. For instance, littoraldeposits can become important, economically valuable and considered as geomorphologicalresources when used for sand quarrying. Similarly a sea beach canacquire value and considered as a geomorphological resource when utilised as aseaside resort.Geomorphological hazards can be defined as the "probability that a certainphenomenon of geomorphological instability and of a given magnitude may occur ina certain territory in a given period of time". For example, in any one area, thepossibility of a certain landslide occurring over a 50-year time span may be assessed.In the context of relationships with the environment, man represents:— Human activity; and— Area vulnerability.Human activity is the specific action of man which may be summarised under theheadings of hunting, grazing, farming, deforestation, utilisation of natural resourcesand engineering works.Area vulnerability is the complex of all things that exist as a result of theintervention of man in a given area and which may be directly or indirectly sensitiveto material damage. Included in this complex, we find the population, buildings andstructures, infrastructures, economic activity, social organisation and any expansionand development programs planned for an area.Considering the relationships between Geomorphological Environment and Man,two main possibilities can be examined (Panizza, 1992) (Fig. 1):passiveGeomorphologicalEnvironmentactivt^ fGeomorphologicalResourcesy fIMPACTai•the ,^^^^M ^ ^ /?fl-^-^

a) Geomorphological Resources in relation to Human Activity, where the GeomorphologicalEnvironment is regarded as mainly passive in relation to Man (active).In other words, a resource may be altered or destroyed by human activity (e.g.,a mountain landscape that has been modified by a bulldozer).b) Geomorphological Hazards in relation to Area Vulnerability, where theGeomorphological Environment is regarded as mainly active in relation to Man(passive). In other words, a hazard may alter or destroy some buildings orinfrastructures (e.g., a landslide or river erosion that causes road collapse).To conclude this conceptual outline, we can define as IMPACT the consequences ofHuman Activity on a Geomorphological Resource and as RISK the consequences ofGeomorphological Hazards on a situation of Area Vulnerability (Fig. 2).1.5 Environmental impact"Environmental Impact", as it will be considered here, consists in the physical,biological and social changes that a human intervention brings about in theenvironment, the latter term being intended in its geomorphological elements.Therefore, impact equals the "product" of man's activity and geomorphologicalresources.:^^:s'^-^^%:i/--^

Raw materials related to geomorphological processes are generally nonrenewable,at least not on a time scale comparable to the history of man. However plentiful thereserves may be, a rapid rate of consumption, as there has been in the recent yearsof our history, may lead to irreversible depletion. In addition, the uncontrolledutilisation of some materials, such as alluvial gravels from riverbeds, can lead to anegative impact not only in the area that is more or less directly involved, that is, theriverbed or the surrounding slopes, but also in locations that may be distant from thegravel pit, for example along the coast near the river mouth, with negative effectsnoticeable only after a certain length of time.Moreover, there are sites or landforms of great value in terms of scientificheritage. The assessment of this value is based on their rarity, critical position in thefoundation of an ecosystem, basic scenic appeal, paleoheritage, etc. Some systemshave a high educational value as they facilitate an approach to knowledge about theenvironment and encourage environmental awareness. Children and adults alike needto be informed about the environment if they are to manage, understand and supportmanagement activity in the future. To do this, the examples useful for educationalpurposes must be protected and safe; sensible access to them should also be provided.Impact may be assessed in terms of:a) magnitude, which consists of the quantifiable entity of the changes;b) the sign, that might be positive or negative;c) the extension, referring to the area involved;d) the duration, which refers to the persistence of the changes over time;e) the moment in which the impact occurred;f) the probability of its occurring;g) reversibility, that is, the possibility that the environmental situation may return topreimpact conditions;h) synergistic impact situations; andi) mitigation, that is, the possibility of mitigating effects, etc.It should be mentioned here that this type of impact is not entirely identical to theone found in the "Environmental Impact Assessment" standards/regulations, whichwill be discussed later.1.6 Geomorphological risk"Geomorphological Risk" is a natural risk connected to a geomorphological hazard:the term refers to the probability that the economic and social consequences of aparticular phenomenon reflecting geomorphological instability will exceed a certainthreshold (Panizza, 1987). Therefore, "geomorphological" risk is equal to the "product"of geomorphological hazard and an area's social and economic vulnerability.Vulnerability refers particularly to an area's population, buildings and itseconomic and social infrastructures. Thus, the assessment of risk must necessarilyinclude an analysis of all the man-made structures existing in a given area and takeinto consideration the extent to which the existing situation is vulnerable with regard

to a given geomorphological event (exposure and vulnerability). For example, landslidingis a hazard that may not involve any risk in a desert area, whereas in adensely populated or highly industrialised area, it may represent a high risk. However,the assessment of risk must also include the prospect of new buildings andinfrastructures (planning and vulnerability). Therefore, an accurate investigation ofa territory's geomorphological stability is indispensable before applying engineeringsolutions. Vulnerability is also related to the existing degree of preparedness andsocial organisation, i.e., environmental education, civil defence and prediction andmonitoring techniques. In areas where the population is aware of the problem andsafeguards its territory, where the boards responsible for intervention are efficient,where advanced warning systems exist for major instabilities (e.g., river high-waters,storms in coastal areas, etc.) and finally, where such a high level of social organisationexists, the levels of vulnerability are certain to be lower.As for "geomorphological" risk mitigation, intervention is possible against boththe hazard and vulnerability. For example, in the case of a building that has beenbuilt or is scheduled for construction on a degraded slope affected by solifluction, itis possible to intervene with land upgrading works (against hazard) or with deepbuilding foundations (against vulnerability). In the case of lateral river erosion, it ispossible to implement hazard mitigation through diversions or rectifications of theflow (channelization) or through a reduction of its energy (dykes). Banks could alsobe reinforced and vulnerability thereby reduced. Nevertheless, in many of the mosthazardous cases, such as large landslides, mitigation of the hazard is the onlyintervention possible (see 5.2).Therefore, mitigation of geomorphological risk must come to terms with aspect,planning and organisation problems, i.e., problems of a social and economic nature,as well as those associated with political administration. In fact, risk mitigationoperations of a preventative nature, involve an evaluation of costs and benefits. Someguarantees and levels of protection must be determined for both man and theenvironment. In some cases a risk threshold will have to be established and the higherit is, the more onerous and expensive it will be. In other cases, a priority scale willhave to be defined concerning the various environmental risks or a choice will haveto be made between risk mitigation and other programmes.2 GEOMORPHOLOGICAL RESOURCES2.1 Geomorphological raw materials2.1.1 General aspectsBefore discussing this subject in detail, it is useful to define three different terms thatare commonly used as synonyms. They are raw materials, resources, and reserves.

In a literal sense, a raw material is intended as any element of a natural systemwhich can be utilised for processing. In everyday language, only some of the basicsubstances used in industry are indicated with this word (e.g., coal, oil, rock, mineraland metal ore, chemical substance, etc.) and likewise those farming products used onan industrial scale (e.g., rubber, wool, cotton, silk, timber, etc.) since they are all rawmaterials for a large number of producers.On the other hand, the meaning of resource is derived from a cultural concept:a raw material is transformed into a resource when utilised by man under particularsocial, economic and technical conditions. Therefore, the transformation of a rawmaterial into a resource is a reversible process. In fact, when a resource ceases to benecessary, it again becomes a raw material, with no particular value. This is whathappened to the flintstone that was a resource of paramount importance throughoutthe Neolithic period, but became a raw material once more when the mines were nolonger used. Resources as such are therefore determined according to the humanconcept of usefulness and, as a consequence, their value changes according tovariations in social, economic and technological conditions.Reserves correspond to the resources that are actually available under present daysocioeconomic and technological conditions: they are therefore the most specific butalso the rarest of the three categories afore mentioned and assume a particular valueonly in a limited period of time: the present.If raw materials are valuable, they can be called assets: therefore if geomorphologicalraw materials are valuable, they can be called geomorphological assetswhich, in turn, may be considered, and really become, geomorphological resourceswhen used by man (Fig. 3).In order to be consistent with the general aims of this book, which deals withgeomorphological matters, the specific themes concerning the search and exploitationof natural resources will not be discussed here nor will the economic problems linkedto them, but after a general review a detailed discussion of the relationships betweensome kinds of resources and Geomorphology will be presented.However, it is obvious that activities connected with the use of raw materials caninterfere with other aspects of the territory resulting in environmental risk and impact.For example, in the geomorphological field, a rock quarry could:a) modify environmental characteristics such as a slope shape;b) destroy cultural assets such as a glacial cirque or a paleocliff;c) cause environmental risks such as a landslide on communication lines.At the same time, of course, everything concerning the use of natural resources hassocial and economic implications.Raw materials, in particular those that make up natural resources utilised by man,are generally subdivided into two categories:— Renewable. They are theoretically inexhaustible since they are found in very largeGEOMORPHOLOGICAL ^GEOMORPHOLOGICAL ^ GEOMORPHOLOGICALRAW MATERIALS if valuable ASSETS ~V^ RESOURCESFig. 3. Relationships between geomorphological raw materials, assets and resources.

10quantities or are periodically renewed or reproduced. In this category variouskinds of energy sources are included, such as geothermic or solar energy, waves,wind and flowing waters, farming and forestry land and fishing products.Nevertheless, some of these could be destroyed or made nonrenewable as aconsequence of man's actions: i.e., some farming territories in the Americas weretransformed into irrecuperable wasteland by the speculative greed of the firstEuropean settlers.— Nonrenewable. They are on the contrary those subject to depletion since they arepresent in limited quantities and are not renewable on the same time scale asman's history. They are mineral ore, fossil coal, building materials, natural gasand oil. Although the reserves of these materials may be plentiful, a rapid rate ofconsumption, as has occurred in recent decades, could lead to their irreversibledepletion.A progressive substitution of renewable resources by nonrenewable ones has beentaking place during the past decades: farming activities once performed only with theaid of domestic animals now require the use of fossil fuels; natural fertilizers havebeen replaced by those derived from natural gas; containers once made of wood arenowadays made of plastic which, in turn, derives from crude oil. Moreover, theconstant dwindling of available natural resources leads to the progressive exploitationof other resources containing smaller amounts of useful substances, whose utilisationleads to increased energy consumption and therefore to a further use of nonrenewableraw materials.Another problem to be taken into account is the degradation of the environmentresulting from the excessive consumption of nonrenewable resources, for example,pollution problems caused by the use of chemical fertilizers and pesticides, or by theexhaust fumes from motor vehicles and emissions from heating plants using keroseneor natural gas. Other problems are created by the accumulation of refuse of industrialorigin such as scrapped cars, electric appliances, plastic containers, mineral productsdiscarded after extraction and refinery processing and radioactive waste. Thetreatment and disposal of urban and industrial waste is causing a hazardous declinein the quality of air, soil and water, as well as biological damage to plants andanimals.Environmental alterations lead to changes or destruction of the ecosystems, whilethe possibilities of recreating renewable resources are progressively reduced: anemblematic example is given by the sea, where fishing resources are undergoing aconstant decline owing to water pollution.The consequences of technological innovation, progressive industrialisation andurbanisation, rapid changes in the social systems and economic growth, are alsoaccompanied by a strong population increase demanding an ever growing need ofnonrenewable raw materials. This means there is a danger of a complete depletionand a change in ecological cycles, with the risk of hindering the reproduction ofrenewable resources. The situation is growing more and more serious and is leadingto limits of survival close to a general catastrophe.The tendency towards an ever increasing shortage of these natural resources.

which are often used inadequately together with environmental degradation, can befought only by a rational policy of territorial planning. There should be twofundamental parallel actions: conservation and innovation, which determine a morebalanced management of natural resources and of the environment. This would aimto reduce consumption and artificially induced needs, privileging instead ways of liferequiring lower levels of energy. At the same time, the technologies based onminimum waste production should be adopted, with the possibility of recycling refuseand reducing the built-in obsolescence of many products.The future availability of resources depends mainly on these two actions.Conservation must be part of a concerted effort to safeguard the landscape by meansof a better knowledge of the environment around us. As for innovation, technologicalprogress could delay the depletion of nonrenewable raw materials by shifting forwardin time the limits imposed by Nature, for example, by improving the productivity ofrenewable resources.Finally, a more effective commitment to the research on alternative energy isnecessary, in particular solar energy since it may be the only one capable of givinga safe and durable solution to the problem of energy resources.2.1.2 Earth materialsMetallic and nonmetallic minerals, fossil fuels and building materials are all includedin the category of nonrenewable resources.Geomorphological processes and conditions can be more or less related to theorigin, position, state of conservation and exploitation of these materials. Thereforethe appUcations of Geomorphology also play a part in this picture. The relationshipsbetween the most widespread categories of these resources and the Earth's reliefs canbe summarised as follows (see Demek, ed., 1972; Cooke and Doornkamp, 1974; withmodifications):a) Resources directly connected with the relief:— building materials derived from competent and incompetent rocks alike(marble, granite, clay, sand, gravel, etc.);— clastic mineral ores (gold, diamonds, heavy minerals, etc.);— alteration mineral products (kaolin, limonite, bauxite, etc.);— basin mineral deposits (coal, peat, etc.).b) Resources indirectly connected with the relief; for example those associated withtectonic morpho-structures, such as gas and mineral oil, rock-salt, coal, etc.c) Resources not connected with the relief, such as deep metalliferous or nonconcentratedmineral ore deposits.Among mineral ore deposits, a further subdivision can be based on their genesis:eluvial, colluvial, alluvial, etc.The relationships between the Earth's reliefs and natural resources have beenshown in order to emphasize the contribution of Geomorphology also in this field ofEarth Sciences, in particular by means of geomorphological survey and mapping.These investigations might seem obvious considering their relations with clastic11

12deposits (e.g., glacio-fluvial sands or eolian silts) or with particular environmentalimplications (e.g., peat deposits or bauxite ore). Nevertheless, they are essential alsoin many other less immediately evident situations: morpho-structural and morphoneotectonicinvestigations are particularly useful for the search of minerals related totectonic phenomena. Moreover, for those situations caused by successive weatheringprocesses, rillwash, enrichment and deposition, a reconstruction of the geomorphologicalevolution of the area is indispensable.Earth materials more directly related to Geomorphology are sand and gravel.According to their origin, they can be subdivided as follows:— alluvial deposits;— marine-coastal deposits;— slope deposits;— glacial deposits.These kinds of Earth materials are sought after for the production of concrete, for theconstruction of road and railway beds, for macadam and ballast preparation, etc. Butnot all sands and gravels are suitable for these purposes: detritus derived from verybrittle rocks should be excluded owing both to the intrinsic nature of the rock (e.g.,gypsum) and to the weathering processes. Equally important are: the sort of material,the thickness of the deposit, the nature and distribution of available resources, theroundness of rock particles, etc. In order to know and properly assess all thesecharacteristics it is necessary to carry out detailed geomorphological survey andmapping, as well as relying on in situ and laboratory measurements.For example, the composition of fluvial gravel will correspond to the lithologicalcharacteristics of the river's catchment basin upstream of the extraction area. Fromthe examination of the geomorphological map it will be possible not only to deducethe general lithological character of the deposit but also the approximate percentageof the different kinds of rocks that constitute it, on the basis of the wideness of theoutcrops and of their resistance to weathering. If the deposits are terraced, thematerial is often weathered and the thicker the alteration layer, the older the terraceand the higher its position compared with the present valley floor (Fig. 4). The searchfor gravel in these cases should be directed towards the lower terraces, consideringin particular the foot of the terrace, where unweathered gravel deposits are moreUkely to be found. Moreover, from geomorphological maps and more detailed fieldsurveys it will be possible to estimate the thickness and therefore the volume ofexploitable gravels. In situ and laboratory analyses will also provide lithological andparticle-size information.Similar considerations can be made for other kinds of deposits, such as morainicones, although they are usually characterised by a certain amount of silt and claywhich may reduce the materials' field of application and should therefore be removedbefore being used.The use of talus as a raw material depends on its lithological composition, itsstate of weathering and also its final purpose: it can generally be utilised for roadbeds, even when altered. Instead, for some constructions, such as retaining dams, thematerial must be very fresh.

13Fig. 4. Alluvial terrace deposits near the Seche Torrent in Martinique. Notice the tyres incorporated withinsands and gravels at the base of a deposit over 20 m thick: these singular "fossils" show an extremelyrecent age of the terrace deposits (photo M. Panizza, March 1994).When a project of exploitation of a raw material is activated, it is indispensableto assess its consequences, especially in terms of environmental impact. For example,quarrying activities of slope deposits can cause mass movements in the adjacentslopes. Tips of waste materials create artificial scarps with negative consequences notonly for the landscape but also for geomorphological stability.An example of irreversible environmental damage is given by the consequencesof quarrying along and within riverbeds.The removal of gravel and sand from riverbeds can trigger a series of differentconsequences both in the short and long term. First of all, the lowering of theriverbed due to excavation causes an increase of the watercourse's profile acclivityupstream of the excavation area, thus augmenting the flow velocity and the erosivepower of the water. The removal of alluvial deposits from riverbeds exposes thesubstratum to erosion, especially if it is made up of cohesionless or pelitic rocks, andcauses a deepening of the runoff channels. Along erosion furrows the river's waterattains a higher velocity that it would have in a wide riverbed and therefore itincreases its erosive power. Such erosion phenomena can determine the drainage anddepletion of the more superficial aquifers as well as the destruction of the underdrainageflow.Moreover, downstream of the quarrying area fluvial waters might carry a smallerload of coarse materials, compared with the period prior to the removal of riverbed

14deposits, and a higher content of finer suspension elements deriving from the erosionof a peHtic substratum. As a consequence, in the lower plain the deposition ofabnormal amounts of fine sediments could take place, leading to a raising ofriverbeds already suspended in some stretches of their course and therefore to agreater flooding hazard. Less coarse material will also be deposited at the river'soutlet and along the adjacent seashores whilst silty-clayey sediments not previouslydispersed and deposited during floods will prevail in some coastal areas. A lack ofcoarse deposits causes a decrease of supply for the beaches, which are consequentlymore subject to regression and erosion.The above-described phenomena have occurred in several cases, following intensequarrying in the beds of many watercourses of northern and central Italy, the effectsof which may be seen along the Romagna and Marche Adriatic coast.From the above-mentioned cases, it appears clear that the negative effects ofquarrying do not only concern the territory directly affected by the exploitationactivities of a natural resource, such as a riverbed or a mountain slope, but can havefurther repercussions on the environment, even in areas far from the quarry and aftera considerable length of time has elapsed.2.1.3 SoilSoil is a natural resource since it is the essential element in agriculture and is closelyrelated to the geomorphological evolution of the site where it has been formed.A soil can be considered as a thin layer that coats the dry land at the interfacebetween lithosphere and biosphere, surrounded by water, ice and rock outcrops. Soilis created by the transformation undergone by rocks from the moment they appear onthe Earth's surface, in a very different physical and chemical environment from theone where they originated. These transformations occur in different ways in thevarious regions of the planet, according to processes governed by environmentalfactors which impart specific characteristics to the pedological covers. Soils varyaccording to geographical regions and geomorphological environments; they aretherefore an essential component of the landscape and are subject to the same lawsthat control the Earth's modelling. For these reasons the study of soils cannot beseparated from the study of the landforms on which they lie. One could say that thetwo processes of morphogenesis and pedogenesis are inversely proportioned: in facterosional and depositional processes hinder or prevent the soil's formation. On theother hand, pedogenesis could develop where an adequate vegetation cover reducesor prevents soil mobilisation phenomena, i.e., the morphogenetic processes.The study of soils has important practical implications since food resourceslargely depend on their state of health. Notwithstanding this, every year largeextensions of soil are destroyed by the advancing of deserts in tropical regions, byhydraulic and geological disruption and by uncontrolled development of urban andindustrial areas. Soil must therefore be considered as a resource worthy of conservation,on which further advanced scientific knowledge must be acquired.Soil also keeps a historical record: the geological events of the Pleistocene and

the succession of man's cultures during the Holocene have given it recognizablecharacters that allow a proper reconstruction of the environmental changes and maninducedimpact of the past.Soil behaves like an open physicochemical system, with constant matterexchanges with the surrounding systems and transformations within it (Fig. 5). Theenergy necessary for these processes to take place is derived from the Sun's radiantenergy, from the Earth's endogenetic heat, from physicochemical reactions and fromgravity. They all take place through processes that lead to progressive mineralisationof the coarse organic substance provided by the biosphere, the breakdown of mineralmatter at an ionic level, the production of carbonates, silicates and neogenesis oxidesand hydroxides, the transformation of already existing materials and the redistributionof all components. This complex sequence of processes imparts a series of proper,specific characters to the soil that differentiate it from the underlying bedrock.Pedogenetic processes and therefore the soil's characteristics are conditioned byseveral environmental factors which are usually expressed as a function of the15ADDITIONSprecipitation (with ionsand solid particles),organic matterSURFACE6^TRANSFORMATIONS: ,organic matter • humusr£—•hydroxidesprimary mineralsTRANSFERSHumic compoundsclaysions, H4S!04/-^''^^^\TRANSFERSions, H4Si04LOSSESions, H4Si04Fig. 5. Scheme of the main processes acting in soil evolution (after Cremaschi, in Panizza, 1988).

16geographical region, the substratum and the topographical features. The five mainfactors that can be related to the development of a soil are identified by Jenny's(1941) well-known equation:s = f(cl, o, r, /7, f, ...),where;— s corresponds to the soil's properties;— cl is the climate;— o is given by the organisms, including man's activities;— r is the relief and therefore the topographical factor;— p is the bedrock; and— t is time.As they are not included within the aims of this volume, the various factorsregulating pedogenesis will not be discussed in detail nor will the soil's charactersbe classified. Similarly, the problems of paleosoils will not be considered: all theseaspects are dealt with in specific Pedology textbooks.2.1.4 The contribution of Geomorphology in the search for other natural resourcesGeomorphology can offer numerous contributions to the research and exploitation ofnatural resources: field survey and geomorphological mapping; remote sensing;elaboration of special morpho-neotectonic maps; investigations for recognizingcharacteristic relief landforms or features which help in localizing and exploitingparticular resources; collaborations with interdisciplinary investigations; studies forthe reclamation of exploited areas. Some examples are described below.2.1.4.1 Solar radiationThe Earth intercepts part of the energy radiated by the Sun and uses it as its mainnatural resource. The importance of this energy input is due not only to the fact thatwithout it no vegetable or animal life would be possible on the Earth, but alsobecause it is the engine of all the physical phenomena that take place in theatmosphere and of most of those occurring on the Earth's surface: the circulation ofair, the whole hydrological cycle, the movement of ocean currents, the breaking upof rocks, as well as many others.Solar radiation is here considered in its role as a natural resource: one of the mostimportant of its various effects is the generation and support of vegetable life: it istherefore an essential element since it conditions the formation of farming andforestry land.One of the main variables that influence the distribution of the Sun's incident rayson a slope at a certain latitude is slope aspect. Apart from plain areas, it is obviousthat in the northern hemisphere southward slopes are those that most benefit fromsolar radiation: let's consider, for example, the vineyard and orchard-covered hills ofthe preAlpine area in Italy. Aspect has also conditioned the different distribution of

the forests: in many East-West stretching Alpine valleys the North-facing slopes areusually covered by woods while the South-facing ones are utilised for farming andgrazing, since the aforementioned geographical conditions are more suitable for theseactivities.It is, therefore, important to collect adequate information on the morphologicalaspect of slopes. These data will be used not only for forestry-farming purposes butalso for other applications connected with the selectivity of geomorphologicalprocesses such as the wind influence, evapo-transpiration, snow melt, etc., withrelation to the different orientation of slopes.These characteristics can be represented by means of a thematic map of slopeaspect which is one of the specific objects of research and elaboration of quantitativeGeomorphology.For the drawing up of this map a certain number of classes (generally eight)having equal angular magnitude (45°) are chosen. Their central values correspond tothe main cardinal points and to the intermediate ones (North, North-East, East, South-East, South, South-West, West, North-West). Figure 6 shows the eight classes ofaspect and their relative angular values. Plain areas of course cannot have a definedorientation; for this reason a ninth class is represented for surfaces with anacchvity of less than 5%. Each of the nine classes is defined by using differentsymbols. Moreover, the convergence points of the contour lines, corresponding to17M337^30• ^ ^^ VS^S^S^JrVxjc^N ,,30't^N292° 30" / ^^^111111\ ^^" *^^ 1iTTTTv»^247*' 30'. .; •'" v®•% ^ ^ ^C\J "Nj^202° 30'sr°30'ESurfaces with slope angle < 5%Fig. 6. Legend for a map of slope aspect.

18the relief tops and depressions and areas where orientation is undefined since thetangent plane is horizontal, are usually emphasized by means of symbols such as littlecircles.An application of a cartographical elaboration of this kind for farming purposesis given by Tozsa, Molnar and Pelle (1985). The area considered is that of Mt. Somloin Hungary, an isolated hill in a plain area, 432 m above sea level, made up of basaltrocks and cultivated with vineyards. The investigation methods here applied consistin the superimposition of the ''map of slope aspect" (Fig. 7) with a slope angle map(Fig. 8) of the same territory. In the case of Mt. Somlo, the area was subdivided intofive slope angle categories, which make up the usual slope classes in agriculturalapplications in Hungary. The result is a map of solar energy distribution, subdividedinto: 8 X 4 + 1 = 33 categories (Fig. 9). It is possible to calculate the theoreticalquantity of energy that each category can receive during a year for a given region andtherefore correctly assign farming crops on the basis of the minimum energy neededby each vegetable species.Therefore, the "map of slope aspect" is a fundamental document for theevaluation of the energy resource derived from solar energy, with particularapplications in the field of farming land. It is also used in other sectors of appliedGeomorphology, such as the representation of phenomena linked to wind, avalanches,etc.|N FFfflNE^E ^SE[TII]S C^^SwflMlw ^NW[:;^

19

2061kmtSlope angle1 < 5%5-12%13-17%18-25%' > 25%tlat ,1-———-2101826NE-3111927EXPOSUREE-4122028SE-5132129S-6142230SW—7152331W—8162432NW—9172533Fig. 9. Solar energy distribution map of Mt. Somlo, Hungary (modified after Tozsa et al., 1985).implies a certain variety of geomorphological applications, connotations andconsequences. In this section the duties of the geomorphologist will be discussed

when a reservoir construction site has to be chosen giving particular attention to theidentification of the most suitable place for the dam's foundation.When planning a dam, an essential instrument of data acquisition is offered bythe "geomorphological map". Indeed, this descriptive document of the reliefs genesisand the dynamic processes affecting slopes and hydrological networks can show someof the points essential for a satisfactory outcome of the work and its economicviability.When a territory is going to be chosen for a storage reservoir, whether it is forhydroelectric or other purposes, two fundamental characteristics should be identified:a) it should be wide enough; and b) it should not show incompatible processes ofdegradation. Unfortunately in most cases these two conditions appear to beantithetical, since a valley is usually very wide and smooth when degradationprocesses are particularly intense.In any case one of the first evaluations should concern the amount and trend ofthe degradation processes, in order to assess their compatibility with the constructionof the dam. A rapid silting of the reservoir would in fact shorten its existence sinceits economic viability depends on the amount of energy (or other kind of resource)that it can provide and also on its efficient durability in time. Such a disadvantagecould indeed preclude the reservoir's construction unless adequate prevention worksare carried out first.These works should be based on studies which identify the debris' provenance,its trend of transport, its particle size characteristics and its input rate. Geomorphologicalsurvey and mapping could perform most of these duties.First of all, along the mountain slopes the areas most subject to degradationshould be recognised, since they provide most of the detrital materials. Thelithological characteristics of these areas will be examined in detail, with particularattention given to superficial and weathering deposits, their thickness, rate of cohesionand particle size distribution. The degradation mechanisms should also be recognised,whether they are physical or chemical, for example due to frost cracking orhydrolythic alteration: the identification of the causes will lead to the choice of themost appropriate and effective remedial measures. The routes run by the debris toreach the hypothetical basin will be determined and by measuring the solid transportand the amount of rillwash processes, the rate of sheet-erosion will also be calculated.All this is part of the information that geomorphological maps and derivedthematic maps can provide about the problems of active degradation. Thesegeomorphological data will determine the choice of the remedies directed to adecrease of the erosion processes, in order to reduce the silting up of the reservoir.Particularly favourable situations for the choice of a reservoir site are given byglacial landforms such as overdeepened hollows, which can be found along valleyspreviously occupied by Pleistocene glaciers. Moreover, in some places these hollowsare partially dammed downstream by rock-bars which can be the ideal site for thedam's foundation.Apart from being sufficiently wide, the valley which has to be chosen for thereservoir should also be characterised by low acclivity in order to permit the21

22construction of a retaining dam which is not too high.Also a lateral valley, suspended above the main one, in a geomorphologicalcontext derived from ancient glacial modelling, could be a very favourable site,considering also the high vertical interval at the confluence: the dam's constructionin this point could rely also on the noticeable water gradient.Another favourable situation could be found in an area where there had been alake in the past: this would indicate the imperviousness of the ancient basin.Nevertheless, it would be necessary to carry out a detailed geomorphologicalreconstruction of the area and discover the causes that had led first to the lakeformation and afterwards to its extinction, considering particular events that couldhave given rise to cavities or joints, thus increasing the basin's permeability.It would also be essential to investigate slope stability assessment, payingparticular attention to active, potential, quiescent and ancient mass movements.Reference should be made here to the huge landslide that affected the storagereservoir created by the Vaiont dam (district of Belluno, Italy): this vast rock blockand debris slide occurred on 9 October 1963, claiming over 2,000 lives (Fig. 10).Another process to be taken into account concerns the degradation and gravityphenomena along the lake shores: this is a consequence of the artificial reservoirformation and is the effect of vertical variations of the waves' hitting lines and tomoisturization and exsiccation alternations, as a result of water level fluctuations.These settlements are a function not only of the water dynamics but also of thematerial's cohesion and rate of permeability and of the acclivity of the surface inFig. 10. The Vaiont landslide: in the background Mt. Toe with its detachment scarp, in the centre thelandslide heap fallen into the reservoir and in the foreground the dam which withstood the tremendousthrust (photo M. Panizza, June 1990).

contact with the reservoir's water. Once the reservoir's maximum level has beenestablished, detailed investigations will have to be carried out on the characteristicsof the materials that make up the shores of the future storage basin and, as far asGeomorphology is concerned, accurate morphometric measurements of the slopes willhave to be made.Finally, another phenomenon should be mentioned: avalanches. They can haveconsiderable consequences on the silting up of the reservoir, with hazards analogousto those induced by landslides.Even the choice of the site of the foundation requires the geomorphologist'sexpertise. A sufficiently narrow valley section will have to be recognised, confininga territory with the above mentioned requisites and capable of storing the greatestpossible amount of water with the minimum economic commitments. It will have toassure indispensable stability and imperviousness requirements. Particular attentionwill also be given to karst landforms and processes.With reference to what has already been said about reservoirs, a favourablecondition could also be given by a rock-bar along a valley once occupied byPleistocene glaciers, or by a fluvial gorge in correspondence with particularlycompetent rocks. In any case, the choice should be directed towards those riverstretches where a valley goes narrower, downstream of a wide and open sector.Investigations which require the contributions of Geomorphology are thoseconcerning the nature of the dam's threshold, regarding its stability and imperviousnessand more general observations on the territory's evolution, such as theidentification of paleolandslides, that could be decisive for the choice of the damsiteor the most suitable engineering works for the construction phase.One of the first investigations to be performed is a detailed geomorphologicalsurvey of the area where the dam is to be built: the research will aim at recognizinga) the rock-types, as well as their level, kind and grade of weathering; and b) theextent of the degradation processes along the slopes. Undoubtedly the idealcharacteristics would be those corresponding to compact, impervious, non fractured,unweathered rocks, either unstratified, or with bedding and schistosity surfacesdipping upstream. Nevertheless, for certain kinds of dams, such as earth or stone-fillergravity dams or for small irrigation impoundments, a barrier threshold made up ofsuperficial deposits could be suitable. Usually, deposits such as moraine arcs,landslide heaps and talus cones could assure appropriate geotechnical and hydrogeologicalcharacteristics or permit their optimisation by means of opportuneengineering techniques.An important geomorphological problem is given by the presence of buriedriverbeds, i.e., fossil fluvial forms hidden by superficial deposits. A well known andcharacteristic example is that of the epigenetic superimposition of the Avisiowatercourse near the Camini gorge (Trento), illustrated by G.A. Venzo (1957) duringthe geological investigations on the site of the San Floriano d'Egna hydroelectricplant.The reconstruction of the valley's geomorphological evolution, starting from theRiss glaciation up to the present, led to the identification of a buried paleochannel23

24and to the construction of the reservoir in a particularly complex situation.Figure 11, taken from the above quoted article by Venzo, schematically shows thegeomorphological features of the Avisio valley and the hydraulic plant built for theconstruction of the storage reservoir. At the end of the Riss glaciation the valley floorstood at an altitude of about 720 m. At the beginning of the Riss-Wurm Interglacialperiod, the watercourse further deepened its bed, subsequently depositing vastamounts of alluvial sediments up to a height of about 900 m by the end of thatperiod. During the following advance of Wtirmian glaciers, some of these depositswere partially removed and substituted by moraine deposits. The Holocene900 mRiss - WQrmAfter the wormianglacier retreatActual100 200 mFig. 11. Stages in the geomorphological evolution of the Avisio valley (Province of Trento, NE Italy) atForra dei Camini and plan of the damming works carried out (after G.A. Venzo, 1957). Legend: al - Riss-Wiirm alluvial deposits; mo = Wiirm moraine deposits; p = porphyries (bed rock); D = arch-dome dam;/ = diaphragm grouted into the alluvial deposits; R = coating in bentonite-enriched earth; S = cementgroutings in the rock.

watercourse redissected its own riverbed near the Camini gorge. But its courseunderwent a lateral shift, compared with the main axis of the old valley bottom, witha characteristic superimposition phenomenon, and deeply eroded the porphyries onthe right hand side of the valley into ravines. In order to build the reservoir, it wouldnot have been sufficient to dam the Camini ravine, since the water would have runoff through the paleochannel filled with alluvial deposits. Therefore, beforeimpounding the basin, it was necessary to make these sediments impermeable.Treacherous situations could be determined by the apparent presence of bedrockin correspondence with the barrier foundation: it is not uncommon in fact for theaccumulations of rock-block slides to be misinterpreted as bedrock, since they showseveral analogies with primary rock outcrops on their outer surface. The same canhappen with large rock bodies displaced from overhanging slopes and accumulatedfrom falls or slides. Detailed geomorphological surveys can then detect thesesituations, which are not infrequent in the Alpine regions.Among the situations above described, a typical case would be a wide area thatbecomes narrower downstream, at the confluence of different catchment basins,forming gorges or ravines. Moreover, sites like these can offer a particularly suitableplace for the choice both of the storage reservoir (confluence of several valleys) andof the dam foundation (valley narrows). However, particular kinds of landslidebarriers, not rare in the areas affected by Pleistocene glacier advances, have beeninterpreted by the writer (Panizza, 1973) as due to confluence "glaciopressure" (see:3.6.10).2.1.4.3 GlaciersThe use of glaciers as a natural resource has been a well known practice since remotetimes: both for agricultural purposes, with irrigation canals taking their water froma glacier, and as a source of cold for storing food and cooling drinks before theadvent of refrigerators.Water from glaciers is used for the supply of hydroelectric storage reservoirs. Thepresence of glaciers provides a constant supply of waters and therefore an optimalperformance of hydroelectric plants. This is true in particular in the Alpine regions,where summers are usually dry and warm, with hydrological regimes determined byrain and snow feeding in the winter and snow and ice melt-water in the summer.2.1.4.4 Geothermal energyThe inner heat of the Earth, generated and stored underground, makes up a veryrelevant energy resource, although it is difficult to exploit, at least at the present levelof technological knowledge. Usually this kind of energy is found at too great a depthand in rather scattered areas for an adequate exploitation on an industrial scale.Moreover, in its natural state it is manifested through emissions of hot water andsteam (fumaroles, geysers) with limited energy quantities or through volcaniceruptions, the latter being more dangerous than useful.Nevertheless, during the past few years, increasing attention has been given to theexploration and exploitation of geothermal resources and new extraction and25

26application technologies are eventually making feasible the use of geothermal basinswhich in the past had not been considered, both for their limited energy quantitiesand for the difficulties connected with their exploitation.The geothermal energy available has a low or very low temperature (between 30and 90°C), consequently it excludes a transformation into mechanical or electricenergy. Instead, it is useful for a direct use of heat, such as for urban heating plants,for greenhouses, exsiccation procedures, etc.In the near future, technological progress applied to the extraction and exploitationof this natural resource should make it more acceptable from the economic pointof view, considering also that it does not pollute and its environmental risk isminimum.The contribution of Geomorphology in geothermal research is mainly related tothe identification and location of open fractures or active faults, along which thecirculation and eventual outlet to the surface of steam and hot water is possible. Thisfield belongs to neotectonics, an area in which Geomorphology has many importantapplications, as will be shown in the following chapters.2.2 LandformsAs has already been stated, if landforms are valuable they can be called geomorphologicalassets and, therefore, may also be geomorphological resources in that theymay be or become useful to man, depending upon the economic, social or technologicalcircumstances existing at a given time (Fig. 12). Landforms are a part of ournatural assets which also belong to our cultural assets.In order to provide a framework for this topic, it should be specified that theconcept of culture is used here in its traditional meaning, which is derived from whatthe Romans called humanitas, that is, ''the whole body of knowledge and behaviour,which enables man to achieve his authentic human nature". Cultural assets may besubdivided into two categories: those that are more strictly ''natural" and those thatare more directly related to the "work of man". This is, however, a somewhatcontrived division, in that the two are closely linked, just as all cultural assets are andshould be seen as interacting. "Man-made'' cultural assets include documentary,artistic, architectural, historical and archaeological assets. Natural assets may besubdivided into biological and nonbiological assets.Knowledge of these assets is an indispensable priority if an awareness of theirworth and thus their correct collocation in Environmental Management is to beattained. In this way they may be protected and utilised without being destroyed ordegraded, and may be used in the most opportune ways.Indeed, landforms are among the most widespread and spectacular naturalnonbiological assets: a river gorge, a mountain peak, a natural bridge, a sea cliff andLANDFORMS GEOMORPHOLOGICAL • GEOMORPHOLOGICALif valuable ASSETS if used RESOURCESFig. 12. Relationship between landforms. geomorphological assets and resources.

the like. They have always aroused interest because of their scenic appeal. However,scenic aspects are not the only attributes that make such landscape elements important— at times, it is also their cultural significance that does so. Consider the scientificand educational aspects associated with the remains of Pleistocene glacialism forexample, the spectacular nature of a Dolomite landscape or of a Mediterranean coast,the value in tourism and economic terms associated with a beach in the Caribbeanor the cultural implications of a landscape in Greece.Landforms such as these ~ whose attributes of value lead to their definition ascultural assets — by analogy, can be called geomorphological assets, which in turnmay be considered and really become geomorphological resources if used by man(Fig. 12).The attributes that may confer value to a geomorphological asset are listed below:— scientific;— cultural;— socioeconomic;— scenic.By a process of generalization, these attributes may also be seen in other naturalassets. In the following paragraphs, they are described in more detail.From a scientific point of view and in the field of geomorphology, the importanceof a natural asset may be assessed according to four characters (Panizza & Piacente,1993):1) As a model of geomorphological evolution', e.g., a Karst doline, or an earth pillar.2) As an object used for educational purposes, e.g., a badlands area or a fluvialmeander.3) As a paleogeomorphological example such as a Pleistocene loop moraine or ariver terrace.4) A landform can be considered a geomorphological asset because of its scientificaspects also when it is an ecological support, maybe because it is the exclusivehabitat of a particular animal or plant species, which are indispensable elementsin an ecosystem: some wetlands or debris accumulations may provide examples.However, in this case, other disciplines, such as Botany or Zoology, rather thanGeomorphology, will indicate the scientific attribute of the geomorphologicalasset. In other cases, the determination of the scientific value of a particularmorphological feature, such as a cave or a ledge that were once the site of anancient human settlement, may lie within the bounds of Archaeology.Each of these characters can assume a higher or lower value owing to its rareness,i.e., its interest in spatial terms; therefore a different level of interest can be ascribedto each of the four categories of the above defined characteristics:— local;— regional;— super-regional;— world-wide.From the cultural viewpoint, a geomorphological asset may belong to the world ofart or to a cultural tradition, as, for example, the landscapes depicted by Venetian27

28painters in the sixteenth century or Mt. Olympus, the abode of the pagan gods.A geomorphological asset may also acquire socioeconomic value if it can beutilised for the purpose of tourism or sports, as for example an Alpine valley, a trailfor Nature walks and excursions or a rock wall equipped for mountain climbing.The scenic element may also be a geomorphological asset both in an intrinsicspectacular sense and because of its appeal as an attraction, which can make it easierfor people to approach environmental issues and increase their knowledge andawareness.From the above observations, one may deduce that a geomorphological asset maybe either a landform or raw material, or even both. For example, a debris cone canbe considered as a geomorphological asset, as a landform, if certain scientificcharacters (e.g., as a model of evolution or a feature of paleogeomorphologicalevidence) or if socioeconomic characters (e.g., as an area equipped for Natureexcursions) are contained within it. It may instead be considered geomorphologicalasset as raw material if the debris it is made up of can be used as aggregate to bequarried.Legislative initiatives to safeguard and utilize natural resources in general, andgeomorphological assets in particular, imply, in certain cases, an appraisal of theirvalue in quantitative terms. This is especially the case in ''Environmental ImpactAssessment''. Such problems are being posed with increasing urgency, owing to therapid increase in the number of projects for urbanization, civil works, etc., in manyareas. Growing human intervention on the earth's surface is progressively increasingenvironmental deterioration and the social demand for recreation areas, uncontaminatedlocalities, parks and protected areas. Nevertheless, the appraisal of theabove mentioned "value" and impact is a difficult problem to solve, linked as it is tothe difficulties involved in providing an objective and quantifiable evaluation of thevarious geomorphological aspects of the landscape.The studies that must be conducted involve the concept of measure, that is, thenecessity of assigning to each "environmental marker" (and therefore, also togeomorphological assets) a "weight", which in turn, permits an assessment inquantitative terms of their "environmental value" and a comparison with othermarkers, to permit the definition of a hierarchy of priorities. The criteria that can beused for the assignment of this "weight", that is, for a "measurement" of landscapefeatures, may be one or more of the four types previously illustrated.The scenic/aesthetic criterion is to a great extent, of an intuitive nature. In thiscase, the approach to Nature depends upon the individual contemplating it and his/herstate of mind at the time. It is derived from feelings which being personal perceptionsare highly subjective, it is therefore difficult to value and compare with the feelingsand perceptions of others.Several procedures for such evaluations exist in literature (i.e., Linton, 1968;Fines, 1968; Leopold, 1969). Some of these present morphometric methods ofmeasuring several landscape components that have been judged as representative ofthe scenic quality of the landscape. Other procedures appear to be more subjectiveand they concern the perception of the landscape as a whole in qualitative terms.

Numerical rating scales are proposed. The limitations appear to be considerable in allcases, due to the subjectivity inherent in judgements conditioned by both thesensitivity and the experience of the observer, either because several importantcomponents are omitted and a vision of the landscape as a whole is lost, or becauseby breaking up the resource itself it is distorted and permanently stripped of itswholeness and essence.The merits of the cultural and socioeconomic criteria will not be discussed herebecause they concern disciplines other than geomorphology.The geomorphological approach, however, is based precisely on scientificknowledge of the natural resource, the perception of the laws regulating its evolutionand an awareness of its significance for humanity. Therefore, this is a task that canonly be performed by well-trained geomorphologists who can accurately identify andevaluate those attributes.On the other hand it is of fundamental importance to try to approach the asset inits entirety without preestablished tables and matrices because there are otherintersecting or combining variables that will inevitably come into play and augmentor detract from its value. We are referring here to human forces and particularly tosocioeconomic, cultural and political interest groups, which may select a given assetas the most significant as a tourist attraction, for example, or as the best scientificexpression of certain environmental processes, and so on.A landform becomes a geomorphological resource only if it has socialimplications, that is, only if other parameters, external parameters, come into play toinvest it with value (Panizza & Piacente, 1993) (Fig. 13).As long as a particular river, or a particular landscape is studied by and knownonly to scientists and researchers, it remains ''private" knowledge and its potential asa resource does not materialise. However, if the scientist and the researcher publiciseit, thus making its cultural and environmental significance known to the generalpublic and thereby give it a social dimension, then the landform becomes ageomorphological resource in the eyes of society at large.One assessment, however, should certainly be carried out and that is the evaluationof the asset's continued existence over time. More specifically, this involves the29EconomicsLANDFORM 1 ORGA^STIONCulture< PoliticsTourismGEOMORPHOLOGICALRESOURCEFig. 13. Relationship between landforms and society.

30correct regulation of its utilization when conflicting interests develop. Such conflictsinclude scientific research versus its fruition, the restriction of access to the landformversus the demand for knowledge and educational purposes, direct use versus pureobservation, etc. A preference for one alternative over the other in a sort of a prioridiscrimination is not possible. On the other hand, choices must be dependent uponguarantees for the asset's continuing existence. This can be achieved by defining theasset's "capacity load" in relation to various functions. In other words, when andwhere a geomorphological resource has a social implication (see human activity: e.g.,tourism) an environmental impact is likely to occur (see Fig. 1).Thus, the hierarchy of evaluations may be summed up as follows: in the firstplace there is the existence of the landform; the evaluation as a geomorphologicalasset comes second, while its usage comes third. However, care must also be takento create equal opportunities for use by all parts of society as the resource has alsoa collective, community value which is different from the value it has for theindividual.These problems take on considerable complexity when considered also in the lightof the present decline of two cultural concepts that originated in the first half of theseventeenth century with the Galilean and Cartesian dichotomy.The ascent of reason, on the one hand, had created the basis for the developmentof science and technology and led to the scientific empiricism of the Enlightenment,as well as to the methods of simplification and subdivisions of Positivism. On theother hand, the limits of science, conditioned by its subjection to free will, had ledto conceptions based on abstraction and ideology.Environmental impact studies have appeared at a time in which the ideologicalevolution of postindustrial society is bringing about an increase in critical andnegative attitudes towards technology and its effects on Nature and the environment(e.g., opposition to nuclear energy, genetic engineering, polluting industries, etc.). Atthe same time, however, the pragmatic application of these ideological trends to dayto-daysocial and political administration is a difficult operation without the supportof science.One of the needs of this postindustrial age is perhaps a return to "neohumanism",a holistic concept of culture. Environmental assessment studies provide the means tocombine scientific, economic, social and cultural aspects in a harmonious andintegrated concept of the landscape, in order to achieve a balanced relationshipbetween humanity and the environment. This kind of holistic approach to the environmentshould provide a comprehensive view of environmental problems, including thebasic elements needed by policy- and decision-makers for correct choices.2.3 A method for surveying, mapping and assessing landforms asgeomorphological assets**by Mauro MARCHETTIThe conceptual principles and scientific method here described were employed in an

interuniversity study and can be taken as an example for a research on evaluation oflandforms as geomorphological assets (Carton et al., 1994, modified).In the first phase of the work a ''Map of geomorphological units" is compiled. Adocument of this type may be easily derived from a detailed geomorphological map,where the geomorphological units are grouped according to their morphogeneticnature (e.g., glacial, river, karst). These groups comprehend more detailed elementsof the rehef (e.g., a glacial cirque, a river meander, a slope subject to a network oflapies, etc.). Other details may also be taken into consideration, depending on thescale and aims of the research.During the second phase the scientific characters of landforms, leading to theevaluation of each unit or part of it (depending on the detail required) as ageomorphological asset, are indicated (e.g., as a paleogeomorphological example, seeTable 2). In some cases other disciplines may include other assets, such as wetlandsor the caves mentioned in the previous chapter.The third phase is concerned with the assignment of a differentiated level ofinterest to each unit or element considered as a geomorphological asset, according toits degree of scientific importance in terms of space, that is, whether its importanceis of a local or more general nature (Table 2). For example, a glacial landform on anAfrican mountain may be of value on a superregional or even a world-wide levelbecause of its rarity, even if it is poorly preserved, whilst the same type of landformin the Alps may not be of any particular geomorphological significance other thanpurely local, even when properly preserved, because it is part of a widespread andcommon morphology in that mountain range.The product of these operations is a Map of geomorphological assets. Itspreparation can be carried out through two techniques: manual and automatic. Thefinal data, although containing the same quality and quantity of information, differon account of the type of graphic representation.For the representation of geomorphological assets, the ''manual" technique makesuse of the same symbols as those applied in geomorphological maps: the value ofeach asset and its level of interest are deduced from a table/legend accompanying themap itself. From the map it is possible to recognise the level of interest and the31TABLE 2Scientific characters and spatial levels of interest of geomorphological assetstype of attributecharactermodel of geomorphological evolutionlevel of interest^ /'"^ /scientificobject used for educational purposespaleogeomorphological exampleecological support' y ^^

32character of each landform that in itself or with others makes up a geomorphologicalasset.The "automatic" technique represents geomorphological assets by defining theassets' areal extension. Their character and level of interest are identified by meansof a legend based on a scale of different colours or shades.In the first case (manual technique) the identification of the geomorphologicalasset is performed directly by the geomorphological map's surveyor who, thanks tohis/her knowledge of the territory, will select those landforms to which one or morescientific characters could be attributed. Only the landforms selected will berepresented on the map of geomorphological assets, with their specific geomorphologicalsymbol (i.e., scarp, ridge, slide) and colour corresponding to their morphogenetictype (i.e., fluvial, glacial).Each geomorphological asset is progressively numbered and inserted in a matrix(Table 3), according to their characters and level of interest.Thanks to the use of the geomorphological symbology, this map gives aparticularly plastic and direct representation of geomorphological assets. It is thereforemore easily understood and particularly useful and suitable for general use (parks.Nature reserves, etc.).During the subsequent phases quantitative values will be assigned to eachgeomorphological asset, in order to give these components of the landscape theirproper weight (see 6.4). This will permit not only a ranking of the assets, but alsotheir comparison with other environmental components.In the second case, the ''map of geomorphological assets" can be prepared usingautomatic techniques (Carton et al., 1994; Cavallin et al., 1995). The use ofcomputers and in particular of GIS supports is in fact necessary for processingmegabytes of geomorphological data. Also in this case the basic map is thegeomorphological map. This map must be subdivided into polygons which representareas characterised by a morphogenetic type (i.e., fluvial, glacial, etc.). Also thegeomorphological feature (i.e., scarp, ridge, slide, etc.) or the characteristics of thedeposits are represented on it.TABLE 3Matrix for landforms selected as geomorphological assets. The numbers (1 — 15) refer to each landformand to an explanatory listLevel of interestCharacterModel ofgeomorphologicalevolutionObjects usedfor educationalpurposesPaleomorphologicalexampleEcologicalsupportWorldwideSuperregionalRegionalLocalNonsignificant397, 13, 14111556, 1012, 4812

Each polygon is automatically associated to a progressive number inserted as asimple record in a geographical database system (Table 4). In it the first record is thenumber of the polygon (i.e., 80), then the morphogenetic type (i.e., periglacial = 3)and the landform (i.e., landslide degradational scarp = 7), then for each type of thefour characters (i.e., paleogeomorphological example = c) (see Table 2) a numbercorresponding to the level of interest (1 = world-wide; 2 = super-regional; 3 =regional; 4 = local; and 5 = nonsignificant) is assigned. If a polygon does not showany kind of geomorphological interest, nothing will appear in the relative columnsand in the next column (z = polygon not interesting as a geomorphological asset) azero (0) will be inserted.Since one or more polygons can be grouped in a geomorphological asset in thenext column, the progressive number (N) of the geomorphological asset to which thepolygon belongs is expressed, and in the following columns the character and levelof interest are expressed not only for the single polygon, as in the previous columns.TABLE 4Geographical database for a digital map of geomorphological assets33Polyg onAssetnMFCharacterNCharacterabcdzabcd808182838485868788899091929394959697989910010110210334434434343333333434344371097159787975757579797801543444444434944000000000000000007791011111243444444434944Legend: n) progressive number of the polygons; M) morphogenetic typology; F) landform; a,b,c,d)characters of landforms; z) landform negligible as asset; N) progressive number of assets.

34but for the whole geomoq^hological asset. If the latter is composed by only onepolygon, the character and level of interest of the geomorphological asset are identicalto those of the single polygon. On the contrary, if a geomorphological assetcorresponds to more than one polygon, the relative column will show the sameprogressive number for the polygons that make up the asset, and in the next columnsthe characters and levels of interest of the geomorphological asset are the same foreach polygon belonging to the asset. For each quality the level of interest ismaximum and derives from the comparison of each polygon making up the asset. Tothis purpose, many kinds of software installed on suitable hardware can be used.In order to prepare a schematic digital asset map, a Central Processing Unit(CPU) is necessary, which is the heart of the system, connected to a graphic tabletwhich permits the digitalisation of geographical data in vectorial format. A scannermay be useful for a quick acquisition of geographical data. Also devices for therepresentation of the results are necessary, such as videos, plotters and printers.The product of digitalisation is a set of lines defining homogeneous areas(polygons). This further step is simply acquired by means of CAD-type software. Thenext step is given by the transformation of the vectorial data in raster data. In thisway the map is divided into pixels whose dimensions are determined by the degreeof final precision and by the density of the entry data. The passage from vectorialformat to raster format is important and necessary since in this way an attribute canbe given to each pixel of the map. Then each pixel of the map is linked to a large0---rJ\ \ ^\'-' C \Fig. 14. Selection map of geomorphological assets in the Castelnuovo del Zappa — Annico area west ofCremona. Legend: 1) regional level of interest; 2) local level of interest (after Marchetti et al., 1994).

number of codes, corresponding in the case of the geomorphological assets to thecodes previously described which, finally, are stored in a database system linked tothe geographical data. In this manner each pixel holds all the attributes relative tomorphogenetic typology, form, character and level of interest of the polygon, numberof the relevant geographical asset, character and level of interest of the geomorphologicalasset.Therefore, the structure of the database allows the map representation to becarried out as a function of each single attribute.An example of "map of geomorphological assets" elaborated using automatictechniques is shown in Fig. 14 (Marchetti et al., 1994). By comparing it with themanual one, the character and level of interest of the asset are immediatelyemphasized but not the type of landform. Nevertheless, this system has the advantageof being constantly updated, and also provides precise information according todifferent requirements. It is therefore a useful tool for urban and territorial planning.353 GEOMORPHOLOGICAL HAZARD3.1 Geomorphological instabilityIn chapter 1 the concept of geomorphological hazard was introduced, with referenceto geomorphological instability phenomena. It is therefore opportune to define themeaning of the term unstable landform: it is either ''a form which is not inequilibrium with the natural environment and which tends to reach a balance bymodifying itself or "a form which has already reached equilibrium althoughremaining a particularly dynamic one". They are all landforms evolving in a waywhich disturbs human activities: for example, a landslide or a meander cause moreor less marked environmental modifications due to erosion and accumulationprocesses.Moreover, instability must be considered in relation to the phenomena that causeit; one cannot speak about instability in absolute terms since an area could prove tobe unstable with respect to a certain process (e.g., slope movements) and, on thecontrary, stable with respect to others (washing out, fluvial erosion). The indicationof the type of instability can also offer the essential elements for the choice of themost opportune and effective remedies. Finally, there are more or less acceptabledegrees of instability according to the various social uses: the type and degree ofstability required for a nuclear plant is quite different from that considered sufficientfor the construction of a road.The following paragraphs illustrate the main kinds of geomorphological hazardin the widest sense, where Geomorphology can give a research contribution withsome examples of specific investigations. The last paragraph introduces a mappingmethodology for geomorphological hazard representation.

363.2 Soil erosion**by Giuliano RODOLFI and Dino TORRI3.2.1 IntroductionSoil can be considered as a natural consequence of a situation of dynamicequilibrium established in time in the midst of the following environmentalcomponents: climate, bedrock, relief morphology, flora and fauna, antropic activity.It can be ranked between the main natural resources because its peculiar position atthe intersection among atmosphere, lithosphere and biosphere makes it one of theprincipal actors in myriads of interactions. Obviously, any given soil type can bemodified in its potential capacities and characteristics by altering the dynamic equilibriumunder which that soil was formed. Often a more or less sharp but progressivedecline of soil production capacities accompanies quick and intense modifications.Therefore soil should be considered as a natural resource subject to deterioration,which may be renewed only with difficulty in the long term. This chapter willexamine one of the main groups of processes trough which soil capacities aredepleted: soil erosion.3.2.1.1 Definitions and terminologyTwo main groups of processes may be distinguished:1) Soil forming (i.e., pedogenetic) processes, that lead to a progressive increase ofsoil thickness at the expense of bedrock and to its vertical differentiation intohorizons {soil profile).2) Morphogenetic processes, that are dominated by factors external to the soil(mainly climate). Within the more general framework of a relief-demolishingphysico-mechanical action, they determine soil disgregation with removal of soilmaterial and consequent thinning of the profile.Two main situations, due to interactions between pedogenesis and morphogenesis, canbe identified:— A biostasis regime, which is a state of biological equilibrium between soil,vegetation and climate. Here, pedogenesis prevails on morphogenesis, as in the intertropicalbelt with rain forests or at middle latitudes in flat morphology. Pedogenesismay produce very deep soils with profiles well differentiated into horizons.— A rhexistasis regime, when the biostasis regime is broken. This may happen inparticular climatic situations, or following exceptional natural events that could alterthe morphological situation of certain areas of the Earth's surface. Direct antropicactivities also cause intense perturbations. All these cause morphogenesis to prevailon pedogenesis. Then the soil undergoes progressive thinning up to the point of beingcompletely removed, with outcropping of the inert bedrock. This often leads toprogressive desertification in arid and semiarid regions. Desertification, as well as inother cases of severe erosion, is often caused or accelerated by human activities:precipitation is rare and often determines intense and aggressive soil erosion,

preventing effective pedogenesis; the lack of vegetation, although discontinuous,favours aeolian erosion which becomes the fundamental morphogenetic agent.Morphogenesis and pedogenesis can also compensate each other. As the soil isdeveloped in depth, erosion removes its superficial horizons at the same rate. Soilthickness remains constant and so does its characteristic profile; the only effect of thisprocess is a slow but progressive relief levelling (geological erosion).In the last two situations, the prevailing morphogenetic process is called soilerosion or surface erosion or, more generally, erosion.A distinction can be made (Zachar, 1982) between natural erosion, essentially dueto natural factors, and anthropogenic erosion, connected more or less directly withhuman activities. In each case the intensity of the process and its possible consequences(erosion hazard) are of different significance.In normal natural conditions without any noticeable interference due to anthropicactivity, erosion is kept within acceptable limits (normal erosion) and the soilproductivity remains constant. As for antropic activities -^ in particular farming ifcarried out with conservation techniques — a slow down of the erosional process(inhibited erosion) could take place achieving situations of low or nil hazard.An exceptional natural event (intense and concentrated rainfall, mass movement,seismic shock, prolonged drought) can rapidly alter the equilibrium conditionspreviously discussed and trigger soil abnormal erosion.Similar consequences are attained when disequilibrium conditions are directly orindirectly determined by human activities (deforestation, nonconservative farmingsystems, earth movements, etc.); in this case the degradation process rapidly increasesand the term accelerated erosion is used. When abnormal erosion interacts withanthropic activities it is usually amplified.The interaction scheme is shown in Fig. 15.37Fig. 15. Relationships between soil erosion types and related hazard levels.

38Any component of the natural environment (such as air or water in its differentphysical states) becomes an erosion factor when, assisted by gravity, it is capable ofmodelling in the soil (and/or bedrock) a particular form (erosional landform), usuallycharacterised by a transversal or longitudinal upward concave profile. The samecomponent can act as a vector, transporting the eroded material towards places withlower energy. Here it can build a corresponding accumulation or depositionallandform which tends to fill pre-existing concavities or to assume and maintain aconvex profile.These forms of the earth relief are mainly differentiated according to the natureof the modelling factor (Table 5) and since there are several factors, a noticeablevariety is eventually produced. Therefore the use of a geomorphological criterionseems appropriate to illustrate the various aspects of the erosive process and attempta classification of the derived forms.3.2.2 Physical bases of erosion3.2.2.1 Forces produced by fluids in motionSoil erosion is the result of detachment, transport and deposition processes. Thedeveloping of these processes, their relative importance and intensity are stronglyinfluenced by the particular set of initial conditions that characterise the soilvegetation-managementcomplex. Let us survey how processes act and interact andhow they are linked to soil, vegetation and management characteristics, beginningwith the forces generated by fluids in motion.The movement of a fluid may either be well organized, describable as the motionof parallel sheets gliding one over the other (laminar regime) or turbulent withdevelopment of whirls and eddies. The degree of turbulence of a fluid motion ismeasured by means of an adimensional ratio called Reynolds' number:R^-aiL (1)VTABLE 5Types of erosion in relation to the determining factorsDominant factorErosion typeWater Water erosion (*)SnowNival erosionIceGlacial erosionWind Wind (aeolian) erosion (*)GravityMass erosion, mass movementsOrganismsOrganic erosionManAnthropogenic erosion*Asterisks mark the types generally referred to with the general term "soil erosion"

where w, h and n are, respectively, the mean velocity, the height and the kinematicviscosity of the fluid in motion.If Rf: is less than 200/300 the flow is laminar and flow velocity profile isparabolic. When R^r is over 1,000 the flow turns completely turbulent and the velocityprofile is logarithmic. In the latter case, velocity at a given depth is a temporal meanmade in order to eliminate the main effect of turbulence, i.e., the continuous variationof local velocity values. In other terms, one could say that the velocity in a givenpoint (x,y,z) within the fluid (moving along the x-axis) is characterised, at a giveninstant t, by a velocity u(x,y,xj) resulting from the vectorial sum of the followingcomponents:39w(x,y,z,0 = w(x,y,z) - i7 (jc,v,z,r) - ii^{x,}\zJ) ' uix^\z.t) (2)where the components u- (/ = xs,z) have a nil temporal mean. Velocity i7(x,y,z,t) isthe temporal mean value at point {x^\z) and time /. If the Oxy plane coincides withthe soil surface, then u(x,y,z) (from now onward abbreviated as u(z)) is the temporalmean velocity of the fluid at height z from the soil surface. The relationship betweenu(z) and z is as follows:uiz) = —u^Logi^^) (3)kkswhere k is von Karman's universal constant {k = 0.4 for clear fluids), k^ is a measureof the bed roughness, u^ is the flow shear velocity in the neighbourhood of the bed.Equation 3 is valid for 30.2z » k^, otherwise the flow has laminar characteristics andthe velocity distribution is of the following type:u(z) - l^}I}^z(2h - z) (4)2vwhere g is gravitational acceleration, a the local slope angle and /i^, coincides withthe fluid thickness when the latter is completely in the laminar state, otherwise it isa convenient value used for linking curves (4) and (3). The situation is depicted inFig. 16.The fluid motion generates forces which act on the soil grain both for detachingand transporting it. Such forces can be ascribed both to the laminar and to theturbulent flow. The former are estimated by means of relations such as the followingone, valid for spherical grains with diameter D:F = 3K^uD(\-^R}!ll.) (5)16v

40a«T3T3"5turbulent layertransition zonelaminar layerfluid velocityFig. 16. Flow velocity profile for turbulent regime.where r| is the fluid dynamic viscosity and ii is the fluid velocity in the neighbourhoodof the grain (u being the intensity of the velocity vector). If the second term inbrackets is negligible, then Eqn. 5 becomes Stokes' equation, normally used inlaboratory tests to determine the particle size distribution of fine sediments.When the motion of the fluid is turbulent, the term proportional to the 2nd powerof velocity (Eqn. 5) becomes dominant. In general terms, the force expressed by thefluid becomes:C^A p\u\ (6)where C^ is the drag coefficient (Q is about 1.1 to 1.2 for a disk placed across theflow, 0.2 to 0.4 for a sphere, 0.004 for an ellipsoidal body very elongated in the flowdirection); p is the fluid density and A is the surface of the grain cross-section. Thefact that the forces in Eqns. 5 and 6 have the same direction as the velocity meansthat, in the case of laminar flow, the force can be considered as parallel to the groundsurface whilst in turbulent flow the force always shows a component normal to theground surface. When this component has a direction oriented upwards, lifting forcesoriginate; they are extremely effective in causing the detachment of the soil grainsand afterwards in keeping them in motion.In the case of water erosion, the flow shows transitional characteristics betweenlaminar and turbulent. It is usually turbulent in the case of channeled flows (such asrill and gully flow), while it may be laminar in interrill, diffused overland flow. Inthe case of wind erosion, the flow is always turbulent.As previously stated, the local velocity variations of a fluid in motion are alwaysremarkable and therefore also the force of Eqn. 6 will undergo violent fluctuations.When the fluid is water, an example of the variations can be given by Naden's (1987)results. For turbulence lasting 0.2 s Naden suggests that ujzj) be normally distributed

with zero average and standard deviation given by the following empiricalrelationship:41a^iz) = 0A6u(z)(-f'' (7)zSimilarly, the ujzj) component, which is always characterised by a zero average, hasthe following lower standard deviation:aXz.t) = 0.17a/z,0 (8)3.2.2.2 Forces resisting detachmentSoil primary particles are usually linked by interparticle forces of varying nature andintensity. The spatial variation of the bonding forces causes the creation of aggregatesof primary particles, that are linked to each other by intra-aggregate forces moreintense than those linking the aggregate to other surrounding aggregates.The direction of application and the intensity of the detaching and bonding forcesdetermine the prevailing dimension of the removed aggregates. The spatial dispersionof the two types of forces — detachment and bonding — contributes to the sizedistribution of the eroded aggregates. Obviously this means that together withaggregates single primary particles will be eroded also, hence the use of the genericalterm "grains" throughout the text. This definition of aggregate implies the identificationof the forces resisting erosion with low-intensity bonding forces whichcontrol grains of such dimensions that the efficiency of the entrainment process ismaximized.Together with intense and time-stable bonds there are others, probably due toorganic matter, which show seasonal and longer term dynamics (Nestroy, 1993;Rousseva, 1989), depending on microbiotic activities and therefore on the type ofvegetation present, farming techniques, local climate (which include slope aspect withrespect to sun and wind; see Imeson & Lavee, 1996; Torri, 1996). Still others are dueto clay particles and are therefore conditioned by the presence of water and solute.In some cases, generally characterised by the presence of sodium in the exchangecomplex and low electrolyte concentration, bonding forces can even be transformedinto deflocculant repulsive forcesAlso frost and thaw processes can modify the state of surface aggregates: anexperience common to whoever walks in the countryside on ploughed fields after anovernight frost is to find little heaps of isodiametral aggregates (often around 1 to 3mm in diameter). On the contrary, during warm and dry periods the ground surfaceis richer in microaggregates, which are often powdery.Naturally, any action favouring a greater or lesser packing density of the grainsinfluences the bonding forces, their spatial distribution and the dimensions of theeroded grains. Among these actions, ploughing, grazing and the traffic of heavy

42machinery have direct consequences on the distribution and intensity of the bondingforces.With regard to erosion, these resisting forces, concerning the grains exposed onthe ground surface, can be considered as Coulomb-type forces, that is withcomponents due respectively to internal friction and cohesion. Such a resistive forcehas a direction coincident and opposite to that of a detachment force. In the case thatthe detachment is mainly due to lift, the resisting frictional term may disappear andbe substituted by the submerged weight of the grain.3.2.3 Water erosion3.2.3.1 IntroductionWater erosion is responsible for the most outstanding and most widely representedlandforms. Water is in fact the main modelling agent of the Earth's surface at present:it entrains, transports and deposits large volumes of material in a very short time. Itsaction can affect both the innermost continental environment and, to a much lesserextent, the thin belt of transition to the marine environment (Table 6).Indeed, the dynamic action of the sea (waves, tides, streams) dominates coastmodelling: with high and rocky coasts, submerged shelves and cliffs are formedowing to abrasion, whilst low and sandy coasts can be affected by coastal erosion.In the continental environment water erosion produces effects which areproportionally related to the intensity of the process and the nature of the soils andbedrocks. In general terms it can be said that the intensity of erosion is strictly linkedto the volume of rain that reaches the soil in a certain time unit (e.g., annual meanrainfall). One should nevertheless consider that with the increase of annual rainfallin natural conditions, the density of the vegetation cover also increases. The increasein vegetation cover acts as a limiting factor to erosion because it reduces rain-dropimpact forces, favours infiltration, and limits overland flow volume and velocity.Therefore, the lowest values of water erosion are attained either in arid regions,owing to the scarcity of precipitation (desert or subdesert areas) or in regions withintense rainfall but characterised by a thick vegetation cover (rain forests). In generalTABLE 6The various types of water erosion subdivided according to the active agent and the environment affected(after Zachar, 1982, modified)Environment Erosion factor Erosion typeCoastal Waves, tides, marine streams Abrasion, littoralContinental (slopes) Rainfall SplashOverland flow (runoff)Interrill, rill, gullySubsurface waters (internal flow) Eluviation, leaching, piping,mass movementsSurface and subsurface waters Polymorphic (badlands)Continental (thalwegs) Streams (torrents, rivers) Vertical, lateral (undermining)

terms, the erosion maxima are recorded in correspondence with mean rainfall valuesranging between 700 and 1,000 mm/year, because of the competition between rainfallerosivity and vegetation protective effect. This is, for example, the situation takingplace in circum-Mediterranean regions where erosion forms reach their maximumexpression. This is due to the simultaneous effects of relatively high rainfall and avery discontinuous vegetation cover, with vast surfaces that have long been subjectedto farming activities.The erosional process may assume various aspects that can remain isolated butcan also be connected both in time and space and from higher altitudes to lower ones;each of these aspects produces its own landforms, which are often clearly identifiableand distinguishable from all others.In the next chapters the complexity of the erosional processes will be illustratedand the main relief forms derived from these processes will be defined, discussingin particular water erosion and, more generally, wind (aeolian) erosion. Finally,some characteristics of the most current models of erosion assessment will bedescribed.3.2.3.2 Impact of raindropsLet us now try to follow what happens when it rains. The soil is initially characterisedby a distribution of resisting and bonding forces that is altered during thewetting process, especially when the soil is initially dry. Usually some clay dispersionoccurs, which may sometimes be sufficiently intense as to dominate detachment Inany case, clay dispersion, when present, influences the whole erosion mechanics(Shainberg et al., 1992). In particular it is an important cofactor in the formation ofsome kinds of gully that can evolve into proper badlands (Oostwood & Bryan, 1994).Still during the first stages of a rainstorm, when soil has an initial low moisturecontent, a rapid wetting can cause slaking of the aggregates with detachment ofmicroaggregates and particles (Yoder, 1938, quoted in Bryan, 1969; Le Bissonnais,1990). The process takes place when the water occludes the external orifices of thepores of an aggregate.Thus the air within must get out by passing through the wateritself. If the penetration velocity of the water inside the aggregate is larger than tothat of the air diffusion through the water, then air is compelled within lower andlower volumes and, as a consequence, there is a pressure build-up which eventuallybreaks the aggregates. If the material expands while water penetrates then otherbreaking forces develop due to differential volume expansion at the water penetrationfront (producing fissures transversal to water penetration direction).The processes so far described do not require any mechanical energy butsimply water: they can be reproduced by utilising a foggy-like rain or by submerginga dry soil sample into water. On the contrary, during rainfalls a noticeablequantity of mechanical energy is transferred to the soil by the impact of the raindrops.The impulse generated during the impact is used to break the drop, deform asmall volume of soil, detach particles and aggregates and eject them together withwater droplets all around the impact areola. In particular, during the collision a nearly43

44circular crown of jets is formed, moving away at high velocity from the impact point.Thus very intense forces are produced. They detach and drag away particles andmicroaggregates (seldom exceeding 2 mm in diameter), each of them wrapped withina droplet. They are then ejected and, after having covered a nearly parabolictrajectory, fall to the ground.The summarised description given in the previous paragraph is derived from thework of several researchers among which worthy of quotation are Engels (1955),Harlow & Shannon (1967), Ghadiri & Payne (1988) and Mc Carthy (1980).The material ejected by an impact is redeposited around the microcrater,according to a law generally well approximated by an exponential (Poesen & Savat,1981; Reizebos & Epema, 1985, Torri et al., 1987b).Let us now examine how the drop impact interacts with the soil surfacemorphology. Several studies (Ekern & Muckenhirn, 1947; De Ploey & Savat, 1968;Savat, 1981) showed that with respect to the drop impact point, more material isdetached downslope rather then upslope and total detachment increases as soil surfaceslope angle increases. The first physical explanation of the phenomenon was givenby Torri & Poesen (1992) and is based on the considerations hereafter illustrated. Letus consider a drop falling vertically. In this case (Fig. 17,a) the mass upslope of thevertical line, which passes where the drop first touches the soil, is compelled to move(in the form of lateral jets) with an upslope component of motion, whilst the mass onthe left of the line will have a downslope component. If the force applied to thedetachment of soil particles is proportional to the water mass passing over them, thenthe quantity of material removed downslope is necessarily greater than that removedupslope. In fact, the vertical line subdividing the two drop fractions passes by thedrop centre, dividing it in two equal parts, only when the slope is nil. In all othercases the line is always located upslope.Moreover, as slope increases, also the total mass of detached soil increases. Thisis due to the fact that the component of the gravitational force (G in Fig. 17,b),parallel to the ground surface and acting on aggregates and particles, behaves as adetaching force when the direction of the erosive force is downslope. When F^ isdirected upslope, then G acts as a resistance. Since a greater soil mass is ejecteddownslope, the gravitational force is mainly acting as a detaching agent. This factcorresponds to a net increase of the total detachment force, and therefore of the totalmass removed, with increasing slope. The overall effect on detachment is describedby an integral equation resolvable with numerical methods (Torri & Poesen, 1992).The overall result on detachment is shown in Fig. 17,c.This effect is important only on steep slopes such as those, for example, that canbe measured on the surfaces of clods. In fact the gradient felt by the drop duringimpact is not that of the hillslope or of the field, but that of the impact areola (Torri& Poesen, 1992).The fact that the ground surface is locally inclined implies that the mean jumpdistance of the ejected material is itself asymmetrical. The downslope length isgreater than the upslope one and this difference is even more evident with theincrease of the slope. The global effect of a more intense downslope detachment and

45impinging dropupstope splashingdrop massdownslope splashing. -^ drop mass(a)FdRdRelative Splash1 Detachment2 ](c) 0 10 slope {%) 30Fig. 17. The effects of a vertically falling raindrop are schematically shown: a) the upslope splashingfraction of the impinging drop is smaller than the downslope part: b) the diagrams of forces depicting bothupslope and downslope particle entrainment show that gravity may either help (downslope) or resist(upslope) detachment; c) the overall effect of slope on detachment is shown for three soils with differingangle of friction (25, 35 and 55°).a longer jump length is a net downslope sediment flow. The flow direction, however,can be strongly modified by the wind (Poesen, 1986) which can even invert it.The effectiveness of the drop impact can be noticeably diminished by thepresence of water on the soil surface. In fact, when crossing water, a drop reduces itsvelocity before reaching the soil. Hence the crown of lateral jets formed duringimpact will act over a smaller soil surface while their force will be partly used forremoving the underlying water layer. Finally, the material is ejected with a morevertical trajectory. In other terms, with the increase of the thickness of watercovering the soil there is a decrease of material detached and of the mean jumpdistance (Palmer, 1963; Torri et al., 1987b; Profitt et aL, 1991). In particular.

46according to Torri et al. (1987b), the detachment decreases exponentially with waterdepth.Let us now consider how the above described processes interact. It is obvious thatthere is a net flow of material ejected downslope since both the mean distance runby the particles and the quantity of particles ejected downslope is greater. Thedownslope net flow increases as slope increases. The process is further intensified bythe presence of water (in puddles among the clods or in interrill and rill flow). In factthe detachment in the hollows among the clods is greatly reduced by the protectiveeffect of water, thus the flow towards the top of the clod is reduced. In other terms,marked sedimentation takes place among the clods, while erosion is observed at thetop of the clods themselves. It can therefore be said that one of the main effects ofthe drop impact consists in the levelling of surface roughness. At the same time, thequantity of mobilised material is very high. Generally this is the main source ofsediments that in part will be afterwards removed by surface runoff.The combined action of the mechanisms so far described contributes to theformation of a thin surface layer of soil with reduced porosity, therefore with lowhydraulic conductivity. Where erosion is prevalent, such as on top of the clods or onsmall reliefs, this process -^ known as sealing is due to soil compaction caused bydrop impacts (structural seal). On the contrary, where redeposition is dominant theformation of depositional seals takes place. The two types of seal differ alsomorphologically since the second type is characterised by relevant thickness and aparticle organisation that partly depends on the local sedimentation environment. Thefirst, on the contrary, depends basically on the depth (a few millimeters) to which theeffect of drop impact is felt. Owing to erosion, a portion of the compacted materialis eroded during subsequent drop impacts. This causes a maximum of possiblereduction of porosity beyond which the effect of removal and remixing of the soilgrains is no longer felt.3.2.3.3 Overland flow erosionFlow detachmentDetaching forces in concentrated as well as in diffuse overland flow are thosepreviously discussed (Eqn. 1—8). Local flow velocity fluctuations (turbulences) causethe detaching forces to fluctuate, giving rise to a temporal distribution of forces inany given spot.Naden's Eqns. 8 and 9 show a temporal distribution of overland flow forcesacting per unit of soil surface in a given position. In that particular position soilgrains are found which are bonded to the soil by means of any strength belonging toa certain distribution of resisting forces (g(R)), generally more intense than detachingforces. If resistance falls within the intersection area between the distribution curvesof the detachment forces and the resisting ones, then detachment takes place. Let usnow suppose that the two distributions are representative of the general situation ofa given surface: the probability that the detachment event takes place is given by theprobability that during the observation time interval /,, the detachment force is greaterthan resistance. This can be written as follows:

47Fig. 18. Erosional-depositional patterns resulting from "up and down" ploughing. Rills develop incorrespondance of sow furrows as well as of tire tracks on a steep slope (Tuscany, Italy).Df = pyJlgiR) jf,(F)dF\lR (9)where D^ is the amount of material detached during r^, per unit of surface, p, and V^are, respectively, the mean dry bulk density and volume of the eroded grains,/^ is thefrequency distributions derived by Eqns. 6, 7 and 8.Similar conclusions had already been discussed by several authors as Raudkivi(1976), Yalin (1977), Naden (1987), Torri et al. (1990) and Hearing (1991).Transport capacity of rill flowOnce particles and aggregates have been detached or, in any case, introduced in the

48overland flow, transport begins. This lasts until particles and aggregates areredeposited. The length run by a given grain depends on various factors. Amongthem, the internal forces, the thickness of overland flow water and the particle weightand shape. Turbulences, hydraulic roughness, cross-section variations, and dragcoefficients of grains, etc., make it difficult to find parameters for the system.In fact, the forces acting on the soil grain comprehend gravitational forces thattend to make the particle fall and hydraulic forces, of the kind described by Eqn. 5,where velocity should be considered as the difference between the grain and the fluidvelocity at that point. The presence of forces transversally directed with respect to thegeneral motion direction of the fluid make the grain zig-zag vertically andhorizontally. Sometimes, with bigger grains, the motion takes place by means ofrolling and sliding. Other times, the grain proceeds by a series of successive jumps.The overall picture is furthermore complicated by the difficulties in defining thevalues to attribute to drag coefficients.The above-stated difficulties led many modellists to the application of simplifiedconcepts such as the transport capacity of a fluid in motion, considered as theconcentration of sediments that that system can transport at a steady state. In otherterms, the transport capacity is the maximum quantity of sediments that can betransported by an overland flow having motion characteristics that remain constantin space and time (steady-state flow). In order to give reality to this definition itshould be added that the processes of sedimentation should be just as constant, aswell as the processes of sediment supply. This implies also the constancy of somecharacteristics depending on the type of sediment transported, such as density,dimensions and shapes of particles and aggregates. In some cases also the chemicalcharacteristics of the transported material and overland flow water are important,when the balance between flocculation and deflocculation processes is unstable.If changes in overland flow and erosion are slow in time and space, then it ispossible to define a transport capacity of overland flow. Despite the fact that this israrely the real situation during a natural rain, the use of transport capacity isextremely widespread in modelling and seems to produce reliable results (at least atthe present level of precision).As previously said, the processes making up transport capacity are manifold andcomplex. Therefore, empirical relations are usually utilised. A raisonnee collectionof formulae for transport is given by Covers (1992).Rill erosionThe water of overland flow does not cover the soil surface in a uniform way. On thecontrary, it usually flows in fairly winding microrills (or protorills), of low erosivecapacity, which later join in rills.When the flow becomes more turbulent and therefore more erosive, irregularchannels are formed having a V-shaped transversal section, usually 10 cm wide and5 to 10 cm deep which tend to come together creating a miniaturised hydrographicalnetwork. In recently ploughed fields, which are the areas most subject to this process,the main collectors can deepen their "beds", cutting through the plough layer, in the

most intense cases the cut can affect the whole soil profile until it comes into contactwith the parent material, which is usually more resistant. This phenomenon is calledrill erosion.As previously said, the phenomenon assumes its greatest evidence with the leastprotected soils, i.e., those that have just undergone ploughing or, rather, when theseed bed has just being prepared. The most critical period then falls betweenploughing and the moment when the crops begin to grow (in particular herbaceousvegetation), thus ensuring an adequate cover to the soil. Some ploughing systems {upand down, that is in the direction of the maximum inclination) and particular crops(row crops) noticeably facilitate the development of rill erosion which will exploitpreconstituted courses (the sow furrows) and eventually produce the most conspicuousforms (Hradek, 1989).Very often these forms of erosion reach such dimensions that they can hinder theuse of machines in farming operations; in any case, they are wiped out by thesubsequent ploughing. Evidence of the phenomenon taking place is indirectly givenby the thickening of colluvial deposit belts at the toe of the affected slopes owing tocoalescence of colluvial cones or colluvial fans that are formed in correspondencewith the "mouth" of each rill system (Fig. 18).3.2.3.4 Differential erosionThe morphological evidence of the action of a fluid differs according to theconstitution of the bedrock (rock, sediment or soil) on which the action takes place.On the outcrops of competent massive rocks a uniform smoothing action isproduced (exaration in the case of glaciers, erosion in the case of water, corrasionin the case of wind). On the contrary, on coherent alternating lithotypes the morearticulated the relief the more diverse will be the resistance to grain entrainment{differential erosion, morphoselection (Panizza and Piacente, 1978)).In the particular case of rain-drop impact, the occurrence of differential erosionduring the event is confirmed by a characteristic microrelief of earth pillars (splashpedestals, Fig. 19) due to the soil local protection by coarse elements of variousnature and particle size (pebbles, gravels, vegetal residues, etc.). Soil grains exceeding0.5 cm are removed only with difficulty. If the dimensions are more than a fewcentimetres, also interrill overland flow is incapable of removing them (Poesen et al.,1994). Therefore small earth pillars made up of material protected by the overlyingrock fragment are formed. Differential erosion can take place even if the flow ischannelled. Selective erosion lasts until the surface is completely armoured.3.2.3.5 Subsurface flowWhen a certain amount of rain water percolates into the soil or regolith, water canact both as a solvent, therefore triggering a set of chemical transformations bydestroying some compounds and/or generating new ones, and as a carrier of particles,transferring them from one position to another (leaching, eluviation).Moving under the influence of gravity, these particles will follow vertical paths,in conditions of horizontal surfaces, or more or less inclined along slopes (lateral49

50Fig. 19. "Splash pedestals", an evident consequence of rain-drop impact. The diameter of the coin inforeground is 25 mm.movement). In the latter case and with particular soils and parent material, subsurfaceflow can become sufficiently erosive to trigger removal of particles that are afterwardsevacuated by means of a proper network of underground passages with outlets at thesurface, usually in the higher slope stretch.According to its different dynamics and intensity, various terms are attributed tothis process: tunnel erosion, suffosion, seepage, tunnel-gullying, piping, pseudokarst.The diameter of the water paths can vary enormously, from those a few millimetreswide, due simply to soil porosity, to those properly developed into real undergroundchannels (Fig. 20).Among the main factors generating and keeping the phenomenon active, besidesthe precipitation variability and the vegetational cover discontinuity, shrinkingswellingof soils and of some bedrocks have been recognised; they develop duringthe arid season and are connected with the presence of levels having particular texturecharacteristics (Selby, 1982). These erosion forms develop frequendy also on thesides and heads of ditches or at the crowns of landslides, thus contributing to theirrapid withdrawal.3.2.3.6 Gully erosionWhen cuts reach such dimensions that it becomes impossible to eliminate them

51Fig. 20. Surface collapse due to tunnel erosion in a gypsum-rich colluvial deposit (near Zaragoza, Spain).through normal farming operations, then the term gully erosion is used, sometimeswith the definition of ephemeral gullies for forms which have already suchdimensions as to be considered gully, but which are nevertheless eliminated withspecific farming works.Actually, the term "gully" groups many different types of natural channels suchas the Italian calanco, although with some reservations, the French ravine, theSpanish arroyo, barranco, carcava, the Brasilian-Portuguese vogoroca, the GermanDelle, the Arabic wadi, the Indian hulla. the Swahili donga, etc. This widespread useof terms referring to the same phenomenon is witness to its extension in particularmorphoclimatic environments showing as a common characteristic a certain aridityor, in any case, a net separation between a rainy season and a more or less prolongedarid one (Fig. 21). A typical example is given by the circum-Mediterranean belt.Hudson (1986) defines gullies as ''erosional furrows characterised by very steep

52Fig. 21. Gully erosion on silty-clayey alluvial deposits (Eritrean highlands).slopes and subject to sudden and intermittent runoJf'\ Brice (in Selby, 1982) considersthem as ''recently fanned drainage channels with occasional runoff, steep slopes,vertical or highly inclined head, width exceeding 30 cm and depth over 60 cm'\Any survey must consider these forms of erosion and describe in detail theirfeatures, since their distribution, type and density within each portion of territory canbe assumed as indicators of its state of degradation.Gullies develop in particular situations determined by the concomitance of severalfactors: poor resistance to erosion of both soil and bedrock, high intensity of themeteoric event, conditions of the vegetal cover, slope morphology, land use andmanagement which favour the concentration of water along runoff paths thateventually become permanent.Gullies affect mostly cohesionless or semicohesive materials (loess-like deposits,tuffs, colluvial deposits, poorly cemented marine sediments, etc.). As for their origin.

several hypotheses have been brought forward. Some authors consider them as thenatural evolution of a master rill in a rill system; this situation seems nevertheless totake place only when the affected slope is sufficiently long with morphologicalfeatures favouring the concentration of flow lines. In more general terms, gulliesretreat upslope following a given direction marked by a single headcut (axial gullies,in coarse sediment), or following several headcuts (digitated gullies, in clay loams).The latter type may explain landscapes where erosion has deepened numerous routesthat, after zig-zagging upwards and intersecting each other, have left less erodedreliefs, remnant of a past landscape (Alexander, 1982; Hodges & Bryan, 1982).When a concentrated flow path intersects an earth bank (e.g., sunken lane orroad bank, lynchet and terrace bank, etc.) bank gullies develop frequently (Poesen,1993).A particular type of gully (frontal gull}\ where width largely prevails on length)is usually associated with piping (in loamy sand sediment with columnar structure)which destabihses river walls and banks causing their collapse.Ephemeral gullies form where overland flow concentrates in either naturaldrainage lines or linear landscape elements such as furrows, access roads, etc.(Poesen, 1993). Erosion rates have been observed to vary between 0.9 and 1.2 cm/a(Vandaele, 1993) in the Belgian loam belt, comparable to annual values of rill andinterrill erosion.3.2.4 Aeolian erosionWind is the main factor of aeolian erosion (wind erosion). This kind of erosion isparticularly active in climatic zones with scanty precipitation (with average values of250 to 330 mm/a) distributed in rare rainy events isolated by long drought periodsand, as a consequence, with a discontinuous or totally lacking vegetational cover. Themost remarkable effects and forms are found in concomitance with high temperature,such as in the arid environments of the tropical and subtropical belt.The dynamic processes of aeolian erosion are controlled by the following factors:— soil structure and texture, given that the wind action is highly selective;— soil humidity, especially at its surface, which contributes to keeping particleslinked;— climate, in particular the length of the arid periods with respect to the rainy ones;and— vegetation, that similarly to what happens with rains, reduces wind speedinhibiting its erosive power.Aeolian erosion can be defined as the capacity of wind to entrain and transport looseparticles elsewhere. For a given type of soil, the quantity that can be removed is afunction of wind velocity and surface roughness.Particles are carried with patterns that differ according to their diameter. Threemain types of transport can be identified:— suspension, affecting the smallest particles (generally less than 0.1 mm) that canbe carried even over long distances, as it happens during dust storms'.53

54— creep, a kind of movement that compels larger particles (0.5 to 2.0 mm) to"creep" or roll at the surface, moved by the power of wind or pushed by otherparticles;— jumping, that is by successive "jumps" affecting those particles having dimensionstoo large to be carried in suspension or too small for rolling (roughlybetween 0.05 and 0.5 mm); their movement takes place by means of a series ofrebounds having curved trajectories, whose height is proportional to the particlemass.Let us see some of what has been just described in the light of the equations rulingwind shearing and lifting forces, i.e., of the equation already described for a fluid inmotion. As already stated, laminar wind flow does not exist. This makes thingssimpler as only Eqns. 3 and 6 are to be examined. It comes out clearly that highroughness values reduce wind erosivity because high velocities are attained at moreelevated height values.Differently from water erosion, wind erosion is mainly due to lift detachingforces. This depends on two factors: firstly, wind produces an intense lift. Secondly,soil is mainly eroded when it offers a minimal resistance to detachment. The lattersentence means that soil is more erodible when it is dry, when grains are loose (nocohesion) and when friction is nil. Consequently, resistance to grain detachment isgiven by grain weight. This situation makes fine sand and silt, the grain-size classesmore prone to wind erosion.Grain transport by saltation causes a peculiar type of detachment. When a windtransported grain is impacting the soil surface a large impulse is released on a verysmall impact area and other grains are consequently displaced. As soon as thedisplaced grains are ejected some centimetres above the ground surface they are moreeasily entrained by wind because it blows more intensely (wind velocity increaseswith height, as stated in Eqn. 3). A detailed study of the physics involved in winderosion in desert environments was made by Bagnold in the late thirties, early forties(see Raudkivi, 1976; chapter 4).Forces depend on wind velocity (Eqn. 6), which, in its turn, depends onroughness. Surface roughness is here made of soil grain roughness, clods or otherman-made soil surface structures, vegetation (including trees), fences, some elementsof the landscape, etc. It is evident that, controlling surface roughness, e.g.. via fences,wind speed can be controlled and consequently wind erosion, to a certain extent,modified.The effects of wind deflation are basically the following ones:— soil thinning at the expense of the overlying horizons;— indirect soil enrichment with coarser material since, as discussed in chapter 3.3,only the finer fractions are removed; the process comes to an end when a propererosion pavement is formed, as it happens in several desert areas; and— general levelling of the soil surface since the material transported can deposit intodepressions filling them and reducing roughness.

553.2.5 Models for evaluating water erosion3.2.5.1 General overviewIn the previous chapters an overview was given of the erosive processes and therelated forms. Before surveying models suitable for predicting water erosion let usfirstly discuss how the various processes can be assembled and give some nomenclature.In the previous chapters the actions of overland flow and rain drops in theproduction and transport of sediments were considered. In order to assemble them itwill be necessary to apply widely the law of conservation of matter (or continuityequation).Let us consider a rill segment of unitary length, width vv and cross-section A. Thequantity of sediments coming out of the system minus that going into it must equalthe quantity of removed or deposited sediments within the segment considered.Let us first consider what happens outside the rill segment. The variation ofintensity in the sediment flow (in terms of mass) between the outlet downstream andthe input upstream of the rill segment is given by dS / dx. From the interrill zones(one to the right and one to the left) 2^, material per unit of length arrives, which isdetached by the drop impact and carried by overland flow. The dS/dx - le- quantitymust equal the quantity of material which is temporarily produced, deposited orprovisionally stored within the rill segment. If 3(p,^) / dt is the mass correspondingto variations in rill volume (where p, is the dry soil bulk density) and d{^cAJ / dt isthe variation of instant storage within the segment (where A^, is the transversal sectionwetted by rill, p the density of the transported grains and c is sediment concentrationby volume), then the law of mass conservation is:^^ = 2e ^ 9(pA) _ dipcAJ^Q^This equation, already used by Culling (1963), Meyer & Wishmeier (1969), Bennet(1974), etc., is known as continuity equation. It is valid, with opportune variations,for diffuse and concentrated flows of both sediment and water. When sediment andwater continuity equation are considered together, they assure the correct transfer ofthe flow and sediment among contiguous cells of any distributed model (see forward).Practically, the continuity equation, together with transport capacity, detachmentand sedimentation equations, ensures the linking of the different processes duringerosive rains.The same equation is used also for transferring sediment along a slopeuntil the toe-slope or a draining channel is reached.Now that the main mathematical tools for describing sediment production areavailable, models can be assembled. Obviously existing models do not describe fields,slopes or basins in the same way. In particular, a model is a simplified representationof nature and its performances depend on the way in which it is structured, theequations it uses, etc. Chow (1972) divided hydrological models into eight categories.

56We will quickly examine the most important ones. In order to understand differencesbetween models let us exemplify considering a basin as the object to which anerosion model is applied. The model is lumped if the basin (or large portion of it) istreated as one unit. In this case, the basin characteristics are necessarily simplifiedbecause the unit is treated as a uniform homogeneous system. This strongly reducesthe possibility of controlling what happens inside the basin and model outputs arenecessarily broad approximations if the basin is scarcely uniform.Distributed models subdivide the basin into a large number of small cells.Sediment is routed from one cell into another (using equations like Eqn. 10) anderosion and sedimentation can be located inside the basin. In this case each celldescribes a sufficiently uniform and homogeneous area so that parameter values havereasonable chances of being well representative of reality. In any case, since there areparameters that often vary significantly even inside a single cell, model equationsshould be able to deal with spatial variability, introducing stochastic behaviour withinpredictions. Usually this is not the case. Let us consider a simple example of aprocess that takes place when a given threshold is overcome. Concentrated overlandflow can dig a rill only when its shear velocity is larger than a given value whichdepends on soil cohesion (Rauws & Covers, 1988). Unless the model is distributedand each square metre is represented in a single cell, several rills may develop insideeach grid element. Spatial variability of soil cohesion will allow rill formation firstin a spot, later in another. The model will not allow a progressive increase in rillnumbers because it deals with each grid element as a whole, abruptly passing froma no-rill situation to the opposite one. This type of model, where situations are alwayswell determined, is said to be ''deterministic" while the one that considers spatialvariability is said to be ''stochastic".The equations chosen for representing processes and rates inside a model can bebased on either empirical relationships between variables or physically basedformulae and algorithms. Obviously, an empirical model must always be tested,sometimes even partially modified, before being used in areas too different fromthose where it was developed. Physically based models have a better chance ofreasonably approximating reality when used elsewhere.Models presented in the years 1960—1980 are mainly deterministic and lumped,and use physically based equations only rarely. More recent models are distributedand physically based equations are frequently used. As an offset, however, it is morecostly to feed data and to run them because of the increased number of parametersand the length of the their codes.Among the many water erosion models in use nowadays, EPIC (Srinavasan &WiUiams, 1996) and GLEAMS (Nicks, 1996) must be mentioned. New models areWEPP (Nearing et al., 1989), KINEROS (Woolhiser, Smith & Goodrich, 1990),EUROSEM (Morgan et al., 1996), LISEM (De Roo et al., 1996) and the MEDALUSseries (Kirkby, 1996a,b).Let us try to understand what type of parameters are needed for assembling amodel able to describe soil loss. We have seen that the main detaching agent israindrop impact. This means that we need equations able to account for splash effect

correctly. This is usually achieved through a correct estimation of drop kineticenergy, drop interception by canopy cover, intercepted water subdivision in"permanently" held water, stem-flow and new drop production by canopy (seeBrandt, 1989, 1990; Styczen & Hogh-Smith, 1986).The erosiveness of the storm is also due to overland flow detachment andtransport. This means that the model must generate runoff, then make it flow andcumulate along the slope. This means that slope angle and length must be known.Also, all the soil and vegetation properties that influence water infiltration (e.g.,porosity, aggregate stability, surface depression storage, etc.) or resist runoff flow(surface roughness) are needed.The Universal Soil Loss Equation (USLE, Wischmeier & Smith, 1975) is a simplemodel where those parameters are taken into account. This is a deterministic,empirical and lumped model. Storm erosiveness is found by means of 3 factors: 1)rain erosivity, where drop kinetic energy is multiply by a sort of magic factor, i.e.,maximum rain intensity in half an hour; 2) slope length; and 3) slope angle factors.Effects of vegetation and management are accounted for with two other factors. Thesoil erodibility factor includes all the soil characteristics more or less relevant todefine soil resistance to detachment and transport and soil hydrological behaviour.This model was obtained using data collected in field plots. It gives estimates ofmean annual soil loss over a 20-year period and should be applied to uniform,homogeneous fields with no gully erosion. Its use for shorter periods is not correctand should be avoided.A model with opposite characteristics is EUROSEM, which is deterministic anddistributed and uses many physically based equations. It was explicitly written inorder to be run on single rain events. In between these two extremes, the WEPPmodel describes what happens between one event and the next. It can therefore beused for assessing erosion over longer periods, at least a few years, althoughmaintaining a high temporal resolution. A model that can compete with both theprevious ones is MIKE-SHE (Danish Hydraulic Institute, 1993), associated with theerosion functions of EUROSEM, because it is based on an excellent hydrologicalmodel with a continuous simulation over indefinitely long periods.In some cases erosion models, able to run over periods of thousands of years maybe necessary. In this case previously listed models are not suitable because parameters,that are relevant for a given time span, can lose their meaning at other timescales and become sources of errors. A model for long term erosion evaluation waspresented by Hallet & Putkonen (1994) for a study comparing the age of somemoraines. Here the parameter of major interest is linked to topography, which isrepresented in terms of the length and slope inclination of moraines. In particular, asimple sediment flow model is applied which is expressed by means of the followingequation:57

58S = a(l + bx) —dx(11)where a and b are site-specific constants, x is downslope distance and z is thealtitude.In this case precipitation does not appear any longer as an explicit term: the timeinterval considered is so long that the characteristics of single rainfalls totally losetheir importance. Only mean precipitation amounts over very long times areimportant. This fact, though, is reflected only on a and b and is important only whenit is necessary to compare environments with definitely different climatic histories.Equation 11, together with the mass conservation one (Eqn. 10) leads to thefollowing expression:dz .1— = a(\dtbx)dx'^ab dz_31(12)where the storage variation term of Eqn. 10 is neglected since it is not significant inthis case.The use of Eqns. 11 and 12 permitted Hallet & Putkonen (1994) to solve aconflict about the dating of some moraines. The conflict arose following datingcarried out by means of cosmogonic isotope analysis and stratigraphy-basedconsiderations. The first technique allows the age of exposition to the surface of acertain rock to be evaluated. Nevertheless one should also consider the surfacerejuvenating processes due to erosion.3.2.5.2 De Ploey's erosion susceptibility modelFrom 1987 until 1992, De Ploey (1989, 1990) developed a rather interesting modelwith a wide range of applications and intrinsic simplicity. The model was developedstarting from Eqn. 13 relative to erosion linked to the upstream movements of littlewater falls found in rills and gullies (Fig. 22). The basic idea was that of consideringthe volume V of the eroded material proportional to the total mechanical energyoriginal surfaceplunge poolFig. 22. Sketch illustrating a (fictitious) longitudinal gully profile: small falls and headcut retreat rate arethe basic idea supporting De Ploey's (1990) model.

(potential and kinetic) of the water at each fall. This simplification resulted in thefollowing equation:59V{T)= EJ'^q^it) gh^it) -u-{t)\dt(13)where:T, t = time;E = soil susceptibility to headcut erosion;g = gravity;Qi = discharge rate at the i-th fall;hj = fall of the i-th height.De Ploey (1989) presented a simplified version of Eqn. 13 which is valid for a singleheadcut. It can be derived from Eqn. 13 by simply substituting the integral and thesummatory with a total height h and a total discharge QT, where Q is the meandischarge rate over the time span T. Also u must be changed with a mean flowvelocity U over the period T. Using such simplifications it follows that:V = EQT ghU'^ (14)Of course Eqn. 14 is an approximation but it contains two terms that represent twodifferent types of erosion. Let us suppose that diffuse interrill and rill erosion aredominant. Then the term linked to potential energy is negligible with respect to thevelocity term. Hence Eqn. 14 may be rewritten neglecting gh. The opposite is truewhen gully erosion is dominant or when landscape is characterized by badlands. Heregh dominates. In the former case Eqn. 14 needs a long series of assumptions mainlydue to difficulties in handling mean flow velocity. On the contrary, the latter case canbe easily applied, hence it will be treated in some detail in the following paragraphs.Equation 14 then becomes:E =APTgh^(15)where h^^ is the depth of the gullies found in a catchment of area A (more precisely,A is the gully catchment or the area pertaining to a given gully system) and totalannual precipitation P has replaced Q. In this case time units are years.If we consider that V = A^jh^ (where A^ is the surface occupied by gullies), aftersubstitution in Eqn. 15, the following is obtained:

60A G (16)Equation 16 is easy to handle as the ratio between the two areas is measurable bothfrom aerial photographs and field surveys. The annual mean precipitation can beestimated with a certain accuracy (ratings with uncertainties around 10—15% can beobtained). It is therefore possible to assess erosion susceptibility for gullies once thervalue is known. The same technique is valid for assessing badland areas, where theratio between the two surfaces is close to 1.From the data examined by De Ploey (1992), it results that in the case of gulliesand badlands E varies according to the values illustrated in Table 7.It should be noticed that none of the classical elements, such as inclinationintervals, slope lengths and relief energies appears in Table 7. Although some of theelements linked to the pedotype appear, the effect of vegetation is dominant.3.2.5.3 PSIAC modelOne of the methods allowing all effects of soil erosion to be evaluated (consideredas the quantity of removed material and destined to sedimentation) in hydrographiccatchments of a certain extension, located in prevalently mountainous environmentsand characterised by high energy relief, is that applied in 1968 by the US PacificSouthwest Inter-Agency Committee (PSIAC) in the south-western territory of theUnited States (Table 8).The factors that the PSIAC method adopts as fundamental for the calculation ofthe sediments produced in a certain area, and therefore for the assessment of potentialerosion within its boundaries, are the following ones:1) lithology: composition, cohesion degree, bedrock alteration and fracturing;2) pedology, soil typology and physicochemical characteristics;3) climate: temperature regime, but mainly frequency, duration and intensity ofrainfall.4) runoff: flow regime both along slopes and riverbeds;TABLE 7Erosion susceptibility values for gullies and badlands (after De Ploey et al.. 1995)E values (s/m')10""*—5• 10"''3-10~^—10~^10"^—3-10"^DomainsBadlands in different climatic belts, cultivated land; steppe areas with savanna,woodland; degraded grasslands and savannas (often due to overgrazing).Partly degraded steppe woodlands or savannas with duricrusts including lateritecappings; areas underlain by soils with a high absorption capacity (sandy soils,chernozems); areas with mixed farming: arable land, prairies and forested slopes.Areas with occasional gullying, predominantly thalweg gullying; forestedcatchments with dispersed cultivation; perennial grasslands and savannawoodland with appreciable runoff coefficients during storm events.

61TABLE 8Scoring table of the PSIAC modelSedimentyield levelLand factors1. Lithology(A)2. Soils(B)3. Climate(C)4. Runoff(D)High(10)(10)(10)(10)a) Marine shalesand relatedmudstones andsiltstones.a) Fine texturedeasily desperded;saline-alkaline;high shrink-swellcharacteristics.b) Single grainsilt-fine sand.a) Storms of severaldays durationwith shortperiods of intenserainfall.b) Freeze-thawoccurrence.a) High peakflows per unitarea.b) Large volumeof flow per unitarea.High tomoderate(7.5)(7.5)(7.5)(7.5)Moderate (5) (5) (5) (5)a) Rocks of medium a) Medium textured a) Storms ofhardness.b) Moderatelyweathered.c) Moderatelyfractured.soils.b) Occasionallyrock fragments.c) Caliche layers.moderateduration andintensity,b) Infrequentconvectivestorms.a) Moderate peakflows.b) Moderatevolume of flowper unit area.Moderate tolow(2.5) (2.5) (2.5) (2.5)Low (0) (0) (0) (0)a) Massive hardformations.a) High percentageof rockfragments.b) Aggregatedclays.c) High content oforganic matter.a) Humid climatewith rainfall oflow intensity.b) Precipitation inform of snow.c) Arid climate,low intensitystorms.d) Arid climate,rare convectivestorms.a) Low peak flowsper unit area.b) Low volume ofrunoff per unitarea.c) Rare runoffevents.(Continued)

62TABLE 8 (Continued)Land factors5. Topography 6. Ground cover 7. Land use(E) (F) (G)8. Upland erosion 9. Channel erosion(H)(I)(20) (10) (10) (25) (25)a) Steep upland Ground cover a) More than 509^- a) More than 50% a) Eroding banks conslopesin ex- does not exceed cultivated. of the area tinously or at frequentcess of 30%; 20%: b) Almost all of characterized by intervals with largehigh relief;little or nota) vegetationsparse; little orarea intensivelygrazed,rill and gullyor landslidefloodplain development.no litter; c) all of area erosion.b) no rock in sur- recently burned,face soil.(15) (5) (5) (17.5) (17.5)depths and long flowduration,b) Active headcuts anddegradation intributary channels.(10) (5) (0) (10) (10)a) Moderate up- Cover not ex- a) Less than 25% a) About 25% of a) Moderate flow depths,land slopes ceeding 40%: cultivated.the areamedium flow duration(less than a) Noticeable b) 50% or less characterized by with occasionally20%). litter. recently logged. rill and gully eroding banks or bed.b) Moderate fan c) Less than 50%or landslideor floodplain intensively erosion,development. grazed.b) Wind erosiond) Ordinary roadand other constructions.with deposition.(5) (-5) (-5) (5) (5)(0) (-10) (-10) (0) (0)a) Gentle upland a) Area comple- a) No cultivation, a) No apparent a) Wide shallow chanslopes(lessthan 5%).b) Extensivealluvial plain.b) No recent logging.c) Low intensitygrazing.signs of erosion.tely protectedby vegetation;rock fragments,litter;little opportunityforrainfall toreach erodiblematerial.nels with flat gradient,short flow duration.b) Channel in massiverock, large boulders orwell vegetated.c) Artificially controlledchannels.

63TABLE 9Classes of probable sediment yield, resulting from the summation of scores assigned to each erosion factor(example from Southwestern USA, USDA, 1968)Values Class mVha/year>100 I >14.2975-100 II 4.76-14.2950-75 III 2.38-4.7625-50 IV 0.95-2.380-25 V

643.3 Landslide hazard*=^by Alessandro PASUTO and Mauro SOLDATI3.3.1 IntroductionSeveral papers and detailed reviews dealing with landslide hazard have been recentlypublished (Hansen, 1984; Varnes, 1984; Hartlen and Viberg, 1988; Brabb, 1991;Corominas, 1992; Jones, 1992; Hutchinson, 1995). An important incentive hascertainly been given by the International Decade of Natural Disaster Reduction -IDNDR - (1990-2000), proclaimed by the United Nations', during which differentworking groups have been set up, such as the International Landslide ResearchGroup, aiming at the preparation of a proposal for worldwide hazard maps (Brabb,1993), and the International Geotechnical Societies' UNESCO Working Party onWorld Landslide Inventory which is contributing to the establishment of a WorldLandslide Inventory by suggesting standard terminology for landslide investigation(WPAVLI, 1990; 1991; 1993).Most of the authors above quoted feel that landslide hazard is generally neglected,more emphasis being given to other types of hazards such as seismic and volcanichazards. It has been estimated that every year about 225,000 lives are lost becauseof natural events in general (Burton et al., 1978), among which several massmovements causing many casualties (for a more comprehensive review of theseevents see Eisbacher & Clague, 1984; Hansen, 1984; Brabb, 1991; Gares et al.,1994). The fact that landslide hazard is usually underestimated is even moreunfortunate, since slope movements are usually more easily predictable andmanageable than earthquakes, volcanic eruptions or hurricanes. Actually, besideshigh-magnitude mass movements which occur quite seldom, there is a huge numberof medium to small sized landslides which are so widespread that the related cost forhuman society is even higher than that of catastrophic events. The losses due to lowmagnitude,high-frequency events is also generally increasing, especially indeveloping countries, because of human activity which, on the one hand, tends toincrease landslide hazard (road cuts, quarries, etc.) and, on the other hand, favoursvulnerability situations. Jones (1992) stated that landsliding is generally poorlyunderstood by nonspecialists and for this reason underestimated in developmentprogrammes. In addition, Varnes (1984) noticed that a considerable proportion ofdamage and casualties generally related to earthquakes and hurricanes (including alsovolcanic eruptions) is actually to be ascribed to landsliding which occurs as an effectinduced by these phenomena. A significant example is that of the 1970 earthquakein Peru, which claimed 70,000 lives, 20,000 of which in a debris avalanche detachedfrom the north peak of Nevado Huascaran (Plafker & Ericksen, 1978).The correct interpretation of landslide hazard and consequently the optimisationof the interventions to be carried out in order to mitic^ate the loss of human lives and'UN resolutions 42/169 and 44/236 (for further details see Scott. 1992).

economic assets, depends on some general considerations. First of all gravitationalphenomena should be considered as an effect of natural landscape evolution. It is infact the interaction of these phenomena with man's activities and structures thatcauses casualties and damage. Indeed, on the one hand, population increase hasdetermined a greater need for natural resources and space available for humanactivities and, on the other hand, constant technological progress and the improvementof living standards have caused remarkable changes in natural environments;as a consequence, natural events such as landslides have had increasingly seriousconsequences on man's life and activities.Unfortunately, it should be pointed out that the terms Hazard and Risk are oftenused rather ambiguously. After a general definition of the various aspects ofgeomorphology given by Panizza (1987), Hartlen & Viberg (1988) specified that"hazard is confined to the expected occurrence of landslides, while risk involves thedamage expected to be caused by landslides (lives lost, cost of damaged buildings orfacilities etc.)". Therefore, it becomes clear that landslide hazard should be adequatelyassessed in order to give a feasible prediction of the level of risk.Varnes (1984) maintained that among all natural hazards, landslides are thosemost easily foreseen and mitigated. For this purpose this Author defines the mostfundamental principles on which landslide hazard assessment is based according tothe following statements.~ 'The past and present are keys to the future". This means that, according touniformitarian principles, areas characterised by geological, geomorphological andhydrological conditions which favoured or triggered landslides in the past, or aredoing so in the present, are very likely to be subject to failures also in the future.Nevertheless, the absence of past and present failure does not mean that landslideswill not take place in the future. Thus, detailed investigations on the physicalenvironment and on the spatial and temporal occurrence of landslides are ofprimary importance in terms of landslide hazard assessment. However, the effectsof human activities and climatic changes, which are variable with respect to whathas been mentioned above, should always be taken into account.— "The main conditions that can cause landsliding can be identified". An understandingof the processes involved in slope movements is fundamental and presenttechnology in most cases allows these causing conditions to be identified.— "Degrees of hazard can be estimated". This means that, once the factors and theprocesses involved are known, qualitative or semiquantitative assessments of theircontribution to landsliding can be made.To the three statements above quoted, Hutchinson (1995) adds a fourth:— "The various types of landsliding can generally be recognised and classified, bothmorphologically, geologically and geotechnically". This Author emphasizes inparticular the importance of geotechnical aspects which are very often neglectedor overlooked in this kind of investigation.The definition of landslide hazard and risk should therefore be based on a preciseknowledge of landsliding phenomena, in terms of type, mechanism and evolutioncharacteristics as well as the main factors which have conditioned or could condition65

66their temporal and spatial development, including the rate of human activities in thearea studied.This chapter deals with the methods and techniques which can be utilised for theassessment of landslide hazard. It should be underlined that the term landslide is usedin its most general meaning, that is: ''the movement of a mass of rock, earth or debrisdown a slope under the force of gravity" (Cruden, 1991) and that only subaerialphenomena will be discussed.3.3.2 Types and causes of landslides3.3.2.1 General aspectsWhen a study of mass movements is enterprised, which also aims to define landslidehazard, it is of paramount importance to use clear terminology which can beuniversally understood also by nonspecialists (IAEG, 1990). It is therefore importantfor these phenomena to be immediately identified and subdivided according to thegeomorphological and kinematic characteristics directly observable.In scientific literature, there are several ''classifications"' regarding to slopemovements which have been proposed since the beginning of this century. Theseoften complied with the needs of various authors but more recently an effort has beenmade to use the least ambiguous terminology. Most recent classifications try toemphasize both the processes leading to the development of a landslide and thematerials involved; others are based on morphology, landslide mechanism,deformation velocity, causes of movement, geometry of the failure area and thedeposits, age, etc.This paper does not aim to describe the numerous "classifications" proposed butparticular attention will be given to the two most commonly accepted, that areillustrated and subsequendy modified by Varnes (Varnes, 1958; 1978; Cruden &Varnes, 1996) and Hutchinson (Hutchinson, 1968; Skempton & Hutchinson, 1969;Hutchinson, 1988). Both authors use the type of movement as a discriminatingelement. Basically, what changes is the kind of approach: whilst the former tries toemphasize the aspects linked to the result of the movement, the latter analyses theconditions that lead to failure. Essentially, the scheme proposed by Varnes is easierto apply and requires less experience, whereas the one proposed by Hutchinson ismore complex and based on an approach more from the engineering viewpoint.Varnes proposed his first subdivision in 1958. He distinguished gravitationalphenomena as falls, slides, subdivided into glides (with translational slip surface) andslumps (with rotational slip surface), flows and complex. The first two types werefurther subdivided according to the material affected, which could be either rock orsoil; flows were in turn subdivided on the basis of particle size distribution and thewater content of the loose soil. Subsequent elaborations of this scheme were carried'It should be specified that the use of the term "classitlcation" is to be discouraged when referred to acomplex natural process which could hardly be inserted into the rigid scheme of an excessively detaileddistinction (see: 1.3).

out in 1978 and 1996 and at the moment this subdivision is universally accepted.The main criterion used by the author in the identification of the landslidecategories is the type of movement, whereas a further subdivision is made on thebasis of the type of material. As for the type of movement, five categories arerepresented: falls, topples, slides, spreads and flows. On the other hand, the materialsare divided into two types: rock and engineering soil; the latter is further subdividedinto debris and earth. In this way a landslide can be described by means of twowords: the first one describing the material and the second one the type of movement(Table 10). These types are distinguished as follows.Fall: Generally the mass is detached from a very steep slope along a surface onwhich little or no shear displacement takes place. It occurs mainly in the air and thephenomenon includes the material's free fall, saltation, bouncing and rolling.Topple: The movement is due to stresses which cause a toppling momentum arounda rotation point situated below the centre of gravity of the rock mass affected. Thephenomenon can evolve into either a fall or slide.Slide: The movement takes place by means of a shear displacement along one ormore surfaces or along thin zones of intense shear strain. Either rotational slides(slumps), in which the movement occurs along a curved and concave failure surface,or translational slides, in which the mass moves along a plane or undulating surface,can be found.67TABLE 10Landslide types (according to Varnes, 1978 and Cruden & Varnes, 1996)Type of movementType of materialBedrockEngineering soilsDebrisEarthFallToppleSliderotationaltranslationalLateral spreadFlowComplexRock fallRock toppleRock slumpRock slideRock spreadRock flowDebris fallDebris toppleDebris slumpDebris slideDebris spreadDebris flowEarth fallEarth toppleEarth slumpEarth slideEarth spreadEarth flow"Combination of two or more principal types of movements (e.g., rock fallavalanche)""Mudslide (British usage)

68Spread: These are movements characterised by lateral spreading, typical of a jointedrock mass and often combined with subsidence occurring in softer, less competentunderlying materials; sometimes it is not possible to recognise a basal slip surface norwell defined ductile deformation zones.Flow: The phenomena characterised by continuous movements in space fall withinthis class; in them the shear surfaces (or thin zones of distributed shear) are shortlived,closely spaced and not usually preserved. From the kinematic standpoint themovement could be compared to that of a viscous fluid.Varnes foresaw a sixth type of movement called «complex» which is the result of thecombination of two or more of the five classes above illustrated. In this regard, thespecification introduced by Dikau et al. (1996) seems opportune: ''... all landslidesinvolve more than one type of movement either acting concurrently in different partsof the failure (compound' landslide) or evolving downslope or over time into adifferent process (i.e., initial failure to subsequent deformation and complexlandslides)".In their latest revision of this ''classification", Cruden & Varnes (1996) stated:"the sixth type proposed by Varnes (1978), complex landslides, has been droppedfrom the formal classification though the term «complex» has been retained as adescription of the style of activity of a landslide". Moreover, other attributes areintroduced so that the definition becomes more elaborate but more information is thusavailable on the gravitational movement. The type of landslide is described by aseries of adjectives placed in sequence which provide information about the activity,the rate of movement, the moisture content, the material and type of movement (e.g.,active rapid wet rock slide).On the contrary, the classification proposed by Hutchinson (1988) is much morecomplex since it: "... pays regard primarily to the morphology of slope movements,with some consideration being given also to mechanism, material and rate ofmovement". It ranks landslides into eight large groupings (rebound, creep, saggingof mountain slopes, landslides, debris movements of flow-like form, topples, falls andcomplex slope movements), in turn further subdivided.Recently, a new subdivision (Table 10) which takes into account both Varnes's(1978) and Hutchinson's (1988) classifications has been proposed. It was developedwithin the framework of a EU funded project on landslides in Europe", is of simpleapplication and appears very suitable for landslide studies in Europe (Dikau et al.,1996).As regards the causes of mass movements, they can be divided into two largecategories (Terzaghi, 1950; see Fig. 23):'Composite according to Cruden & Varnes, 1996.'EPOCH Programme, 'The temporal occurence and forecasting of landslides in the European Community"(CT. 90 0025) (Casale et al., 1994; Soldati, 1996).

69causes reducingmaterial's shear strengthcauses increasingshear stressesgeological factors(llthology and tectonics)''• morphological features{slope geometry, slopeangle, aspect etcclimatic conditions .(precipitations, freeze-thaw icycles etc.) Iremoval of lateralsupport(undercutting, excavations etc.)tectonic activity(uplifts, seismicshocks etc.)Fig. 23. Internal and external causes of landslides.— Internal causes: they lead to the failure of the slope without the intervention ofperceptible changes on the surface; they are in fact causes which reduce themateriars shear strength.— External causes: they determine an increase of the shear stresses by means ofmore or less evident modifications of slope morphology.Naturally, the factors belonging to these two categories can be combined to varyingextents so they do not fit in with any particular classification. Let us now considermore in detail the internal causes which condition the stability of a slope.3.3.2.2 Internal causesGeological factorsThey are given by all the primary characteristics that make up a slope, first of alllithology which includes both the rock's mineralogical and textural composition andits structure. Among rock types more easily subject to disarrangement phenomena,clays are to be quoted, both those of primary origin and those derived from themeteoric weathering of volcanic materials. Argillaceous soils are particularly subjectto instability phenomena such as flows. Also the structure of the formation involvedis very important. For example, formations made up of alternating layers, such asflysch, where rock types showing ductile mechanical behaviour overlie brittle rocks,are usually subject to widespread and vast landslides. Also discontinuities, bothprimary (bedding planes) and secondary (schistosity and foliation planes), play animportant role in the materials' geomechanical behaviour especially with regard tomass movements such as the attitude of layers (low-angle dip-downstream beds willgenerally be more prone to sliding than dip-upstream levels).Of course, all these intrinsic characteristics of the materials can undergo changesof varying intensity and rapidity during the stages of a slope's geomorphologicalevolution. In fact, certain kinds of processes which to some extent modify thematerials' physicochemical characteristics can take place, causing a consequentdecrease of shear strength. Some processes such as weathering, softening, hydration.

70exsiccation, etc., may require a long time and induce changes of the shear resistancewhich in some cases can be considered cyclical. Others such as remoulding,liquefaction, fluidification, develop much more rapidly and can lead to the collapseof an entire slope. These processes can have both natural (precipitations and snowmelt) and man-induced causes (deforestation, creation of reservoirs, diversion ofwatercourses, etc.).In any case the final result is a progressive deterioration of the slope leading todecreased cohesion of the materials that make it up. As a consequence, hydraulicconditions which in the past had caused only small movements could, if theweakening process continues, result in a slope failure (Fig. 24).Among geological factors, also the tectonic history of the slope should be considered.The presence of important structural discontinuities such as faults, fractures,cleavage, joints, slickenside or even folds, fault-folds, etc. induce an intrinsic weaknessof the internal bonds thus making the slope particularly prone to landsliding. Thecontrol exerted by tectonic factors is particularly important in large landslides ordeep-seated gravitational slope deformations (Dramis & Sorriso-Valvo, 1994).Morphological featuresThey include first of all the slope geometry, i.e., its height, length, shape, slope angleand aspect. The influence of the slope gradient is quite evident with respect tostability; indeed, very vast and steep slopes are more predisposed to disarrangement;on the other hand, even low-angle slopes can be subject to particular types oflandsliding such as, for example, flows.Climatic conditionsAlthough there are several climatic parameters playing some role in the starting oflandslides, the most important one is without doubt rainfall. Rainfall should beconsidered not only as the triggering pluviometric event (considering therefore onlyits intensity) but also as the amount of rain falling and accumulating during a certain^landslideTimeFig. 24. Progressive decrease of the factor of safety against time. Temporary decreases of the factor ofsafety without slope failure may be due to exceptional rainfall and snowmelt. Slope failure takes placewhen the factor of safety descends below 1 (modified after Terzaghi, 1950).

period (considering also the length of time). If the percolation velocity is low, therainfall duration assumes predominant importance for the triggering of the movement;on the contrary, in soils characterised by high hydraulic conductivity the functionplayed by rainfall intensity becomes of paramount importance (Campbell, 1975). Therole of water mainly consists of an increase in porewater pressures caused byvariations of the groundwater level. The cyclicity of these changes is a determiningfactor in weakening the internal bonds of the materials making up the slope. Theinfluence of the various types of rainfall will of course be different according to thetype of landslide. Therefore, intense and time-concentrated rainfall will be particularlyeffective in triggering spatially limited movements such as debris flows, soil slips,mud flows (see also 3.6.14), whilst prolonged precipitations could mainly give riseto slides and complex phenomena.Several studies analysed the relationship between rainfall and soil disarrangementsin order to identify a pluviometric threshold above which landslides occur. At thepresent level of knowledge no agreement has yet been reached about this. Nevertheless,it seems that this threshold could be related to the mean annual rainfall of thearea in question (Govi & Sorzana, 1980). Another important aspect concerns the typeof precipitation. In fact, the time interval whose cumulative rain amount can causedisarrangements was defined as "effective rain period" (varying according to theauthors from 15 to 40 days), whereas the maximum rainfall occurring in a timeinterval of 1 to 3 days before the starting of disarrangement processes, was definedas "peak rainfall" (Friz et al., 1986). Therefore, the ratio between these twomagnitudes conditions the development and type of slope movements. Even if thespecific literature is very exhaustive, there are nevertheless margins of uncertaintieson the applicability of these correlations in terms of forecast.3.3.2.3 External causesAs regards external causes which result in an increase of shear stresses, thoseprocesses giving rise to changes in slope geometry, mainly with an increase of thegradient, should first be considered. Among these processes the following areparticularly important: undercutting due to the erosion of a watercourse or to theexcavation for road construction, the exploitation of quarries or open pits, etc. Slopegeometry can change also because of phenomena taking place underground: forexample, the formation of large cavities owing to mineral chemical solution orsqueezing out of underlying ductile materials.Overloading can be another phenomenon inducing an increase of applied shearstresses. This can happen owing to both natural causes, such as soil imbibition byrain or snow melt, accumulation of materials from volcanic eruptions, avalanches,debris flow or other movements, types of vegetation, etc., or human activities as, forexample, in embankment construction, buildings or other structures, in accumulationof tailings from mines and pits or in lacustrine basins or artificial reservoirs.Also the removal of lateral support exerting a counterthrust on the slope could bea cause of unbalance. For example, a glacier's withdrawal is one of the most frequentcauses which determined vast postglacial landslides in the Alps. To this category also71

72tectonic phenomena such as activities along fault planes and subsidence should beascribed, besides gravitational movements themselves. It is, in fact, obvious that thedetachment of a portion of slope induces in the in-place material a redistribution ofthe stresses which can eventually cause a new movement.Another factor which can favour the development of mass movements is lateralpressure. It can be exerted by water percolating into joints or by ice; also swellingsdue to hydration could induce considerable lateral pressures as well as the mobilisationof residual tectonic stresses.Tectonic activity can be a direct cause of slope movements in the case of regionaltilting or uplift. Also in this case the effect of the tectonic process takes placeessentially by means of an increase of the slope gradient. Finally, superficialdeformations induced by volcanic processes can increase the shear stress within aslope also locally.A particular discussion should be reserved for seismic shocks and other transitorystresses such as vibrations induced by operating machines, explosions, rock falls, etc.These events can cause both a reduction of the materials' shear strength and anincrease, although temporary, of shear stresses. The former can be exemplified byphenomena such as liquefaction induced by sudden, cyclic increases of porewaterpressures with a consequent instantaneous decline of the soil's resistance and thecollapse of the slope. This happens most frequently in saturated cohesionless mediumfinematerials such as sands, silts, clays, etc. The increase of shear stresses is, on thecontrary, linked to both the accelerations to which the materials are submitted duringvibrations and the temporary increment of the gradient angle in unstable slopes, since:''... it is known that on metastable slopes a change of gradient angle by tens ofseconds may cause the disturbance of their equilibrium and the movement of potentialand stable landslides and collapses" (Solonenko, 1977).Finally, the effect of vegetation on slope stability may be twofold: sometimes itpromotes stability by reducing the action of climatic agents on the slopes, protectingthe soil from precipitations, wind and sunshine: it retains a considerable amount ofrain water by means of leaves, branches, etc., and eliminates water through evapotranspiration;runoff and erosion decrease and there is an increase in shear resistance ofthe slope thanks to the roots (Prandini et al.. 1977). On the other hand, the presenceof vegetation may originate negative effects by increasing the load on slopes,enhancing the action of wind forces on the trees and disjointing the soil through theaction of tree roots which widen cracks and favour infiltration (Varnes, 1984).3.3.3 Techniques for landslide investigationsIn order to assess landslide hazard correctly, it is necessary to carry out in-depthinvestigations on the spatial and temporal occurrence of mass movements in the studyarea.The approach to the study of landslides, according to the cases and the scale ofinvestigation, could benefit from various methodologies and techniques, mainly

consisting of field surveys finalized to geomorphological mapping, indirect methodsproducing factor maps depicting areas with different potential landsliding and, lastly,geotechnical and hydrological investigations. When possible, a combination of variousapproaches would be the most suitable answer (Fig. 25).3.3.3.1 Retrospective researchRetrospective research is fundamental in order to define the importance, distributionand repetitivity of slope disarrangements in the territory examined. It can greatlybenefit from historical archive research, since it was demonstrated that manygravitational phenomena (about 90%), even of large dimensions, tend to take placethrough reactivation processes in areas already involved in similar events in the past(Pasuto & Silvano, 1987; Govi, 1988).For this reason archive research is considered as a necessary preliminary step inthe study of the temporal occurrence of landslides. An investigation carried out byBrundsen & Ibsen (1994) showed that most countries in Europe have extensivehistorical sources of great value in assessing the characteristics of geomorphologicalprocesses. These sources mainly consist of narrative in literature, prints, paintings,ground and aerial photographs, remote sensing series, newspapers, maps, scientific73Retrospectiveresearch'- Bibliography- Archives- Radiometric dating- Dendrochronology- Lichenometry-- etc.Data baseand GiS- Storage, treatmentand analysis of data- Link between dataand modelsTECHNIQUESFOR LANDSLIDEINVESTIGATIONSRemotesensing- Ground photographs- Aerial photographs- Satellite and radar imageryMappingDirect mappingIndirect mapping• Land systems mappingGeotechnicalinvestigationsand monitoring- Surface deformations- Subsurface deformations- Groundwater levelFig. 25. Techniques for landslide investigations.

74papers and technical reports. It should be emphasized that it is often difficult to gainaccess to and analyze data from most of the sources mentioned above, because theyare not usually collected for scientific purposes. In addition, the data are generallydiscontinuous in space and time and are influenced by the perception filter of therecorder. Despite these difficulties, archive investigations often allow statisticalanalyses to be carried out.This is the case of the temporal landslide record of the Ventnor complex on theIsle of Wight, off the southern coast of England. The record shows increasinglandslide activity over the present century, partly due to a higher number of eventsrecorded, but also possibly related to increasing rainfall, at least for the recent period(Ibsen & Brundsen, 1996).In general pluviometric series are very significant for the evaluation of thetemporal frequency and distribution of instability phenomena. In fact, as previouslydescribed, meteorological events are often the triggering cause of landslides. On thebasis of the statistico-probabilistic analysis of historical files on climatic data it ispossible to assess the return time of critical precipitations above which widespreadmass movements are started. A frequent recurrence in rainfall time usually implieshigher hazard levels (Govi, 1988).Examples of landslide inventories compiled by government agencies and researchinstitutions are rather numerous nowadays. Nevertheless there have been successfulattempts to set up archives on landslides by single researchers, even in remote times,such as the works by Almagia (1907: 1910) who collected several pieces ofinformation on nearly 800 landslides affecting the Italian Apennines between theyears 1103 and 1908. More recently, in a bibliographical study, Guida et al. (1979)collected references of 950 papers on landslides and hydrological hazards in Italy inthe 1900-1978 period.Landslide inventories, based also on aerial photo-interpretation and field surveysand often resulting in maps, have become frequent since the Seventies in severalcountries (see also Brabb & Harrod, 1989). Among the others, significant examplesrelate to the Czech Republic and Slovakia (Nemcok & Rybaf, 1968; Rybaf, 1973);to some Italian regions (Carrara & Merenda, 1976; Guzzetti & Cardinali, 1989;Antonini et al., 1993) and to the United States (Brabb et al., 1972; Brabb, 1989).Alger & Brabb (1985) carried out thorough bibliographic and archive perusals onlandslides in the United States, collecting over 6,500 pieces of information. Landslideinventories, though representing only a first step toward the definition of landslidehazard assessments or maps are, however, of great benefit from a planning viewpoint.For this reason there is a growing need to create landslide inventories based onthe above mentioned kinds of information and various projects have developed withinthe framework of the International Decade of Natural Disaster Reduction. This iswitnessed, for example, by the activity of the International Geotechnical Societies'UNESCO Working Party on World Landslide Inventory, aiming to contribute to thedefinition of the World distribution of landslides (WPAVLI, 1993). For this purpose,also the AVI project was set up, commissioned by the Italian Ministry of CivilDefence to the National Group for Prevention of Hydrogeological Hazards, aiming

to complete an inventory of the sites historically affected by landslides and floods inItaly and intended to be the first step towards the outlining and mapping ofhydrogeological risk in Italy (Guzzetti et al., 1994). As for the Italian territory, animportant contribution to the definition of landslide hazard and risk was given by theinvestigations carried out within the framework of the SCAI Project (Study onUnstable Inhabited Centres) of the National Group for the Prevention of HydrogeologicalHazards, promoted with the purpose of ranking and representing on mapsthe landslides affecting inhabited centres which had been declared either fit forrestoration or relocation or those in which hazard conditions for public and privatesafety had been recognised. Reviews accompanied by geomorphological maps arealready available for a few regions, such as Veneto (Bozzo et al., 1992), Emilia-Romagna (Annovi & Simoni, 1993), Piemonte (Luino et al., 1993) and Umbria(Felicioni et al., 1994).Retrospective research also has the advantage of landslide dating carried out bymeans of radiometric (usually '"^C), dendrochronological and lichenometric methods,as witnessed also by several authors. As regards the former, which is certainly themost widespread method, dating is carried out on samples of organic material(generally wood and peat) found inside the landslide bodies (Johnson, 1987;Corominas et al., 1994; Panizza et al., 1996b). At present, further perspectives areopening for chronometric investigations related to mass movements occurring in theLate Quaternary, thanks to the development of analytical techniques, such asAccelerator Mass Spectrometry (AMS), Thermally Ionized Mass Spectrometry(TIMS) and laser fusion, and new dating methods, such as Optically StimulatedLuminescence (OSL) dating and alpha recoil dating (R. Dikau, pers. commun., 1995).A significant advantage lies in the possibility of dating events directly; for example,the age of aspect of a landslide scarp can be obtained by determining cosmogenicnuclides produced in situ (see Nishiizumi et al., 1993). In addition, these methodsenable the dating of materials other than organic ones. For example, OSL methodmay be used for debris flow, mud flow or rock avalanche dating, on the basis of theexposure of mineral grains to daylight.3.3.3.2 Databases and GISAn important aspect of landslide investigations is the possibility to store, treat andanalyse the spatial and temporal data available. With respect to the application of datacapturing technologies, such as remote sensing, radar and Digital Terrain Models,computer tools are fundamental in guaranteeing the necessary links between data andmodels. In fact, temporal data can be used to define the occurrence of landsliding interms of time series analysis or to evaluate spatial landslide patterns in terms ofregional hazard assessments. These assessments consist of probability statements andlandslide hazard scenarios concerning future slope stability (Dikau et al., 1996).A database generally stores attributes given to individual landslides in previousinvestigations. These attributes include a wide range of lithological, topographic,geomorphological and geothechnical information. There exist several code tables andchecklists for the collection of data to be stored in databases (Carrara & Merenda,75

761976; Pasek, 1975; Pasek et al., 1977; Kienholz, 1984: WPAVLI, 1990, 1991; Chaconet al, 1992). A significant example of a landslide database is that of the UK NationalLandslide Data Base, produced by Geomorphological Services Limited (GSL) for theDepartment of the Environment between 1986 and 1989, which results from a fullycomprehensive study of literature and maps concerning landslides, though it is stillnot representative of the total distribution of mass movements in the UK. For eachlandslide record the database includes several attributes, which are displayed in theNational Landslide Databank codes table (bedrock and superficial geology, type, age,etc.; see Ibsen & Brundsen, 1996). When the data on a landslide are complete, thisdatabase provides very useful information ranging from the geological aspects to thetechniques used to investigate a landslide. Time attributes are a weak point of thisdatabase, since subdivision according to age is very limited; in fact these temporalaspects are unfortunately not always included in databases.Research carried out within a European Programme on Climatology and naturalHazards (EPOCH) dealing with the temporal occurrence of landsliding in theEuropean Union (Casale et al., 1994) has provided data for the improvement, in termsof time attributes, of landslide databases of selected sites. Dendrochronology datingshave been obtained for the Spanish Pyrenees (Corominas et al., 1994) and radiometricdatings have been made in the area of Cortina d'Ampezzo (Dolomites, Italy)(Gasparetto et al., 1994; Panizza et al., 1996a). Furthermore historical archive datahave been gathered for Germany, France and the southern coast of Britain. TheEPOCH Project above mentioned has also contributed to the definition of temporalattributes of landslides in terms of activity, defining the type, the return period, themode and the period of latest activity, besides the state of activity generally foreseenin databases (Flageollet, 1996; see Fig. 26).Geographical Information Systems (GIS) contribute to landslide research bystoring, handling and analysing spatial and temporal data. These operations mainlyaim to draw up landslide susceptibility and hazard maps, displaying the potentiallocation and intensity of future mass movements, and to analyse landslide time seriesin relation to triggering factors. Geological maps, slope morphometry and landslideinventory maps make up the most important databases for these GIS analyses (Fig.27). Through landslide susceptibility maps, which are quite easy to read fornonspecialists, decision-makers may be provided with a cost-effective policy optionfor coping with landslides. Examples of landslide susceptibility maps are provided byVarnes (1984) and Brabb (1984; 1993; 1995).However, Dikau et al. (1996) stress that though databases and GIS are potentiallyvery powerful, they are just technical tools ''which cannot replace the necessity toimprove our understand of the landslide process itself in space and time" and cannotobviate fieldwork.3.3.3.3 Remote sensingRemote sensing is a very powerful tool for the study of landslides and the assessmentof landslide hazard, especially because it is generally cost-effective and allowsmultitemporal reconstruction to be carried out. Remote sensing data can be used at

77STATE OFACTIVITYTYPE OFACTIVITYRETURNPERIODPERIOD OF LASTACTIVITYMODE OFACTIVITYINACTIVESTABILISEDdefinitely orlong termlong term(> 1.000 yr)Prequaternary(> 2.000,000 yr BP)RANDOMDORMANT —^temporarily or in apredefined period(i.e. 200 yr)ACTIVESINGULAR(one event on record)EPISODIC —>renewal failure(irregular evolution)I— INTERMITTENT- nonseasonal- seasonalreactivation failure(regular evolution)I-CONTINUOUSI— low frequency(100-1,000 yr)medium frequency(0-100yr)high frequency(1-10 yr)- very highfrequency(

78thanks to their wide geographical extent, while vertical stereoscopic aerial photographsare fundamental for landslide investigations ranging from a regional to a localscale (Hansen, 1984; Brundsen, 1993; Hutchinson, 1995). In both cases multitemporalcovers are often available.Satellite imagery has been used in landslide studies since the midseventies, butmainly for scientific purposes; this is due to poor definition, which generally enablesthe user to detect only large mass movements, and to the lack of stereoscopic cover.According to Brundsen (1993): 'it is certain that there are satellites capable ofrecording the detail required but the results are not open to current work" becausepriority is given to security. However, the availability of satellite imagery with spatialresolution below 10 m and with stereo capabilities is expected in the next decade(Mantovani et al., 1996). Nevertheless several authors have used LANDS AT or SPOTimages for the identification of mass movements, which are recognised indirectlythrough specific terrain conditions associated with landslides, such as changes inlithology, vegetation and soil humidity, and not through morphological evidence asis the general procedure with aerial photographs (Rib & Liang, 1978). In practice, forthe inventory mapping of landslides and the assessment of slope instability, satelliteimagery and large-scale aerial photography are used in combination, the latter for thestudy of representative sample areas and the former for extrapolation of the findingsto wider areas (Mantovani et al., 1996).Infrared imagery provides valuable information for the identification of theexisting landslides and of landslide-susceptible terrains. In fact, according to Rib &Liang (1978), they provide information on surface and near-surface moisture anddrainage conditions as well as indicating the presence of bedrock at shallow depthsenabling a distinction between loose superficial deposits and bedrock.Other remote sensing techniques, such as multispectral imagery and microwaveradiometry, may be used in landslide investigation, but they have been applied in alimited number of cases. However, there are significant perspectives in advancedremote sensing techniques which may also give input data for CIS systemsparticularly regarding soil moisture and subsurface water concentrations (Brundsen,1993). Systems such as AIRSAR (Airborne synthetic aperture radar) or AVARIS(Advanced airborne visible/infrared imaging spectrometer) can be very valuable forthe study of shallow landslides and forested slopes. Within the coming decade therewill be increasing availability of radar satellite imagery (ERS-1, ERS-2, JERS-1,Almaz, Radarsat), which, however, because of geometric distortion will give ratherpoor quality images in mountainous regions (Mantovani et al., 1996).Remote sensing techniques are, however, traditionally based on the use of verticalaerial photographs on various scales (generally ranging from 1:5,000 to 1:70,000)which can be monochrome, true colour, false colour and infrared. Aerial photographsare generally more easily available with respect to the above described images andshow higher definition. The greatest advantages of using aerial photographs inlandsHde studies are the following (Rib & Liang, 1978):— the use of aerial photographs gives a three-dimensional and overall view of arelatively large area;

— the boundaries and morphological features of existing mass movements can beidentified;— hints of incipient movements (scarps, cracks, etc.) can be observed over a widearea;— surface and subsurface drainage patterns can be outlined:— relationships between topography, drainage patterns and natural and man-madefeatures often become evident;— rock formations and superficial deposits can be observed in their undisturbedconditions;— geomorphological features can be identified even if a vegetation cover is present,which makes observation quite difficult during fieldwork;— continuity and recurrence of geological and geomorphological features can bedefined; and— the temporal occurrence and development of landslides can be outlined bycomparing photographs of different periods.With respect to the possibility of reconstructing slope evolution, interestingperspectives come from the application of analytical archive photogrammetry, which"represents a development of conventional photogrammetry made possible usingcomputerized analytical methods" (Chandler & Brundsen, 1995). This techniqueenables precise spatial data to be obtained from a wide variety of historical andarchive photographs, including oblique photographs. Two images of the same objectand at the same time are needed even if taken from different positions and withdifferent cameras. With this method, which involves the use of a graphics laboratory,it is possible to produce data location maps, contour maps, profiles, DTM's and otheranalytical illustrations. This technique has been developed and tested in the study ofthe Black Ven landslide in Dorset (England) using oblique and vertical aerialphotographs taken at five intervals from 1946 to 1988 (Chandler & Brundsen, 1995).3.3.3.4 MappingMapping is often a necessary step in landslide hazard studies. Maps may consisteither of basic documents such as geomorphological maps and landslide maps or oflandslide susceptibility maps and hazard zonation maps. Mapping can be defined asdirect, when the landslide extent and distribution are recognised on a geomorphologicalbasis with the aim of extrapolating slope stability assessments to the rest ofthe investigated area, or indirect, when the possibility of landslide occurrence isassessed in relation to the controlling factors, with or without consideration oflandsUde distribution (Hansen, 1984).Direct mapping is usually obtained through aerial photo-interpretation and groundsurveys, which vary proportionally according to the scale adopted for the study,together with bibliographical and archive investigations. The result can be inventorymaps (see also section 3.1) which record landslide distribution over an area (Nemcok& Rybaf, 1968; Brabb et al., 1972; Rybaf, 1973; Carrara & Merenda, 1976;Radbruch-Hall et al., 1976; Conway et al., 1980; Alger & Brabb, 1985; Guzzetti &Cardinali, 1989; Antonini et al., 1993). They are generally the basis for further79

80detailed studies aiming to assess future failures. The information contained in thesemaps may also include landslide type, bedrock lithology, superficial deposits, slopeangles, engineering geological zonation, etc.Geomorphological maps are another product of direct mapping. These aregenerally at a larger scale (less than 1:25,000) than those described above and forma very useful basis for landslide hazard studies since they include details on generalslope morphology and related processes, and define the type of failure and degree ofactivity as well as the features associated with landslides (for a review of geomorphologicalmapping methods and legends see Tricart, 1965; Bashenina et al., 1968;Verstappen & Van Zuidam, 1968; Demek, 1972; Panizza, 1972; Demek & Embleton,1978; Barsch & Liedtke, 1985; de Graaf et al., 1987; Cooke & Doomkamp, 1990;Pellegrini et al., 1993; Gruppo di Lavoro per la Cartografia Geomorfologica, 1994).Geomorphological mapping may be easily and usefully applied to the study of massmovements. There exist many significant examples of landslide-orientated geomorphologicalmaps, such as that of Brundsen et al. (1975), carried out with aim ofidentifying landslide hazard in an area of Nepal where the construction of a road anda bridge was proposed, or that of Panizza (1990) where the landslides surroundingthe town of Cortina d'Ampezzo (Italian Dolomites) are mapped in detail. Aninteresting attempt to include the temporal aspect in landslide mapping was made byFlageollet (1994) in the above mentioned Dolomite area on the basis of data andmaps collected and elaborated by Panizza (1990) and Gasparetto et al. (1994). Thetemporal information reported on the computer-based landslide map of the area ofCortina d'Ampezzo is related to periods of activity during the Holocene and to thefrequency and incidence (first time failure or removement failure) of the movements.Geomorphological maps may in many cases be too complicated to be read bynonspecialists. This is the reason why planners and engineers are generally providedwith derivative maps which appear simpler from a purely graphic standpoint and takeinto account only those processes and landforms that are connected with slopeinstability. The product can be a geomorphologically-based landslide hazard map.Many examples, carried out according to different methodologies, are known inliterature. The first example should refer to the French ZERMOS (Zones Exposeesaux Risques de Mouvement du Sol et du Sous-sol) hazard maps which have beenproduced for several sample areas at a scale 1:25,000. The hazard (actual andpotential) is assessed and rated taking into account distribution of landslides,evidence of instability, as well as geological, geomorphological and hydrologicalaspects (for further details on methodology and limits, see Antoine, 1977; Humbert,1977).Another significant example is provided by Kienholz (1978) who carried out astudy in the Grindenwald, an area of the Swiss Alps affected by mass movements andavalanches; first a geomorphological map was produced and from this a naturalhazard map was obtained. The degree of hazard was assessed for a high number ofpreviously defined geomorphological units using checklists.When the casual factors of landslides can be recognised, measured and mappedand the analysis of the distributions of the different factors controlling landsliding can

e made, indirect mapping can be carried out.An original method aiming at the elaboration of hazard susceptibility maps hasbeen defined and tested in a few sites in Italy (e.g., Panizza et al., 1980; Carrara etal., 1987) and has been recently adopted by the National Geological Survey as theofficial procedure for the compilation of geological hazard maps (Amanti et al.,1992). This method includes both indirect and direct mapping procedures. In fact, thisapproach consists, on the one hand, of the analysis of the causes of instability(ascribable to both slope and fluvial processes) which are outlined in a series ofthematic maps (geological, hydrogeological, vegetational, etc.) and weighted bymeans of specific procedures, with the aim of producing a first derivative map(integrated analysis map) depicting the distribution of potentially unstable areas. Onthe other hand, by means of geomorphological investigations, the analysis of theeffects of instability is carried out in order to give an outline of landforms andprocesses, both active and inactive, referable to geomorphological instability. Thecartographic documents produced during this phase are a geomorphological map anda second derivative map (map of geomorphological dynamics) showing the areaswhich are at present unstable. The comparison and critical discussion of these twoderivative maps lead to the production of a "geomorphological hazard map", aconcise document depicting present and potential unstable areas subdivided accordingto the causes of instability (see also chapter 3.9).A partly similar approach was used for research on landslide hazard in Tuscany(Italy) which led to the elaboration of several landslide maps, accompanied bygeological information permitting the assessment, albeit qualitatively, of the ratiobetween the degree of stability attributed to an area and its structural characteristics.In these hazard maps the following categories are distinguished: highly hazardousareas, including active and dormant landslides, areas characterised by high potentialinstabiUty linked to the morphological aspects, areas prone to landsliding owing tolithological aspects, areas of medium stability and finally stable areas (Nardi et al.,1985, 1987; Dalian et al., 1991).Jones (1992) refers to a further approach. Land Systems Mapping, which is placedamong indirect mapping techniques and is based on the subdivision of the studyterritory into limited areas (land systems, land units, land elements, passing fromlarge scale to small scale subdivisions) in which predictable combinations oflandforms, soils, vegetation and superficial processes take place. This approach,created with the goal of producing basic maps for rural planning (Christian &Stewart, 1952), has been extremely useful in landslide hazard assessment since itallows large portions of territory to be quickly classified providing a useful regionalpicture for data collection and storage (Savigear, 1965; Wilhusen, 1979; Styles et al.,1984; Kienholz, 1984; Cooke & Doomkamp, 1990).3.3.3.5 Geotechnical investigations and monitoringSlope movements show great variety not only because of the different types but alsofrom a kinematic and geometric point of view. Each landslide is characterised by itsown evolutive story which necessarily conditions the types of instruments to be81

82installed, the number and location of measurement points, the frequency of sampling,etc. Standardisation of the methods of intervention and the choice of sensors to beused is therefore a difficult task to be achieved. The scheme of instrumentationshould be based on in-depth geological and morphological information of the site aswell as on an accurate back analysis of all historical and bibliographical dataavailable.In order to obtain relevant results, a monitoring system should not only be theresult of the sum of various technologies but above all of a preliminary analysis ofthe phenomena and should derive from adequate reflections on the data. Similarly,a set of sensors placed haphazardly inside and around a landslide body will producea series of measurements which are not easy to interpret and compare (Angeli et al.,1994). Therefore it is important to plan a monitoring system correcdy, in order to getsufficient and, in particular, reliable data when the alarm for the population, the riskdefinition, slope modelling and stabilisation can be predicted.Methodological aspectsThe use of slope instrumentations and the planning and installation of more complexmonitoring systems are necessary when the various problems concerning slopestability have to be faced. Moreover, these instruments produce a considerableamount of data which can be particularly useful in slope stability analysis andmodelling with results that will mostly depend on the input data quality.Four different stages can be identified (Sowers & Royster, 1978):1) Bibliographical analysis concerning the geological and geomorphological aspectsin order to acquire a general view of the problem.2) Boring, sampling, testing, etc., in order to better characterise the phenomenonstudied from a geotechnical, hydraulic and kinematic standpoint.3) On the basis of the data previously collected the areas which require furtherinvestigations are pointed out, thus returning to the second phase.4) The last stage consists in the installation of a monitoring system, the assessmentof its reliability and a constant control of the areas most exposed to risk.Monitoring can be used for different goals: on the one hand for investigationsfinalised to possible upgrading interventions on a slope affected by mass movementsand, on the other hand, for safety and control works and for testing the effectivenessof certain operations aiming at increasing the level of civil defence in the event oflandslides threatening inhabited centres.One should always bear in mind that: "...instrumentation is merely a tool, ratherthan an end in itself..." (Dunnicliff, 1995) and that installation should always bepreceded by a careful analysis of the situation which will allow some hypotheses tobe formulated on mass movement evolution. In this way, it will be possible to decidethe kind of measurements to be carried out, which instruments to be used and the bestplanning for positioning sensors as well as choosing an appropriate number, the depthof installation and adequate recording systems (Wilson & Mikkelsen, 1978).The main goals concerning the use of instrumentation and monitoring systems arethe following:

— to determine the geometry and depth of the shp surface;— to measure both vertical and horizontal movements of the unstable rock mass;— to assess the rate of movements (acceleration or deceleration);— to record the changes of the water table, possibly with respect to the climatictrend of the area (mainly precipitations);— to provide an adequate alarm system in case of impending danger for publicsafety; and— to verify the effectiveness of the control measures.Naturally all these functions can be carried out in the presence of a slope movementwhich has already developed in its main aspects or as a precautionary measure whenit is necessary to plan some engineering works or urban development which couldinduce conditions of instability in the surrounding territory.Sensors and instrumentationFrom the remarks previously made, it is evident that there are two main parameterswhich should always be known when studying, surveying and measuring a massmovement. These are: deformations, both superficial and deep, and groundwaterpressure. Since these magnitudes are directly correlated to meteorological factors,on which also the functions of some sensors depend, such as rainfall, temperature,barometric pressure, etc., it is opportune to survey and record also these parameters.The characteristics of the main and most frequently used instruments suitable formonitoring the above illustrated parameters, will now be discussed; although it is notthe aim of this chapter to provide with an exhaustive review of all types ofinstruments used for landslide monitoring which are better illustrated in more specifictexts and articles (e.g., DunnicHff, 1988).Monitoring of surface deformationsSuperficial slope movements are normally monitored in order to determine thechanges in superficial morphology of the landslide area, the spatial extension of thedeformations and, if possible, the tendency to retrogression or enlargement and,finally, the size of the movements.Quick, generally very economical methods are used in emergency situations andwhen the amount of movements is considerable. They consist of metre tapes or rodsplaced across the most active cracks or, if the movement affects a rock mass, in glasstelltales cemented across each crack. These simple instruments can provide usefulinformation on the movement's mechanism and direction.More precise measurements can be obtained by means of strain-gauges which canbe made of threads, rods or tapes (the former being used also for surveyingdisplacements at depth). This kind of apparatus is usually fitted out with electrictransducers which transform the measurements provided by the instruments intoproportional electric impulses which can be continuously recorded.Tiltmeters measure instead the rotational component of a point's displacement.Topographic precision instruments can survey displacements of points consideredin movement with respect to fixed ones with a precision which depends on the83

84distance between the instrument and the surveyed point and which is usually around15 mm.Also precision levels can be utilised; they are generally suitable for monitoringsettlements at the crest of the slope or along the intermediate benches on the slopeface (Kobold, 1961).For the control of horizontal movements a precision theodolite equipped with aninfrared diastimeter is generally used. In this case, a system of local bench marksshould be set out, both inside and outside the landslide body whose position isperiodically checked from positions considered fixed. This method offers veryaccurate precision and measurements can be carried out even over long distances,although temperature and barometric pressure should always be taken into accountsince they could induce errors in the values read by the diastimeter.An important contribution to the measurement of superficial displacements isnowadays offered by the GPS (Global Positioning System), which is based on the useof 18 satellites, positioned along different circular orbits at about a height of 20.2 km,and one or two receiving stations on the Earth's surface. In this way, both relativepositions of two points (up to distances of about 1 km the precision is 5 mm) andabsolute altitude measurements (in this case the errors are around 10 cm) areobtainable. The development of this system has undergone considerable delay owingto the interruption of the US Space Program which had planned sending into orbitseveral other satellites which could be used for this purpose. As a consequence, atpresent use is limited to some specific times of the day. Also the relatively high costsand difficulties in the data elaboration have reduced its potential.Another method applied is terrestrial photogrammetry, especially for themonitoring of excavation fronts, rock movements or whenever the direct access to theslope is not possible. This method is based on the use of a phototheodolite whichallows successive stereophotographs to be taken from a fixed station; these picturescan be compared in order to evaluate the displacements of fixed targets or to indicatemovements wherever these might develop.From the stereoscopic model it is possible to obtain a Digital Terrain Model bymeans of sophisticated calculation programmes, thus enabling the operator to getquantitative evaluations. The accuracy of this method is not very high and isproportional to the distance between the phototheodolite and the slope; precisionmeasures around 20-30 mm over distances of about 100 m can be achieved.Monitoring of subsurface deformationsMeasurements of displacements in the subsoil are of paramount importance foridentifying the depth of a slip surface and assessing the volume of the rock massinvolved in the movement, the presence of one or more deformational horizons andthe amount of their movements. The methods for monitoring displacements in depthrequire the use of instruments which should be positioned inside boreholes, whoselocation and depth should be decided on the basis of accurate preliminary investigations.The instruments most frequently used for these measurements are the following.

The inclinometer is generally used for evaluating the depth of the failure surface(Angeli et al., 1989) and the movements along this surface; it measures the changesof inclination in a tube in two mutually perpendicular near vertical planes. Thereadings are performed at prefixed depths inside the tube and allow the change inslope at various points to be determined. The instrument records the temporaldeformation trends of the tube and provides information on the amount and directionof the movement and on the depth of the slip surface.Borehole extensometers work in the same way as those utilised for superficialmovements. In this case, though, the wire should be adequately protected by asheathing from direct contact with the soil and anchored well beneath the failuresurface at the bottom of piezometric or inclinometric tubes. These devices can beused to monitor movements perpendicular to the axes of the boreholes inside whichthe instruments have been installed. Precision is not less than 1 mm. Inside the sameborehole it is possible to install several wires anchored at different depths in orderto identify also the position of the movement surface.Monitoring of acoustic emissions generated within the rock mass can give usefulinformation on the degree of activity of the mass movement and, if correctly placed,also on the depth of the failure surface. This method is still being tested but it willprobably give positive results. Sensors are used such as geophones which transformthe elastic wave propagating through the ground (determined by the acousticemission) into an electric signal proportional to the emission amplitude. The systemis most effective when the amplitude of the signals is high, that is for rocks andcohesionless soils rather than for cohesive soils.Monitoring of groundwater pressureGroundwater level plays a very important role in slope stability and therefore themonitoring of this magnitude is extremely useful, especially if related to meteoricinputs and displacements. When a landslide occurs, porewater pressure should bemeasured in proximity to the slip surface, thus enabling effective stress analysis tobe performed. Groundwater pressure is generally monitored by means of openstandpipes, vibrating wires, pneumatic or electric piezometers.Monitoring of climate (weather)The monitoring of meteorological parameters in the study area is very importantconsidering the influence that they exert on the evolutive dynamics of slopemovements. Correlations of these magnitudes with hydrogeological and kinematicones gives a better understanding of landslide mechanisms and can also produceuseful forecasting elements, especially in the case of an automatic warning and alarmsystem.The parameters most frequently surveyed are:— rainfall and snow-water equivalent, measured by means of a tipping bucket raingauge,which can be provided with a warmed collection funnel in order tomeasure the water-equivalent of snowfall;— temperature;85

86— snow depth, measured by ultrasonic snow gauge; and— barometric pressure.In addition, also wind intensity and direction can be surveyed, as well as sunirradiation and air humidity. All these sensors are usually connected to a data loggerfor automatic acquisition.3.3.4 Landslide hazard assessmentIn the previous chapters a definition of landslide hazard was given. It refers to thepossibility that a landslide of a certain magnitude takes place in a particular timeinterval and in a specific area.This definition shows that there are two precise domains in which landslidehazard can be assessed: the temporal and spatial domains. Therefore, an evaluationof landslide hazard should answer two main questions (Hartlen & Viberg, 1988):1) Where will the landslide(s) occur?2) When will the landslide(s) occur?The spatial aspect defines the areas where instability processes are more likely todevelop in a certain length of time, the temporal one should in some way lead to aforecast of the moment when instability phenomena could occur in a certain area.At this point it is opportune to emphasize the difference between landslideforecasting and landslide prediction since, according to Jones (1992): "the former isfocused on identifying the location, magnitude and timing of specific events, normallybased on monitoring procedures, so that emergency actions may be achievedefficiently whereas the latter is spatially extensive and concerned with establishingzones of different level of threat by emphasizing the magnitude-frequency characteristicsof recorded landsliding and probability of slope instability" (see also Flageollet,1989).The spatial aspect can in turn be considered from two different points of viewwhich necessarily imply the application of diverse investigation methodologies. Onthe one hand there is the hazard originating in a single slope movement or in alimited portion of slope; in this case the investigations will tend to concentrate on aspecific site and to assess in particular the subsoil's characteristics (Hutchinson,1995).On the other hand there is the assessment of landslide hazard on a regional scalewhich, owing to the different methods of investigation utilised, will give moreimportance to the aspects concerning the superficial morphological characteristics ofthe area examined, without studying the subsoil's characteristics in depth, or doingso only in specific points.Several authors have proposed diverse methodological approaches in order todefine landslide hazard. Usually the main goal is to produce maps able to classify allexisting landslides and to zonate also the areas at present stable by rating them withdifferent degrees of hazard susceptibility, assessed on the basis of geological,geomorphological, morphometric and geotechnical aspects, independently of theinvestigation scale (Meijerink, 1988).

In a broad sense, the techniques apphed can be subdivided into quahtativeevaluation (relative mapping) and quantitative assessment (absolute methods)techniques.As for qualitative hazard evaluation, several Authors have proposed differentinvestigation methodologies. Some of them concern mapping methods, like thoseused, for example, in the ZERMOS project in France, by Kienholz (1978) in theGrindelwald area in Switzerland or by Seijmonsbergen (1992) in the Vorarlbergregion in the Western Austrian Alps. These approaches are mostly based on the useof direct survey in the field and the drawing up of several mapping products whichshould be compared in order to come to a qualitative evaluation of landslide hazard.Moreover, other qualitative approaches based on the application of statisticalmethods have been proposed. According to these, the area to be analysed should besubdivided into grid cells and would require as input data a landslide distribution mapand a land-unit map. A second stage envisages the identification of the mostsignificant slope stability controlling parameters which are afterwards stored as codedterrain attributes (e.g., geology, morphometry, hydrology, etc.) in a database. Thestatistical elaboration of all these data for each of the grid cells identified will leadto the definition of the areas affected by different landslide susceptibility. Forexample, Carrara & Merenda (1976) used grid cells of 200 x 200 m in an area of 600km^ obtaining a slope stability hazard map from the statistical analysis of more than30 attributes.The recent application of GIS methods was shown to be particularly fruitful inassessing landslide hazard, especially since it is possible to undertake the study ondifferent scales, from regional to site investigation scale; each scale requiring its owninput maps and mapping unit attributes. If the regional scale is chosen, the dataconcerning the geological and geomorphological features are put together with otherparameters linked to slope stability. For each of the above listed parameters, therelative contribution to slope failure is estimated, thus a zonation of the study areain terms of landslide susceptibility can be carried out. Statistical treatments, such asmultiple regression or discriminant analysis, have been recently incorporated in GISrecording systems (Carrara et al., 1991) and ''favourability functions" have beenderived (Chung & Fabbri, 1993). However, these methods are dependent on the scaleof the discretisation of the slope system and do not generally take into account thefailure mechanism so they do not always completely explain the slope failuredistribution.As regards landslide hazard assessment on a detailed site investigation scale,absolute or numerical methods are more and more utilised. Such methods, based ondeterministic approach, express landslide hazard, through stability modelling, in termsof safety factor or of probability that a certain event might take place. The requiredinput data are: depth of the failure surface, soil strength parameters, slope angle andporewater pressure. It is possible to combine the use of GIS with these deterministicmodels following diverse approaches, among which the use of an infinite slopemodel, which calculates the safety factor for each pixel or the selection of a numberof slope profiles or pixels from the GIS which are subsequently exported to external87

88slope stability models (Van Westen, 1994).An improvement of the climatic input data for the deterministic models wasobtained through the development of general circulation models (GCM's) which havebeen recently used to deduce regional-scale climatic features. Downscaling of GCM'sis made by means of a statistical treatment which interrelates the characteristicpatterns of regional climate parameters and large-scale atmospheric flow (Von Storchet al., 1993). Rainfall occurrence obtained through this procedure can be used as inputdata for hydrological and slope stability models.It must, however, be emphasized that the quality of the results of GIS analysisand modelling is always strictly connected with the precision and number of inputdata for each parameter considered; therefore even if extremely powerful technologiesand computer-based media are available, the reliability of landslide hazardassessment depends very much on the experience and ability of the scientists andtechnicians involved in archive analysis, remote sensing, ground survey, mapping andmonitoring.It is particularly important that landslide specialists provide planners and decisionmakerswith valuable and reliable landslide hazard assessments; this may help theincorporation of these assessments in land planning policies, which have beenquite limited so far. This could give a further contribution to invert the widespreadtendency of many countries to face the landslide problem only in terms ofpostevent clearance and remedial measures instead of adequate prevention planningpoHcies.3.4 River hazard3.4.1 River erosionSometimes with the term river erosion extremely different morphogenetic processeslinked to the action of a watercourse are defined; this can lead to some confusion indescribing phenomena which differ in their origin and evolution. It is therefore offundamental importance to distinguish the following types:— erosion in the strict sense;— cavitation;— abrasion;— degradation.With the term river erosion in a strict sense the removal and loading of detritalmaterial from a riverbed bottom and banks is intended.With the term river cavitation the mechanical action of water only on riverbedsides and bottom is intended.With the term river abrasion the mechanical action following the impact ofdetrital materials transported by the river current is intended.With the term river degradation the whole complex of morphological phenomenalinked to the presence of a watercourse is intended. For example, the fragmentation

of the riverbed rocks owing to physical or chemical processes, such as gelivation orhydrolysis, determined by the river's water; or mass movements occurring on theriver banks following the undermining of the slope's toe, etc.3.4.1.1 Erosion in the strict senseIn order to have material load transport, the current's kinetic energy must exceed theforces of gravity, inertia, friction and cohesion which tend to keep detrital particlesin a motionless state.Erosional processes in a strict sense and those derived from transport anddeposition are a function of several variables: on the one hand the current's velocity,density, turbulence, load, etc.; on the other hand the detritus's dimensions, bulk unitweight, shape, etc.The ratio between the current's velocity and the dimensions of individualparticles is represented in Sundborg's diagram (Fig. 28): in abscissa the particles'diameters are shown whilst in ordinate the current's velocity pattern is represented.It is seen that for each detrital element there is a critical velocity above which theelement is removed and loaded, i.e., eroded; similarly there is a critical velocitybelow which the element can no longer be kept in motion, i.e., transported and,therefore, it is deposited. This shows that the velocity necessary for removing aparticle from the riverbed bottom seems to be greater than that necessary formaintaining its transport. Moreover it can be observed that the dimensions of thematerial transported in suspension increase with velocity, to the detriment of thosetransported at the bottom.89400cm/s2001001 • 1 1erosion s.s.61 _60402010+SU2 upended lo»ad^"* "* X.vo^i{BiSf^'v^eVb\depositionI I Ibed loads^Js sCM Tf CO "«-CO '^ CM Tt CO£O O O Od d dP P P d o oEo o oclay silt sand gravelFig. 28. Sundborg diagram (1967).CO O O

903.4.1.2 CavitationMechanical actions of this kind are due to tiny bubbles of water vapour formed bysharp variations in hydric pressure. Sudden velocity increases and turbulentmovements can determine a pressure decrease along the sides of the riverbed, withconsequent water vapourisation. These bubbles behave as detrital elements and theirconstant formation and destruction gives rise to an extremely rapid sequence ofimpacts on the sides with consequent disgregation of the rocky material. A similareffect is created by the violent impact of water at the foot of a waterfall.The mechanical effects of cavitation do not seem to be very important in thegeneral frame of river erosion.3.4.1.3 AbrasionThe mechanical processes linked to detrital particles carried by the watercoursedepend on the quantity and size of the latter. The action of clayey and silty materialsis neghgible. Sands mainly produce a smoothing action on rocky riverbeds whichleads to progressive wearing but, nevertheless, is unfavourable to the variousphenomena of geomorphological erosion since polished rocks are more resistant thanthose with discontinuous, rough and irregular surfaces. Coarser materials collideindividually with the riverbed walls causing disjointedness, divarication anddisgregation which are a function both of the current's impact energy and of theriverbed rocks' cohesion.3.4.1.4 DegradationThe presence of the watercourse determines a set of degradation phenomena alongboth the river banks and the slopes overhanging the watercourse.During minimum-flow periods, the riverbeds are subject to weathering andphysicochemical alteration processes linked both to climate and lithology: in colderregions a rocky bed can undergo gelivation processes whilst in humid regionshydrolysis, solution, etc., prevail. The alternations of emersion and submersion fromthe water can cause the breaking up of rocks subjected to repeated cycles of wettingand desiccation. These and other processes can reduce the rock resistance to riverabrasion and cavitation or lead to a real fragmentation with consequent productionof detritus which is afterwards rearranged and removed by the current in the form oferosion in a strict sense.River-bank erosion processes (in a wide sense) can accelerate and provoke slopedegradational phenomena, such as mass movements or, in any case, inducedisequilibrium conditions.River processes taking place within a given time, including maximum andminimum flow phases, can be summarised in the following way. At the beginning ofthe highwater period, the river-bottom detrital materials are subject to rearrangementand erosion in a strict sense; afterwards, with the progressive increase of watervolume and particle load the velocity at the bottom of the river decreases. Thus,bottom erosion in a strict sense stops while abrasion and disarrangement can occuralong the banks, with consequent bank erosion and possible slope degradational

phenomena. On the contrary, the decrease of a major flow causes sedimentation ofmaterials along all the inundated bed. Finally, when the flow goes back to normallevels and is no longer loaded with debris, bottom erosion in a strict sense resumes,affecting the newly deposited material. This kind of erosion continues also during theminimum-flow period. After all, the balance of a maximum-flow event is sedimentation,possibly accompanied by river bank erosion and slope degradationalphenomena; on the contrary, the balance of a minimum-flow period is a cutting intofreshly deposited alluvial sediments.3.4.1.5 The action of mountain streamsA particular reference must be made to the degradational processes caused bymountain streams which, among the various types of watercourses, are particularlyenergy-rich geomorphological agents.The main characteristics from which their geomorphological effectiveness isderived are the following (Tricart, 1977):— they show riverbeds with a usually high slope angle;— they show a various and irregular course, with frequent changes of slope angleand variations of riverbed width;— they flow on extremely heterogeneous material, ranging from more or lesscohesive bedrock to load-assumed detritus and large boulders fallen from thesurrounding slopes.They are moreover characterised by very irregular regimes, more or less accentuatedaccording to the climate peculiarities: major highwaters which noticeably modify thewatercourse's morphological features and sometimes also those of the surroundingterritory; generally extreme minimum flows which, on the contrary, exert no influencewhatsoever on the riverbed.During major highwaters, caused by sudden and violent storms, waters convey ahigh load of debris such as mud, stony fragments and vegetal remnants, thusmaking up a high density and velocity mass, therefore characterised by noticeableenergy. Slope angle and width changes determine frequent and successive episodesof sedimentation and transport of other material, with load substitution processes.Overflows from the ordinary stream bed and bank erosion actions take place, withconsequent undermining of the slope toes, degradation and eventually triggeringof mass movements. Downstream, at the end of the course, the load of themountain stream is unevenly spread at the base of the relief, owing to the twofoldeffect of slope angle and spreading decrease and loss of water which is nolonger confined between the narrow flanks of the mountain valley. In this wayproluvial fans are formed which are a transitional form between slope and alluvialfans.The dynamics of these processes, intermediate between river and slope processes,can cause hazardous erosion and inundation effects, with even disastrous consequencesfor buildings, farming activities and sometimes human lives.91

923.4.2 River instability'^*by Franca MARAGA'3.4.2.1 General overviewThe dynamic action of waters moving in a stream channel and materials carried bythem can produce important changes in the environment: they interfere with aterritory's socioeconomic development, where land reclamation for productionactivities or urban settlements has directly influenced the fluvial system. Suchchanges can create geomorphological hazard situations under the variable impulse offloods both in mountainous regions and in the plain, with morphogenetic processescharacterised by different dimensions and lengths of time.The processes are sometimes occasional, often repetitive and in any caseinterdependent on the effects produced along the watercourse in spatial and temporalsuccession, with long-term consequences for the whole hydrographic network. Theextreme diversity of the processes makes a river hazard difficult to assess usingprediction criteria, since this would be defined by local, natural and man-induced factorsin periodical adjustment, so as that give rise to conditions of hydrodynamic equilibriumduring the propagation of a flood wave. Even in short periods of time, theevolution of the composite physical fluvial system, defined by the channel and by itsflood plain, can be identified as a "dynamic metastable" (Schumm, 1977) compositesystem of equilibrium, with a recurrent step of evolution during overflow events.The velocity of hydrodynamic parameters conditions the intensity of the activatedprocess and therefore the "pressure" of the consequent effects on the territory for thesame length of time. An area subject to flooding, for example, faces a higher hazardif the flood rises suddenly with a high overbank flow speed.The hazard of watercourses is mainly connected with occasional and exceptionalchanges of their water stages occurring during extra-bank flow rather than with thechanges periodically generated by ordinary flow, the latter being more frequent butless noticeable. The channel can be considered a fluvial form constantly adjustingitself to changes occurring at times along its course in the short and long term, whilstthe alluvial plain behaves as a form in occasional adjustment, over long periods oftime.Usually the river hazard is recognized when flooding events take place in thepopulated flood plains, since the in-channel flooding, although more frequent, is alsomore limited and therefore more easily controllable and manageable. Theirrepetitiveness in time can nevertheless progressively lead to a threshold situation andtrigger catastrophic effects.In any case man-built infrastructures, including flood-protection works, can beseverely damaged owing both to riverbed in-channel highwater flows and to extra-bedflows: flooding, erosion and deposition inside and outside the riverbed are the^This work was done with the support of CNR-IRPI (Torino) services and includes the collaboration ofE. Beretta for the archives of aerial photographs and historical data, C. Novellone for the internal library,P.G. Trebo for the photo reproduction and E. Viola for the cartographic drawings.

processes defining watercourse hazard; the rate of the phenomena conditions theintensity of the effects produced on the territory (Fig. 29).An incorrect perception of river instabihty phenomena (Shumm, 1994) can leadto erroneous assessments of hazard conditions (Govi, 1980; Sear et al., 1994; Piegayand Lama, 1995; Simons and Downs, 1995), especially in forecasting progressiveeffects linked to flood wave propagation.In particular, with embanked rivers in a large natural flood plain, man forgets the93Fig. 29. Bridge on the River Po which collapsed owing to bottom erosion during the November 1994flood (at the top a 1981 picture (courtesy of C. Falco); at the bottom the riverbed lowering is marked bythe sill along the piles' alignment).

94tendency of a protected area to be submerged by flood waters and the possiblebreaking of an embankment causes disastrous floods (Govi & Maraga, 1995). On thecontrary, geomorphological memory preserves on the territory the physical traces ofthe abandoned river forms that condition the overbank flows. Shapes and sizes ofgeomorphological forms have to be considered as the integrated product of the naturalactions of in-channel waters, geological factors, meteorological conditions and man'sactivities. In particular, the width of the major riverbed formed on alluvial depositshas been shown to conform in its dimensions to the hydrological history of thewatercourse, whilst the channel pattern reflects the sedimentary conditions of the cutthroughalluvial deposits. Figure 30 shows three typological situations of physicalflooding systems that are representative of: a) aggradational single-thread system; b)deepening single-thread channel system, composed of several flooding levels; and c)multithread channel system.The presence of embankments on the alluvial plain of single-thread systemsconfines the highwater flows within artificial levees whose breaking can cause vastinundations depending on the amount of flooding waters and the extension of the lowlands. In particular, in the aggradational single-thread system, the flood determinedby the breach of the embankment is transversally propagated according to thegradient of the plain along directions with no possibilities of return downstream intothe former river channel and the flooding currents go out of their original waterleveeovertoppingstage^^f^ floodinginundation bybreachingFig. 30. Topographic sections of flood prone areas with trends of inundation caused by embankmentbreaching with a small flood corridor in a meandering channel: a) prograding alluvial plain along the riveraxis with a large flood corridor in a wandering channel; b) alluvial plain with incipient river terracing;c) torrent flood plain.

course. In the erosional single-thread system and muhithread system, the currentstransfer downstream according to the system's dominant flow direction.In the specific situation of confluences embanked in an alluvial plain between anaggradation tributary system and an erosive one, the geometrical situation of the alluvialplain and of the connected hydrographic junction can increase the risk conditions(Maraga, 1986). Indeed, the embankment of the main channel can create a dam effectobstructing the downstream propagation of a flood coming from a tributary (Figs. 31,32). The comparison between the two pictures emphasizes the twofold damming roleof the river embankments, that of flood propagation confinement and that of drainageobstruction of flooding waters coming from the tributary.Often anthropic factors determine an acceleration of the evolutive fluvial system,as in the case of channelisation which produces a higher velocity of flood wavepropagation, with effects such as producing worse damages at longer intervals.The geomorphological instability of fluvial territories, affecting both the riverbedand the alluvial plain, depends on the propagation patterns of the highwater wavesalong the river course and their frequency.If the frequency of floods is defined by meteorological events, the wavepropagation patterns, under the same hydrological conditions, reflect the conveyanceof the fluvial physical system, defined by the geometrical parameters of thehydrographic network and channel cross sections. With flood waves exceeding theordinary channel discharge, the alluvial plain behaves as a temporary waterway whoseboundaries can correspond with natural scarps in a mountainous territory or terracedvalley floor, or with structural embankments raised for the containment of highwatersin the open plain.During the overbank flooding a river's hydrosystem is composed of at least twopatterns of wave propagation: the main channel and its flood prone area. Since thefluvial physical system is open to many variables linked to interdepending natural andanthropic factors, its answer to flood dynamics and velocity of adjustment variesaccording to local conditions. Hydrodynamic variations leading to flood events cangenerate hazard processes of different magnitude according to the scale of the event:channel, alluvial plain or hydrographic network.Flood recurrence times differ according to whether they are confined within thechannel or flooding the alluvial plain. In the first case they usually show a return timefalling within a 5-year period and can cause variations along the bank lines; on theother hand in the second case they show return times of a few decades and canproduce variations in the fluvial course or in the topographic surface of the alluvialplain. Finally, flood events with secular or multisecular recurrence generally producedisastrous effects.Fluvial instability implies three types of geomorphological modelling:— planimetrical variations of the bank line due to channel form mobility with floodplain loss or addition (Fig. 33);— altimetrical variations of the topographic surface due to flooding with scouringor deposition;— textural variations of the drainage network due to new erosional processes of the95

96Oo

Fig. 31. Vast flooded area confined by the river embankments in a case of wide controlled expansion offlood waters (River Po at 250 km upstream of its outlet into the Adriatic sea, October 1977). Rightwardflow (mosaic of vertical aerial photographs, by permission of S.M.A. no. 429, 27 Oct. 1995).97channel with drainage increasing.The probabiUty of these processes taking place within a given territory depends onthe morphological features of the watercourse at the flooding stages.3,4.2.2 Main channel shapingThe main runoff riverbed can be subject to instability processes at the channel crosssection during highwater flows which have the capacity to mobilise the sediments^fIPo leveeColtarotownFig. 32. Inundation of inhabited centres in the mid-Po Plain: owing to the presence of embankment (1),the tributary flooding waters cannot be drained. The inundation was produced by the River Taro duringthe secular flood of November 1982 and affected a 70 km" developed area downstream. Rightward flow(mosaic of vertical aerial photographs, cone. S.M.A. no. 429. 27 Oct. 1995).

981889 ,,--'S iJililiii^lood plain loss« H^H flooci plain additionFig. 33. Planimetric mobility of the riverbank line with 0.5 km range of soil erosion and 1 km onacquisitions along the River Po wandering channel downstream of the confluence with the R. Ticino 400km from the outlet in the 1955-1988 period (courtesy of F. Dutto. modified).from the river bottom and banks, thus generating transport of unconsoHdated deposits.The frequency of these discharges defined as formative, generally shows return timesof around two years and corresponds to flows occupying the full width of theriverbed cross section (Riggs, 1976; Caroni & Maraga, 1985; Wharton et al., 1989;Kennet & Wahl, 1984).The magnitude of the phenomenon is linked to sediment transport and dependsboth on the duration of the formative discharge and on sediment availability. Thewater level, sediment particle size distribution and the local riverbed gradient, allcontribute to the sediment entrainment, whilst the availability of a sediment dependson the sedimentological conditions of the riverbed.The riverbed shape reflects the sediment transport mechanisms which are variableaccording to the particle size distribution of the alluvial deposits. In gravellyriverbeds, bed load and debris flow takes place in the multithread system, whilstselective transport takes place in straight channels and in transitional channels.The entrainment of alluvial materials and their deposition inside a riverbed occursby means of erosional or depositional processes and bed forms construction whosesize and distribution reveal either cutting or filling effects in the riverbeds. In the firstcase, risk situations are generated owing to the possible presence of works within theriverbed or to destabilisation of the structure following selective bottom erosion. Inthe second case, risk situations are more likely to be found with works located in thefluvial territories surrounding the riverbed owing to lateral bank erosion and consequentsoil removal. In fluvial stretches where the river bottom is in proximity to thebedrock, lateral erosion of the bank is the only possible action during the floods.Instability phenomena in the main discharge channel produce modificationsaffecting both the bank line and the fluvial axis; they characterise fluvial activity bothin the short term on a segment scale, within the evolution of the riverbed forms, andin the long term on a catchment scale, as part of the hydrographic network evolution.3.4.2.3 Channel pattern mobilityChannel pattern mobility expresses the freedom of a watercourse to accomodate its

hydraulic geometry parameters with the variation of water levels, according to thelocal and temporary hydrodynamic equilibrium conditions during flood wavepropagation. This mobility occurs on the bank lines with different patterns in relationto the channel type which, in turn, is different on the various river stretches ofvariable lengths. Finally, cross section parameters are related to the slope change ofthe longitudinal profile.Form mobility in space is always related to a channel pattern and coincides intime with formative discharges flowing near the bankfull stage. The formativedischarge activating sediments mobility is greater in the multithread system than inthe simple or composite single-thread system since it depends on the width of themodelling form. Therefore, under the same flow rate conditions, a single-thread formis more mobile than a multithread one, since the former concentrates water flows intoone channel, and produces variations linked to the bank line, whilst the latterdistributes water flows into a network of smaller interlacing channels, with the effectof reducing the water stage peaks and thus the sediment movement.The most unstable form in the single-thread system is the transition form definedas wandering (Neill, 1983) or transitional (Carson & Griffiths, 1988), whichcorresponds to an irregular-meandering channel with a gravelly riverbed. This formmay be interpreted as a stage of evolution from the multithread system to the singlethreadone in gravelly sediments induced by selective transport which can beactivated owing to an insufficient sediments supply (Cunge, 1985; Maraga, 1989,1992). In the alluvial plains on which an artificial floodway zone has beenimposed, the flood water levels derived from the presence of embankments are higherthan those of a free flood plain and increase sediments mobilisation within theriverbed.The instability of this transitional form usually affects bank scarps made up ofgravelly sediments in the lower part and sandy ones at the top and is produced by themobilisation of gravels. The phenomenon is often associated with a forking of theflow water in correspondence with transversal or median gravelly bars formingincipient pavement. The formation of a new main channel can be determined by theocclusion of the former channel with an inversion effect in the cross section: this isa typical phenomenon occurring in torrential watercourses (Quesnel, 1957). In thiscase the position of lateral erosion advances according to occasional rather thanrepetitive geometrical characteristics, affecting in time all the bank line over fewkilometers onto the plain (Dutto & Maraga, 1993). When the wandering channelcorresponds to a channelisation phase in the alluvial plain with a planned floodway,the meander chute cutoff effect is then possible, with upstream occlusion of themeander bend by episodical deposition on its talweg (Figs. 34, 35).In the case of exceptional flooding, the form's instability appears enhanced inthe flow forking processes which, during the propagation of a flood wave, can reconquerthe previously abandoned ancient courses of the original multithread system.3.4.2.4 Channel network adjustmentThroughout the hydrographic network the fluvial system is integrated with the slopes99

100'*^00^'ti»*^*'Fig. 34. Meander chute cutoff (arrow) during the flood that produced it. River Po 570 km from the outlet,May 1977. Rightward flow (Cone. S.M.A. no. 107, 24 Mar. 1980).by means of watercourses of progressively decreasing order, in relation to thediminishing area of the feeding catchment basin. The network is considered as a setof inter-connected fluvial segments, with a structure controlled by the principles ofenergy dissipation transporting both water and sediments downstream (RodriguezIturbe et al., 1992; Ohmori and Shimazu, 1994). The instability phenomena of themain runoff channel, of any kind or size, induce variations along the network andtherefore modify the propagation velocity of the flood waves.The network's geometrical variations can occur according to the two followingpatterns:— temporarily, during catastrophic flood events caused by overbank flows controlledby the distinctive features of the alluvial plain along directions not corresponding

101Fig. 35. Wandering channel form originated by the evolution of an original multithread system in theRiver Po at the confluence with the R. Tanaro. The activation of abandoned channels induced a diversion(a) of the secular flooding of November 1994 towards the inhabited centres of the left side, thus producingtwo embankment breaches (b): meander lobe with water reflux (c); (1) embankment (Cone. S.M.A. no.107, 24 Mar. 1980).to the direction of the channels axis;— permanently, owing to the stretching and shortening of single segments, or to anincrease of their density due to the new formation of first-order segments orchanges of the flow path; the latter are localised at the confluences and headpoints of lower-order watercourses.The causes of instability which produce permanent effects on part of the network,also induce adjustments on other sectors of the basin over long periods and with flowrates even smaller than those that caused the initial sudden occurrence of thephenomenon.3.4.2.5 Headward erosionFirst-order watercourses are involved in debris flow phenomena with the triggeringof small superficial landslides at their heads or on the lateral slopes, induce in the

1033.4.2.7 FloodingThe velocity of propagation and the height of the wave at peak discharge are directlyresponsible for the magnitude of the effects producible in highwater conditions. Thepresence of flood-prone areas around the main channel, however, produces a waveattenuation with water spreading by overbank flows onto the flood plain. Thelongitudinal and transversal components of velocity and the organisation of flowswithin this complex system of the channel and its flood plain have been investigatedduring the last few years by means of physical laboratory models (Sellin, 1995) andapplications to case-studies along selected river courses (Archer, 1989; Magillian,1992; Caroni et al., 1994; Myers & Lyness, 1994).During a flood event, a watercourse shows wave transfer patterns which differaccording to the size and planform of the riverbed, which can be particularly markedif multithread and single-thread channel systems are compared (Caroni & Maraga,1994). This is shown by the flood wave dynamic behaviour which affects both thepropagation velocity wave and the amount of flooded, according to the geomorphologicalcharacteristics of the hydrosystem.In the multithread system, the propagation pattern shows a direct variation withFig. 37. Alluvial fan instability in Alpine territory: a) block deposition in apical sector with channel avulsion;and b) fine-grained sediment deposition in distal sector with erosion processes. Case of an alluvialfan remobilised during September 1981 flood in the lower Val d'Aoste, North-Western Alps, in the TorrentRenanchio at the confluence with Dora Baliea, rightward flovs (cone. S.M.A. no. 429. 27 Oct. 1995).

104'^^^^m^m,^>^4J"•r^S^cf^-m^Fig. 38. Activation of temporary flood channels at the outlet with the alluvial valley floor. Confluencesof the Diveria (1), Isomo (2), Bogno (3) and Melezzo (4) streams into the River Toce near Domodossola,immediately after the flood of August 1978 (cone. S.M.A. no. 429. 27 Oct. 1995).the flow rate increase, whilst in the single-thread system a marked decrease duringoverbank flows is recorded (Fig. 39). This means that with equal water volumes amultithread segment can convey the flood flows downstream without noticeablymodifying the wave's shape, whilst a single-thread segment can cause a attenuationof the peak discharge.The flooded area increases progressively during the rising of the wave in themultithread system together with water levels; in the single-thread system, on thecontrary, the areas show a moderate increase when overflow begins, due to the expansionof the waters in flood-prone areas.Such propagation behaviour of the flood wave is justified by a fluvial hydrosystem'spropensity to distribute the high flows in more or less large flooded areaswhose extent varies according to the corresponding widths of the channel system; thewave is thus attenuated with peak discharge mitigation effects relative to the floodpronearea available. The multithread system allows several channels to be activated,even simultaneously, offering a wide space to the in-channel flows, so much so thatit can limit, if not exclude, overbank flows. The single-thread system, on the contrary,is composed of two separate hydrodynamic phases: within the river channel and/orin flood-prone areas, with overflow discharge that can occasionally exceed the inchannelflows, in accordance with the local geometrical conditions of the flood plain.The geomorphological setting of the flood-pronearea conditions the aforementionedmitigation effects of the floodwave peak. Indeed, a terraced development at differences

1052.5liii^^w 1.5E£a>>0.51 +-•— meandering-a— braiding0 A 4- H- •4- -h H0 500 1000 1500 2000 2500 3000 3500 4000Discharge (m^s"MFig. 39. Graph of the mean flow velocity during a simulated propagation of a flood wave for dischargesof 50—4,000 mVs affecting a multithread and single-thread system. The graph shows the reversal of trendof the curve obtained for the meandering system in correspondence with the sudden velocity decreaseinduced by the water expansion in flood plain by overbank flows (courtesy by E. Carani).in level of even some decimetres can define a natural order of zoning with subsequentdegrees of flood control, corresponding to areas of subsequent dissipation. Uniformdevelopment on a given level, however, creates continuous dissipation by overlandflow, unless intervention works are carried out to create artificial floodway zones.Figure 40 shows the development of flood-prone areas corresponding to givenflood stages in the cases of an aggradating or deepening single-thread system and inthe case of a multithread system, referred to case-studies of flood-prone areas in thePo Plain, extending respectively over 70, 60 and 20 km^ (Maraga, 1990).B£ c 3514HO£ 2LZI7—— I —50a— b-- c-r100Flood prone area (%)Fig. 40. Graph of flood plain zoning levels in relation with the corresponding flooding stages: a) and b)embanked alluvial plain with single-thread aggradeting/deepening channel; c) unconfmed alluvial plainwith multithread channel. The presence of embankments increases the number of zones with areapercentage steps observed outside the embankment (maximum in a), flooding stage 5.

1063.4.2.8 InundationThe aspect of fluvial hazard which most affects the physical arrangement of aterritory and has the most serious effects on its management is the inundation of thenatural ground surface. This is in direct relation to the extension of the areassusceptible to the instability phenomenon, to the recurrence interval and to therapidity with which the inundating process is exhausted.As a consequence of the inundation produced by extraordinary water volumes, thefollowing effects can be determined on a territory:— of temporary nature, concerning the water flooding, where the extension and thepersistence of the inundation depends on the plain morphology, considering alsoany man-made structures;— of permanent nature, concerning the erosion or sedimentation forms in theinundated areas: the prevalence of one or the other is controlled by the slope ofthe surface affected.The suddenness of an inundation phenomenon affects the development of morphologicalprocesses and determines the degree of seriousness of any damage producedby the event. This usually occurs on a mountainous valley floor or alluvial fanenvironment, where peak waves propagate along flood plain slopes with gradientssimilar to those of the channels. On the wide plains, on the contrary, where thewatercourse is laterally confined in an artificial flood way zone and the inundationcharacterised by sudden overflow can be determined by a breach in the embankment.A long recurrence of inundation due to breaching of embankments concerns thegreat alluvial plain of the River Po (Govi and Turitto, 1993), with historical recordsquoted in chronological lists and in official articles of the Ministry for Public Works:the events listed started from the eleventh century. The location of the inhabitedcentres directly affected by floods is shown in Fig. 41 (Govi and Maraga, 1994). Theworst most recent flood struck the lower territories of the Po Plain in November1951, claiming 80 lives. This flood was exceptional owing to the extent of theinundated area (1,000 km^) and was caused by three successive breaches occurringwithin 3.5 h along a total of 3 km of embankment, facing two inhabited centres: theflood sediments covered over 8 km" of urban and farming land, with sand depositsup to 3 m thick near the breaches.In the nineteenth century the Po Plain was already defended from floods bymeans of a continuative system of embankments along a 400 km course from themouths of the Po upstream and its management was already aroused interest in thecivil engineering field (Comoy, 1860). A peculiar geomorphological criteria of settingthe embankment lines affected the flood way configuration which is very irregularas a consequence of the watercourse's evolution: the embanking lines are near theriverside in the case of aggradational single-thread system or far away from theriverside in the case of erosional single-thread system, with average widths of theembanked flood-plain area of, respectively, 0.7 and 4 km. This reflects the primaryprotection system laid down centuries ago, in accordance with the contemporarymorphological situation of the watercourse.

107ULi>XUJCOP"-5o

108Fig. 42. Evidence of flood plain splay with local scour (arrow: a) after a secular flood; circle shows thebreak in the main railbed whose layout crosses a meander bend cut off over one hundred years ago. RiverTanaro during the flood of Nov. 1994 (cone. S.M.A. no. 429. 27 Oct. 1995).

109The presence of abandoned riverbeds near the floodway is associated with thehazard of breaches caused by water infiltration under the embankment, since in theseplaces the alluvial deposits are characterised by a coarser and more heterogeneousparticle size than the surrounding sediments, thus making up a preferential site forthrough flow processes. The abandoned riverbeds, even at a considerable distancefrom the watercourse, control the overland flows. For example, in the mid Po Plaina historical flood of 1705 occupied the surrounding land over a 20 km wide area,distributing its waters along channels parallel to the valley axis, in accordance withthe traces of abandoned riverbeds dating from the Bronze Age onwards (Castaldini& Piacente, 1995). During the more recent flood of November 1994, which affectedthe upper Po Plain basin, serious damage to man's infrastructures was recorded justin correspondence with ancient river courses which had been activated by greaterinundation currents during the propagation of the highwater (Fig. 42).In the presence meandering river course, controlled by the uninundable terracescarps, such as in meanders cut deeply or confined by embankments, the riverbedmobility is in marked contrast with the relative staticity of the imposed natural orman-made limits. The scarps and the embankments are always subjected to theerosion caused by the meanders' evolution within the floodway zone. In the case ofembankments, the meanders traces convey the overbank currents straight onto theembankments and generate breaches (Fig. 43). As one of the river processes linkedto the modelling of a watercourse which can induce a flood hazard situation due tothe breaching of an embankment, bank erosion should be mentioned. It is producedby both the downstream migration of meander bends and the deposition of sediments|>;i.5|-;;:'| embanked floodway zone'~Vv. o'C channel%^ breaching sites '^^^^ ^^^^ active channelFig. 43. Meandering trend of a watercourse and related flood plain zone bounded by embankments: situationof the River Po during the XIX century in the stretch near Piacenza 350 km from the outlet. Themost recurrent breach situations are located in correspondence with abandoned channels, internal orexternal to the embankments.

110within the riverbed, with the consequent formation of middle bars or islands alongstraight courses or downstream of confluences.The assessment of the inundation probability, based on the flood recurrence,should take into account, for a given investigation territory, the morphologicalchanges of the riverbed and alluvial plain as well as the development of man-madeinfrastructures. Previous instability phenomena, caused by inundations, could nolonger represent hazard situations, whilst new hazard conditions could be generatedowing to the mobility of the fluvial system.3.5 Marine hazard3.5.1 Geomorphology3.5.1.1 Coastal environmentA coast is a stretch of varying extension between land and sea. It comprehends theshoreline which has a changeable morphology in space and time, according to shortand long-term fluctuations caused by sea-level variations due to several causes: fromthe flux and reflux of waves and tides to the regional or worldwide changes of thesea level caused by tectonics, eustatism, etc.Among the processes that shape a coast, those involving waves are the mostimportant. There are various ways in which waves break a shoreline. First of all, ifa coast is not a sheer drop from a cliff to the sea, the waves approaching it lose someof their propagation velocity owing to friction on the shallow sea floor. In otherwords, if the wave approaches the coast in an oblique direction with respect to theisobaths, the wave portion that first reaches the shallow bottom undergoes aslowdown due to friction. Therefore, wave fronts tend to arrange themselves parallelto the isobaths, i.e., the direction of the wave energy tends to assume a directionnormal to the coast. This phenomenon is named wave refraction (Fig. 44). As aconsequence, wave energy is concentrated towards headlands and promontorieswhereas it is dispersed in bays and inlets.Besides undergoing a diversion of their fronts owing to wave refraction, whenwaves come in contact with a shallow sea bottom a deformation of their oscillatorymotion also occurs with overturning of the crest into the hollow in front of themcreating plunging breakers. The water is thrown forward and goes up the coast as faras its transport energy allows. Afterwards, the water returns down the shore to the seaunder the force of gravity, with a more or less disorderly and forceful landward flow,called backwash.Although the waves hit the coast, although with reduced energy owing to frictionand with a direction diverted by refraction, they are also subject to a process ofreflection with an angle equal to the angle of incidence. As a result of the interferencebetween the two wave systems, direct and reflected, a fairly complexcomposite wave is produced.The incident wave, to some extent diverted by refraction, the reflected wave and

Illivai/e segments of same energy in deep waterA B CFig. 44. Wave refraction, due to the concentration of wave energy on headlands and to the dispersionaround bays, has an important influence on erosional and depositional processes affecting coastlines.the backwash all have different angles and directions and determine a compositelandward and seaward movement with a zig-zag trajectory, subparallel to theshoreline, called longshore current.Coastal regions, in particular those in direct contact with the sea, are characterisedboth by high humidity, owing to the constant presence of sea water and by scarcenessof vegetation, owing to the saltiness of the air. These two characteristics create veryparticular conditions, quite different from those of other environments where abundanthumidity is accompanied by luxuriant vegetation. In this way processes ofconcentrated and widespread runoff take place, as well as landslides and solifluction,owing to littoral rock and debris impregnation.Moreover, the presence of sea water is a cause of important and widespreadphenomena of physical and chemical weathering of rocks: salt cracking, humidification,frost shattering, solution, hydrolysis, hydration, etc.Wind, besides being a wave generator, is an important agent which transports seawater towards territories not otherwise reached by the waves and also sand along thecoast or to the inland in the form of littoral dunes.Tides are an important modelling agent. These periodical variations of the sealevel along a stretch of coast (intertidal zone) are the cause of several processes: saltcracking, humidification-exsiccation, etc. They also broaden the zone subject to wavemotion. Finally, with the rising and lowering of tides, conspicuous horizontalmovements of masses of water, called tidal currents, take place. These are veryimportant agents of sea-floor erosion, sediment transportation and deposition.

112especially near harbours, bays and, in particular, lagoons and estuaries, where theyadd to the effects of fluvial currents.Rock characteristics, such as cohesion, fissuring, frost shattering susceptibility,permeability and cementation can favour littoral marine degradation to varyingextents. Also particular tectonic arrangements may condition a coast's degree ofstability; for example, a dip-downstream attitude can facilitate rock slides.Animal and vegetal organisms are a direct or indirect cause of several physicaland chemical processes when alive: roots widening joints, animals such as datemussels digging through rocks either mechanically or by secreting acid substances,coastal plantations damping the wave motion, corals and calcareous algae buildingatolls and reefs, micro-organisms producing carbon dioxide and thus causing karstphenomena, etc.3.5.1.2 Coastal processesSimilarly to river erosion, diverse morphogenetic processes linked to the action oflittoral sea waters are defined by the term coastal erosion. Like the categoriespreviously defined regarding watercourses, four types of coastal erosion can bedistinguished:Coastal erosion in the strict sense, means the removal and loading of detritalmaterial from a sea shore.Cavitation means the mechanical action of the waves only against the coast.Abrasion means the mechanical hitting action of debris thrown by the wavesagainst the coast.Coastal degradation is a whole complex of morphological phenomena linked tothe presence of the sea. For example, the weathering of rocks owing to humidificationand exsiccation or salt cracking processes determined by marine water; or massmovements following undermining activities at the toe of a sea cliff, etc.The load of marine waters is made up by organic and inorganic materials insolution and by detrital elements of the most varied dimensions. Only a smallportion of these is derived from actions of direct coastal erosion; in most casesthey are conveyed to the sea by watercourses, glaciers, winds, etc. Part of thisdetrital material undergoes wearing due to the movements of the sea, or istransported and finally abandoned off-shore or transferred from one point of the coastto another.As happens with fluvial currents, transportation trends and conditions depend onthe one hand on marine water velocity, turbulence, density and temperature and, onthe other hand, on the dimensions, nature, bulk density and shape of the materials.Solid matter can be transported in solution, in suspension, hy floating, saltation,rolling and dragging along.Marine currents transport solid matter exclusively in solution, suspension or byfloating; tide or longshore currents may assume noticeable rates of velocity andturbulence and thus can transport also by rolling, dragging or saltation. The latter istypical of plunging breakers which have considerable kinetic energy. Backwash cantransport even coarse materials, by means of rolling, dragging and saltation.

113The deposition of the detrital load transported by sea waters may occur owing toa decrease of a current's energy, as happens with fluvial currents.In certain cases the deposition takes place owing to the interference of twocurrents having opposite directions, following the ''algebraic" annulment of theirkinetic energy, as in the case of two opposite and contrary wave fronts meeting asan effect of wave motion refraction, or caused by the interference between coastalbreakers and backwash current, or between tide ebb and fluvial current, etc.The movements of the sea, in particular wave motion, rearrange and distribute thegrains of solid matter which are progressively deposited along the coast: in this waylittoral sands seem to be "washed", that is deprived of finer silty and clayey elements.These finer particles are, however, present in fluvial deposit sands whose patterns ofsedimentation and transportation make their removal more difficult. On the otherhand, coarser elements can mix with littoral sands since, once they have beendeposited by waves, they can hardly ever be removed by backwash.3.5.1.3 CliffsA marine cliff (Pig. 45) is a rocky bluff, generally without vegetation, in contact withthe sea. It has a steep or even vertical slope angle and is created by the direct orindirect erosive action of the sea. Marine cliffs are found in competent rocks but alsoin sands and clays. On the other hand, not all steep or rocky coasts are cliffs: thereare cases of false cliffs which have not been modelled by the sea but by otherphenomena, such as scarps along littoral faults or subaerial erosion coasts submergedowing to transgression movements.A distinction should be made between live cliffs, at present in straight contactwith the sea and subject to marine erosion, and dead cliffs, no longer active andseparated from the sea by coastal deposits or an erosional shore platform.Erosion, in a broad sense, and the dismantling and retreat of a cliff all depend onboth littoral abrasion and cavitation and the removal of debris, as well as thedegradation phenomena due to the sea. Moreover, the processes depend on the typeof wave motion, tide extension, rock resistance, the topographic features of theshoreHne, the steepness of the submerged scarp, the quantity and particle sizeFig. 45. Schematic example of a cliff profile.

114distribution of the detrital materials transported, etc. An essential role in a cliffsmorphological evolution is played by several characteristics: a difference in thedegree of competence gives more or less steep profiles; mineralogical compositionmay favour to varying extents chemical weathering and therefore a scarp'sdegradation and retreat; the degree of homogeneity or the alternance of differentlithological types conditions a cliffs shape; the strata's tectonic attitude or thepresence of joints determines more or less steep and indented coastlines.The retrogradation mechanism of a cliff might be schematically simplified asfollows. The starting point is given by a cliff of unspecified origin in direct contactwith the sea: the processes of weathering increase the number of fissures and causea certain fragmentation of the rock; at the same time the actions of cavitation andespecially abrasion effected by coastal breakers dig a notch in correspondence withthe mean sea level; after a certain lapse of time the fall of a portion of rock can occurin correspondence with the steepest and most fissured stretch of sea cliff The fallendebris which accumulates at the cliff's toe for a time protects the scarp from theattack of coastal breakers. The latter in the meanwhile gradually reduce the rockfragments by means of abrasive processes linked to the waves' landward and seawardmotion; the smallest detrital fragments are progressively removed, owing to theerosive effect of the waves and in particular longshore currents. As the accumulationcovering the cliff's toe is gradually dispersed, meteoric degradation may continue toproduce and/or increase rock fissuring in the scarp. Moreover, the breakers' actionscan dig a new notch and reestablish the morphological situation described at thebeginning: thus, a retrogradation process may start all over again.Retrogradation of sea cliffs may occur with extremely varying rates: fromimperceptible to 10 cm/year. Therefore, with other conditions being equal, theevolution of cliffs depends on the erosion processes which break up and demolish therocky walls, those which determine a reduction and removal of the debris and finallythe weathering process, and in particular the actions of marine waves and currents.Nevertheless, an important role seems to be played by the more generalmovements of the sea, i.e., fluctuations of its level in either a transgressive orregressive sense. Indeed, the retrogradation 6f a marine cliff leads to the formationof a wave-out erosional platform (Fig. 45) whose progressive extension obstructs thecoastal breakers. The latter gradually lose their erosive power as they come to attackthe cliffs toe since friction with the platform disperses a considerable portion of thewaves' initial energy. If the general movements of the sea or, rather, the relativemovements of sea and coast tend to a transgression, the evolution mechanism of seacliffs does not stop, but the cliff is more and more subject to retrogradation, leavingat its toe an erosional shore platform which is gradually submerged by thetransgressive sea. If on the contrary the movements are regressive, then the sea cliffcannot be lapped by the waves any longer and thus turns in time into a "dead cliff.In some cases cliffs have vast and irregular cavities of varying dimensions:notches, caves, arches, etc. Their origin can be due to physical or chemicaldegradation processes or to differential marine erosion of lithological types of varyingresistance or rock portions having different degrees of fracturing. In limestones the

115origin is often related to karst solution phenomena, simultaneous with or precedingcoastal erosion processes. Sometimes the waves' action can isolate large rocks andstacks from the cliff.Usually a jagged and irregular coast with bays and headlands is subject to aregulation of its shoreline: in fact, owing to wave refraction beaches are formed onbayheads whereas promontories are eroded, with consequent attenuation of theembayed shoreline. Subsequently, baymouth bars, spits and erosion platforms developfurther reducing wave energy towards the coast thus favouring littoral sedimentation.The latter takes place according to processes and landforms mainly governed bylongshore currents.In some places, however, especially in correspondence with more or less resistantrocks, selective littoral erosion occurs which progressively forms and accentuates amore or less regular coastline.3.5.1.4 BeachesThe term beach is given to a littoral belt made up of present and recent cohesionlessmarine deposits. Seaward it is bordered by the low water zone called offshore andlandward by sand dunes and the first bedrock outcrops (Fig. 46). A beach issubdivided into areas the first of which is called mshore. This is the portion rangingbetween the mean high and low-tide levels and the permanently emerged zone.Generally the inshore contains a low tide terrace and a surf zone. The lattercorresponds to the steepest portion, where surging waves and backwash movementsusually take place. The emerged beach is often longitudinally divided by a berm intotwo parts: the backshore and \ht foreshore. The berm is formed by an accumulationof materials abandoned by coastline breakers, beyond the backwash limits ofinfluence, where water goes back to the sea mainly by underground flow. It can beincreased also by the wind, depositing sandy material from the foreshore. Coasdinebreakers of particular intensity may erode the berm portion facing the sea. Thebackshore is made up of present littoral deposits and only exceptionally can it beinvaded by sea waters; in some places it contains shallow lagoons and on its surfacehouses and farmland can be found.In the offshore and inshore if the detrital material is not subject to violent actionsby the waves, it is removed and is moved slightly forwards, in correspondence withbackshore foreshore inshore offshoreFig. 46. Schematic example of a beach profile.

116crests, and backwards, in correspondence with wave troughs: typical oscillationripples can be observed. Along the surf zone, seaward current ripples are found if thebackwash movement prevails; on the contrary, if the advancing movements aredominant, landward current ripples are formed. The study of these detailed seaformscan be applied to reconstruct the dynamics of coastline waters.On the other hand, when the plunging breakers are rather forceful, the grains ofmaterial are bluntly raised by turbulent movements: some are thrown on the emergedbeach and others slowly fall down onto the sea floor. Backwash currents can removethe finest particles and carry them off-shore; they can also easily transfer thosematerials which, raised by the wave motion, stay for a while in suspension near thesea floor. The debris, once removed, transported, deposited and again removed,undergoes a continuous alternating landward and seaward movement, with trajectoriesvariable in space and time, depending upon the waves' direction and energy, the forceof backwash, the direction of longshore currents, etc. Afterwards, it will be depositedin lower turbulence, lower current velocity zones or in points where a compensationof two opposite currents occurs.The general dynamics of a beach is usually characterised by an alternance of twoactions: an action of prevailing accumulation of debris and an action of erosion in astrict sense of the material. The alternance rhythms of these phases are extremelyvariable: daily, several days and so on up to completely seasonal.Indications of the degree of stability of this type of coast are derived from theequilibrium between supply and removal of detrital material. If the balance is equalover a certain time, then the beach may be considered stable.On the other hand, beaches can be affected either by progradation or retrogradation,whether the supply of material or its removal prevails. Particles are selected bywaves according to their dimensions, weight and shape. The coarser ones, which areusually heavier, are abandoned on the beach, whilst the finest ones can be taken back,transported and deposited off-shore. The material can also be thrown by plungingbreakers beyond the high tide limit or, in any case, beyond the sea level at thatmoment: if backwash does not take place in this stretch of beach, because thebreakers' water goes back to the sea through underground passages made up ofdetrital permeable layers, even the finest debris can remain on the beach.As a consequence, the dryer and the more permeable a beach is, the more theprocess of sedimentation, and therefore of progradation is accentuated: this fact caneasily be observed on Mediterranean beaches in summer. On the contrary, duringrainy periods, especially with high and frequent waves, the beach sediments aresaturated with water and therefore become practically impermeable; as a consequence,all the water goes back to the sea through the subsoil, with velocity directlyproportional to the beach gradient. Moreover, rain water can add to sea water, thusincreasing the erosion power in a strict sense and the transportation of backwashwaves. To all this, also the removal and undermining action of plunging breakersshould be added, with the increased likelihood of debris being taken on load by thewaves, since the energy necessary to keep a detrital element in movement is lowerthan that required for its removal from the state of immobility.

For these reasons many beaches are subject to erosion activities in winter: on theone hand great plunging breakers and backwash currents attack and demolish thebeach and shoreline bar, on the other hand they convey to the sea part of the debristhat make up beach deposits.Generally in a prograding beach the prevailing sedimentation stage alternates withphases of partial erosion and marine and aeolian rearrangement. The debrisaccumulation on the seaward face of the shoreline bar causes progressive advancementof the crest, with consequent widening of the backshore.The beach slope gradient mainly depends on the size grade of its grains: finesands make up very gentle seaward slopes whereas coarse sands or gravels build quitesteep slopes:— 2° for 0.12 mm diameter sands:— 8° for 0.50 mm diameter sands;— 12° for 2 mm diameter sands;" 15° for 5 mm circa diameter gravels;— 20° and more for pebbles of 64 mm and over in diameter.It should be considered, though, that the slope angle depends also on the energy ofthe wave motion which, in turn, is partially linked to the longitudinal trend of thecoastline, its irregularities and the extension of the sea front.Preferential places for debris accumulation and therefore for beaches are the seastretches facing river mouths, because of the abundant supply of materials, or thebays and the areas between islands and coasts, owing to wave refraction.Sand dunes can be found landward, beyond the berm: they are accumulationlandforms due to wind action and are similar to those of arid regions. With the latterthey have in common a vegetation-lacking environment which favours wind deflationprocesses. The debris supply area is the beach whereas the accumulation area usuallycorresponds with the backshore or with inner stretches of coast, where the energy ofthe wind blowing from the sea is lower whereas the presence of vegetationprogressively increases.Seaward, opposite the beach, longshore bars can be found on the sea floor: theyare long and narrow submerged deposits, subparallel to the coastline. The patternsthat lead to their formation are complex, various and different. In some cases the firststage of their formation could occur in neutral zones, where waves and currents arecompelled to deposit part of their load because of the interference of oppositedirectionenergies. In other cases the deposit could be the result of progressiveslowdown of the waves owing to friction with the sea floor. This would lead to a lossof energy with consequent sedimentation of the coarser elements taken on load afterthe dismantling of headlands. In other cases they could be remnants of ancient bermssubmerged following marine transgression.Bayhead beaches are formed due to the decrease in wave energy owing to thephenomenon of refraction at inlets. The same phenomenon can also give rise to aneutral zone between an island and the coast, following the collision of two oppositewave energies, with consequent deposition of debris: the progressive sedimentationcan then build up a junction between an island and dry land with the formation of a117

118tombolo. Hooked spits are the result of littoral drift motion owing to a leeward windloss of part of the load transported following a decrease in energy. Cuspate forelandsare formed following the collision of two opposite directions of currents carryingdebris which is thus accumulated. Littoral barriers mainly derive from the emersionof a shorebar following the progressive availability of material.Lagoons are small bodies of water separated from the sea by littoral barriers ortombolos and are in direct and active connection with the inland fluvial network,since they are linked to the open sea by means of inlets, which are the starting pointsof channels going through the lagoons. In the lagoon there are marshy areas whichare nearly always emerged and covered by grass and shrubs, called schorre, andothers emerging only at low tide called slikke. In lagoons the reflux waters of tidalcurrents are added to the fluvial ones, thus freeing the bottom of the channels fromdebris.A lagoon's life depends on many conditions: the amplitude of tides, the flow rateand sediment load of influent streams, the dimensions and shape of the lagoon itself,the width of the mouths, the direction of marine waves and currents, etc. Within thesame lagoon a live part is distinguished from a dead inner part. In the latter the tidalcurrents arrive much reduced, the channels are transformed into closed-systemchannels where shores prevail over slikkes. When abandoned to natural processes,which tend to obstruct their mouths and to fill their basins with debris, lagoonsslowly subject tend to fill up going through the stages of dead lagoon, coastal marshand swamp.3.5.1.5 The evolution of coastlinesA coastline, whether marine cliff or beach, can show either a positive or negativebalance depending on whether the supply, that is the sedimentation phase, is superioror inferior to the drawing, i.e., the erosion and removal phase of the materials makingup a coast.Coastline supply can be derived from two different activities:— those resulting from the subaerial modelling processes of the mainland (especiallyfluvial, colluvial and aeolian);— those due to either the direct or indirect action of the sea (cliff dismantling andretrogradation, erosion in a strict sense, erosion of the continental shelf andbiological contributions, such as shells of mussels).Also the drawing of solid matter can be the result of two different activities:— elements taken on load near the coast, transported by currents and abandoned onanother coast or towards the open sea;— elements removed by aeolian deflation and dispersed over the open sea or farinland.The negative balances of coastlines, or the erosion of a coast in a broad sense, i.e.,when removal actions prevail over supplying ones, have various causes: natural andman-induced.Among the former wave refraction, causing the erosion of promontories, hasalready been mentioned. Other factors can play an important role, such as: climatic

119changes which modify the trends and amount of erosion and sedimentation in themainland and can also change the winds' trend; changes in the path of watercoursesnear their mouths with consequent modifications, haltings or new supplies of materialalong coastlines. Finally, eustatic, isostatic and tectonic marine transgressions shouldbe quoted since they lead to noticeable, although extremely slow, invasions on themainland by the sea. In most cases the latter are relatively slow phenomena,especially compared with human life, and hardly ever can they be adequatelycontrasted. On the contrary, the case of phenomena caused by man's actions isdifferent: in the last few centuries and with increasing intensity up to the present,many coastline areas of the Earth have suffered deep changes in their naturalequilibria, as a consequence of man's various activities. This has led to variousdegrees of alteration which can be defined in terms of impact (see chapter 1.5).3.5.1.6 Continental shelf and slopeThe connection between dry lands and sea floors takes place all over the Earth'ssurface along a stretch of territory defined as continental margin. Therefore, allcontinents are bordered by a continental margin which develops from the shorelineto the abyssal plain according to the following morphological units (Fig. 47): a)continental shelf; b) shelf break: c) continental slope: and d) toe of the slope.Whereas the origin and the structural attitude of continental margins reflect thegeodynamic features of the continents, the forms that characterise them show constantelements derived from the homogeneity of the geomorphic processes (erosional andsedimentary) which modelled them.For this reason, continental shelves show the following characteristics: mildlysloping erosion or accumulation surfaces up to a depth of 120 to 200 m, shelfmargins made up of a deeply convex surface formed by the prograding accumulationsof fine sediments; the slope is a high-gradient surface linking the margin with theBEACHINNER CONTINENTALLOWER CONTINENTALSHELFSHELF BREAK SLOPE ABYSSAL PLAINab^ c cLow stana sea-leveld \y,fa - submerged beachb - posidonia prainiec - beach rocksd - late quaternary depositse - olocenic depositsf - slumpings areag - slope deposits area\^ \ gFig. 47. Schematic example of a continental shelf profile.

120bathyal plain and, finally, the toe of the slope where the materials mobiHsed bygravity forces along the slope surface accumulate. Usually the bathyal plain is foundat a depth of 2,000 m and goes as far as 4,000 to 5,000 m.coastal hazardThe surface of connection between the continental shelf and the bathyal plain,with a difference in height of a few thousand metres, is essentially affected bygravitational geomorphic dynamics. The terrigenous sediments, which accumulatedon top of the slope also in the periods of maximum sea-level lowering in periglacialepochs, are normally found in unstable conditions, giving rise to slumping even oververy wide areas. Moreover, landslide events repeated in time in areas characterisedby high terrigenous intake from the continent produce turbidity currents along theslope, with high linear erosive energy. This phenomenon gives origin to deep cutscalled canyons, and can also be favoured by particular lithological and structuralconditions. Therefore, the canyon system of a slope reflects the morphodynamic andsedimentological structural characteristics of the whole continental margin. Alandslide originating at a canyon's head on the edge of the shelf produces a turbiditycurrent which can run for several kilometres along the whole cut, as far as the toe ofthe slope. Eventually the current reaches the bathyal plain where the materials insuspension progressively lose their energy and are deposited, forming large fans.Even without the presence of canyons, an accumulation of fine sediments isnevertheless produced at the base of the scarp making up the toe of the slope.3.5.2 The hazard"^*by Paolo ORRU' and Antonio ULZEGA'3.5.2.1 Coastal hazardThe problems related to coastal hazard are of considerable environmental importancebecause of their implications regarding risk: in fact, human activities now take placealong most coastlines, sometimes with continuity. A coastal environment which formany significant reasons can be used as an example is that of the Mediterranean Sea(Fig. 48). This sea is a semiclosed body of water localised at midlatitudes and notsubject to extreme meteorological and climatic events. Since the most remote timesits coasts have been a location favoured for human settlements. Over the centuriesthis has led to the creation of harbours, to urban and industrial centres, to hydraulicland reclamations, to the excavation and discharge of materials and so on in placesmainly chosen according to their physiographic characteristics. Usually these areashave also coincided with situations subject to rapid geomorphological evolution, suchas fluvial estuaries, peninsulae, coastal plains, lagoons, etc. Settlements, linked initiallyonly by sea, subsequently required the progressive construction of communicationsroutes of growing importance along the coasts: first roads and then railways.Along coasts the highest levels of hazard are due mainly to the followingconditions:'A. Ulzega has also written paragraph 3.5.1.6.

121Fig. 48. Location of quoted examples: 1) Capo Altano, cliff in rotational slide; 2) Baia del Poetto inCagliari, active cliff and beach erosion processes: 3) Baia di Carbonara, littoral erosion processes; 4)Muravera coastal plain, inundation processes in coastal plain and lagoon; 5) Venetian lagoon and R. Podelta, lagoon earth filling processes; 6) Ria di Olbia. fluvial progradation processes in a harbour area; 7)Gulf of Asinara, submerged paleocliff with rotational slide; 8) Capo Caccia. submerged paleocliff withrock falls; 9) Strait of Messina, unstable submerged paleocliff owing to neotectonics; 10) Gulf of Orosei,active canyon; 11) Gulf of Gioia, canyon's headward retrogradation processes; 12) Gulf of Taranto, scarpdeltaic processes; 13) Strait of Corynthus. scarp landslide processes owing to neotectonics; and 14)Channel of Sicily, sediment dynamics due to dragging currents,1) active geodynamics owing to neotectonics, volcanism, seismicity and subsidence;2) geological-structural attitude favourable to instability;3) high fluvio-deltaic and littoral sedimentation;4) high meteo-marine energy.3.5.2.2 Hazard affecting cliffsWith respect to marine cliffs, the hazard is linked to retrogradation, whose evolutionvelocity is function of:— energy of incident wave motion;— geological-structural conditions;— seismo-tectonic activity.In terms of geomorphological risk, the situations of highest hazard are found wheremass movements associated with retrogradation affect constructions on the cliff top's

122surface; as for people's safety, the risk consists in the possibihty of sudden falls fromunstable scarps.For example, the case of the Sella del Diavolo promontory, east of the townshipof Cagliari in Sardinia, is illustrated. It corresponds to a small horst made up of aMiocene sequence of sandstones which give way towards the top to marly-arenaceousUmestones and eventually to Tortonian calcareous reef banks. The coast shows atectonically-derived cliff which is morphologically active owing to the continuousundermining effect at its toe caused by sea waves. In different epochs, gravitationalphenomena of varying intensity have taken place, such as slumps, rock detachmentsand partial falls of the slopes. In proximity of the most unstable part of thispromontory there is a busy tourist harbour and a beach which is very crowded duringthe summer. This has led to situations of serious risk which lately have caused theloss of human lives. In order to mitigate the undermining process at the base of thesea cHff, the Ministry of Civil Defence of the Italian Government has constructed avast cliff which has locally reduced the direct risk but, at the same time, has triggerederosional processes in the nearby beach, with noticeable damage to seaside-resortactivities.In some places, also nonactive marine cliffs, that are no longer undermined attheir toe by sea waves can show conditions of potential instability, given by:— dormant deep-seated gravitational slope deformations;— fault surfaces.The geomorphological risk is often associated with works which owing to loadchanges or modification of the internal runoff, alter the scarp's conditions ofequilibrium.Deep-seated gravitational deformations consequent to Pleistocene variations of thesea level have affected the Capo Altano sea cliff, in south-western Sardinia, asillustrated in the block diagram of Fig. 49. At present, the direct sea action does notaffect the sea cliff; nevertheless the recent construction of a major coast road on theslip surface of an ancient landslide has determined its reactivation, thus causing thecomplete destruction of the work itself.Transport infrastructures and residential and industrial settlements along coastsaffected by uplift neotectonic movements, are particularly subject to risk, as shownby the accelerated retrogradation processes along the Italian coasts of Liguria,Tuscany and Calabria.3.5.2.3 Hazard affecting beachesAlong most of the Mediterranean coasts, a general increase of the erosional processesderived from the present rising of the sea level can be recorded. This phenomenonis particularly evident on beaches, where even minimal variations of the sea level caninduce large-scale effects.Inevitably, these phenomena are related also to vulnerability as the natural processof erosion affecting a beach can determine risk conditions for the works constructedin the high-beach active zone. Moreover, the concomitance of a natural event withunsuitable use of the beaches can exacerbate and accelerate erosional processes.

123Fig. 49. Capo Altano, south-western Sardinia — block-diagram showing the fossiHsed coastal rotationalslide from the "Eolianiti di Funtana Morimenta" (Middle Pleistocene). The recent construction of a roadembankment (a) in correspondence with the slip surface reactivated the slide which caused a partialdestruction of the works. Lithology: 1) marlstones. sandstones and conglomerates (Oligocene); 2) rhyolitictuffs (Oligo-Miocene); 3) ignimbritic lavas (Oligo-Miocene); 4) aeolianites (Middle Pleistocene); 5)aeolianites and colluvial deposits (Upper Pleistocene); 6) conglomeratic beach-rocks (Holocene); 7) sandycolluvial deposits (Holocene-Present); 8) sands and gravels from present beaches (modified after Orru &Ulzega, 1984).Finally, the construction of engineering works on the shore line could itself determineimmediate or subsequent impact effects, such as the long-shore dispersion of abeach's sandy materials, and therefore trigger accelerated erosional processes. In anycase, even if erosional processes do not coincide directly with the works, the loss ordegradation of a beach always means serious economic consequences.As an example, the case of the Poetto beach, in southern Sardinia, is nowreported. This beach originated during the Versilian emersion of a 10 km long littoralbarrier closing a complex lagoon system of Tyrrhenian-related backshore. The fullarea is no longer provided with the feeding of solid materials owing to the completechannelisation of watercourses, the presence of quarries in the riverbeds and theconstruction of reservoirs upstream. Moreover, since the Second World War the beachhas been subjected to the removal of several million cubic metres of sand used forthe building industry in both its submerged and dry portions. Over the past fifteenyears a general acceleration of erosional processes has been recorded; they haveproduced a 70 m retrogradation of the shoreline and a general lowering of the beachprofile. This new arrangement allows the coast roads and seaside resort areas to bereached by the most intense sea storms.With marine meteorological conditions of low energy, sandy residual depositswitnessing the presence of paleobeaches can be preserved, although in a precarious

124equilibrium. This is the case of Spiaggia del Riso near Villasimius, placed at thesouth-eastern extremity of Sardinia, where the particle size and chromatic characteristicsof its exclusively quartz grains made it famous as a seaside resort. The recentconstruction of a large tourist harbour nearby has altered the beach's dynamicequilibrium, causing total removal of the sand. The extremely rapid erosional processoccurred after sea storms during two winter seasons, with the formation of an erosionshore about 4 m high over the Pleistocene clastic substratum, whose retrogradationis still taking place and is threatening the structures of a local resort (Fig. 50).3.5.2.4 Hazard affecting lagoonsAnother problem regarding coastlines of great environmental and economicimportance is found in lagoons, marshes, deltas or estuary wetlands. In these areasthe development of aqua-culture activities is in contrast with the need to preservebiotopes of international importance. Wetlands in general are subject to fillingprocesses which are taking place more or less rapidly according to the managementtrends of surrounding territories.In the lagoons of Veneto, in the northern part of the Adriatic Sea, a variation inthe hydraulic regime, with prevalent transportation of fine sediments by the affluentrivers, is favouring the development of eutrophic conditions leading to theoverproduction of biogenic material. Moreover, a further alteration of the ecologicalbalance of these environments as been caused by the intake of waste substances fromhigh-density urban settlements and farming activities. This new tendency has reducedFig. 50. Villasimius coast, "Spiaggia del Riso" after a year from the construction of the new touristharbour. Legend: 1) granites with basic dykes: 2) quartz sands in a highly oxidised silty matrix(Versilian); 3) present sands; a) emerged abrasion shelf: b) transgressive pebble deposit; c) erosionshoreline subject to accelerated retrogression shows some pedogenetic levels; d) original shoreline.

125and in some cases ruined the productivity of these lagoons as food resources.The same problems, with varying levels of gravity, are involving the Adriaticlagoon system of the River Po delta which makes up one of the most significantnatural environment of the Mediterranean.In the Mediterranean morphoclimatic domain the filling up processes affectingcoastal wetlands are often caused by occasional high-water events. In the coastal plainof the Flumendosa River, in south-eastern Sardinia, the inadequacy of the slopes andthe man-induced degradation of the vegetal cover owing to fires, sheep grazing, etc.,produces great quantities of detrital materials. Dismembered slope materials aretherefore loaded up and transported towards the sea in concomitance with catastrophicfloods which periodically occur at the end of every dry season. The detrital masscarried by the river passes through the coastal plain, damaging farming activities andtransport infrastructures and is finally dispersed into the lagoons. In this way adevastating effect on the biological balance in fish-breeding plants is produced,accompanied sometimes by the total destruction of high value food resources.The lagoon systems are goverened by extremely complex equilibria betweenphysical and biological processes. Sometimes interventions of hydraulic engineeringaiming at a rational water exchange with the sea, produce deep changes in thenatural equilibria instead with consequent diffusion of salt water into the environment.This is the case of Cabras lagoons, in centre-western Sardinia, whose fishproductivity used to be among the highest in Europe but has now fallen to extremelylow levels.3.5.2.5 Hazard affecting continental shelvesOn a continental 5/z^//hazard conditions are defined as follows:1) rapid progradation of deltaic apparatuses;2) high sea-floor dynamics of sediments;3) active geodynamics.Moreover, on a continental shelf the impact of human settlements is felt to a greaterextent, such as the dumping of industrial waste and the input of urban sewage.An example of the former can be found in north-eastern Sardinia, where rias coastmorphologies are frequent, i.e., derived from fluvial valleys submerged by the sea.In this area the Olbia ria is located which is occupied in its innermost part, 4 kmfrom its outlet, by an important tourist harbour and industrial port as well as by thecity of Olbia itself. Access is made through a narrow, 100 m wide and 10 m deep,navigable channel. The ria itself was utilised as an anchoring and trade landing placesince the Punic period (sixth century B.C.), whereas in Roman times it was the mostimportant port in Sardinia. At present the ria is affected by accumulation processesof fluvial sediments resulting from the increase of solid load in the Rio Padrongianu,whose delta is placed at the southernmost tip of the inlet. While a small portion ofsediments is taken in load by littoral drift and transported towards the outer mouth,the high content of organic particles from the sewage waters of the city of Olbia andconcentrated in the marine environment amalgamates with most of the fluvialsediments, thus hindering their dispersion. Therefore the filling processes of the ria

126act directly on the access channel to the harbour, causing a serious risk for maritimetraffic and compelling port authorities to undertake continuous, extremely expensivedredging and reclamation operations (Fig. 51).In the Mediterranean marine prairies made up of Phanerophytes {Posidoniaoceanica) are the main element controlling the trophic state of the sea environmentand a fundamental regulation element of the geomorphic processes taking place in theupper continental shelf and submerged beaches. The extension of marine prairiesdepends on the general, climatic-morphological conditions of the environments inwhich they are found and reacts prompdy to global changes. It should be emphasizedthat at present the prairies investigated show critical stability conditions and evensmall actions from the outside can produce rapid retrogradation processes in its lowerand upper limits or widespread degradation. The external man-induced actions arebrought about by mechanical demolition in the case to create anchoring points andby the practice of trawl-net fishing (Fig. 52). Moreover, urban and port settlementsalong the coasts give rise to covering processes produced by the sedimentation ofsuspension particles, whereas chemical degradation is caused by industrial andagricultural products spilled over the territory. The maintenance of optimal quality forthe marine environment is the best way of preserving very important resources forFig. 51. Aerial photograph of the southern shore of Ria di Olbia (north-eastern Sardinia). 1) Progradatingdelta of Rio Padrongianu; 2) dredged canal for access to Olbia's commercial and industrial harbours.

127Fig. 52. Side scan sonar image of the continental shelf of the Gulf of Orosei (centre-eastern Sardinia)showing the damage caused by trawl-net fishing on the Posidonia oceanka marine prairies. Legend: 1)canal filled by sand ripples; 2) furrows due to mechanical erosion; 3) sea-floor profile (modified after Orrii& Ulzega, 1987).Mediterranean countries, regarding both tourism and fishing activities. Among therisk situations connected to the degradation of sea prairies there is the reduction offishing stocks owing to the lack of adequate nurseries, as well as the increase in theextension of submerged beaches, with consequent degradation of the dry beaches usedfor seaside resort activities.At varying depth on Mediterranean continental shelves, rock scarps, whichevolved during the Quaternary glacio-eustatic regressive and transgressive phases intosea cliffs, are often preserved. At the moment of their morphogenesis, these cliffswere subject to coast dynamics which produced rock falls, rotational slides, deepseatedgravitational slope deformations with basal accumulations of both landslidemasses and debris fans. Their submersion with respect to the present sea levelstopped the undermining processes at the foot of the cliffs but did not nullify theirinstability. For example, in the gulf of Asinara in Sardinia at a depth of about 70 mthere is a 20 m high paleocliff, which developed in Miocene calcarenites withmonoclinal attitude. Its front is affected by a succession of rotational slides alternatingwith debris fans (Fig. 53). Another example is found on the shelf in north-westernSardinia, off the coast of Alghero, where at a depth of 80 to 120 m a paleoshore ofstructural origin, with alternating high cliffs and inlets, is present. This landform ismade up of Mesozoic carbonatic rocks and on the walls of the cliffs shear surfaces,open fractures and heaps of unstable blocks are preserved. These structures are allrelated to large rock falls (Fig. 54).

128Fig. 53. Block-diagram of the submerged cliffs of Gulf of Asinara (northern Sardinia). 1) Miocenecalcarenites; 2) coarse clastic sediments and blocks: 3) sandy and silty sediments; F) presumed fault; a)sharp rock edge and detachment crown; b) rotational slide rock body; c) accumulations at the toe of therock edges; d) rock edges buried by fme sediments; e) layer's heads bounded by sharp edges; f) cutsburied by fine sediments (after Ulzega et al., 1986).In these situations of potential risk in conditions of tectonic stability, engineeringprojects, such as the construction of platforms for the exploitation of hydrocarbonsor the laying of submarine pipelines, should start only after carrying out a careful andprecise check of the geomorphological conditions of the sea floor.A different problem is given by paleocliffs in tectonically active areas, asemphasized by the example of the straits of Messina. The sandstones and conglomeratesof the Messina Formation (Middle-Upper Pleistocene) are intersected bymarine abrasion shelf at present dismembered into several portions found at varyingdepths, up to 90 m. The neotectonic movements and the seismogenetic activity keepthe rotational sliding surfaces of the continental shelf edge active. Moreover, thecover of the superficial sediments is affected by gravitational sliding producingdetachment niches at the top and landslide accumulations at the toe. The channelbetween Sicily and the Italian peninsula is affected by the presence of various workssuch as gas and oil pipelines, electric and telephone cables (Fig. 55). Theseengineering works are subject to continuous monitoring because of the highgeomorphological and sedimentological dynamics of the straits of Messina, whereasthe planning and constructing of major communication infrastructures (road andrailway bridges or tunnels) is made extremely complex by the same problems.3.5.2.6 Hazard affecting continental slopesThe passage from continental shelves to deep sea floors usually takes place along an

129Fig. 54. Block-diagram of the buried cliffs of the Alghero coast (north-western Sardinia). 1) Mesozoiclimestones and dolostones; 2) bioclastic sands and gravels: 3) silty sands; a) 75—80 m deep abrasionsurface; b) step-like edges and outmost boundary of buried abrasion shelves; c) closed depression filledby fme sediments; d) fractures; e) mega-ripples fields; f) presumed faults; g) 20-30 m high subverticaledge; h) canyon; i) riverbeds; 1) fan-deltas; m) buried abrasion shelf (after Ulzega & Orrij, 1990).inclined connection surface on which important geomorphological processes occur.On the continental shelf break and slopes the main cause of hazard is given bygravitational instability, related to progradation of sediments on the break, seismicand volcanic activity and the dynamic evolution of canyons.Sediment mobilisation due to gravitational energy, takes the form essentially ofslumpings, turbidity currents and debris flow. The transportation of sediments fromthe slope to the bathyal plains assumes extremely high hazard values especially incorrespondence with tectonically active margins.An example of canyon dynamics in a situation of tectonic stability is offered bythe continental shelf of western Sardinia, deeply cut by the heads of several canyons.Among them, the Gonone canyon shows retrogradation due to regressive erosionwhich leads the head itself to move upstream up to a depth of 50 m, at a distance of200 m from the high sea cliffs of the coast (Fig. 56). The shallow depth of the

1301:25000Fig. 55. Block-diagram of the Strait of Messina, Sicilian side near Mortelle. 1) Poorly cementedsandstones and conglomerates of the Messina Formation (Middle-Upper Pleistocene); 2) cross-beddinglittoral sands (Holocene); 3) shelf's silty sands and sandy silts (Holocene-Present); a) marine abrasionsurfaces disjointed by neotectonic activity: b) gravitational slide surfaces; c) detachment crowns ofsuperficial sediments in boundary zone; d) basal landslide heaps; e) methane pipelines (after Orru et al.,1994).canyon head has allowed its dynamics to be studied and the evolutional process incourse to be defined by means of scuba diving investigations; among thesephenomena the linear movement of the shelf sediments, the block slides of presentbiogenic formations and Pleistocene beach-rocks and the formation of wide slumpingsurfaces are studied. The construction of a submarine pipe for the dumping of urbansewage is now being planned; its outlet will be placed in correspondence with thecanyon head. If on the one hand the active processes of sedimentary dynamics willfavour the disposal of sewage, on the other hand active gravitational sliding is a riskfor the work itself and special foundations and continuous maintenance interventionsare necessary.Another example referring on the other hand to a tectonically active area isoffered by the Tyrrhenian coast of Calabria, where the continental shelf is of suchlimited extent that in some cases the canyon heads reach the proximity of theshoreline. A series of step-like normal faults affect the whole continental marginfavouring the formation of sliding surfaces. In these morpho-structural conditions agreat industrial harbour is being constructed whose entrance is placed exactly betweenthe two heads of the Gioia Tauro Canyon. At the moment of its construction, thematerials resulting from the digging of the port basin, about 5.5 million cubic metres,were thrown into the sea directly on the canyon's margin. On June 12, 1977 at

131Fig. 56. Block-diagram of the Gonone canyon (centre-eastern Sardinia). 1) Mesozoic limestones anddolostones; 2) stratified sediments (Miocene-Pliocene:'); 3) basalts (Quaternary); 4) deltaic and lagoon siltswith peat (Upper Pleistocene); 5) paleoriver deposits; 6) sandstones and beach conglomerates (UpperPleistocene); 7) organogenous silty sands (Holocene); 8) littoral sands (Holocene); a) canyon linear cuts;b) heads subject to erosion with cropping out of bedrock; c) edge progradation; d) slumpings; e) basalticplateau with emission centre; f) paleodelta; g) beach-rocks; h) paleolagoons; i) paleocliffs with structuralcontrol; 1) lithothamnos plain; m) Posidonia oceanica sea-prairie; n) active sea cliff with Pleistocene andHolocene caves and breaker furrows; o) delta; p) lagoon; u) submarine pipeline. Detail of the canyon'shead; 1) basement; 2) red algae bioconstructions; 3) ripple-mark sands; 4) silts; a) sea rocks; b) biogenicreef subject to landsliding; c) gravitational sliding furrows of organogenous coarse sediments; d)gravitational sliding of fine sediments, slumpings (after Orrij & Ulzega. 1987).7:20 h, a submarine landslide was triggered in the dumping area whose current ofturbidity, travelling at a speed of 15 17 km/h. caused at 8:12 h the rupture of a cableat a depth of about 600 m. At the same time, on the surface a lowering of the sealevel by about 2 m first occurred, soon followed by a 5 m high wave which hit theharbour structures and the coast thus causing the demolition of one of the quays andother widespread serious damage (Fig. 57). The subsequent study of the Gioia Taurocanyon, carried out by scuba divers and submarine explorations along its slopes andaxis up to a depth of 1,000 m, clearly showed that the event could be foreseen, dueto a situation of great geomorphological risk. A similar event took place on October16, 1979 in Nice where the waste materials derived from the extension works of the

132Fig. 57. Gioia Tauro canyon (southern Calabria), a) Schematic topographic map of the canyon showingits two heads near the piers off the Gioia Tauro industrial harbour; b) longitudinal profile of the canyonshowing the flow time of the turbidity current generated by the landslide (after Colantoni et al., 1992).airport were dumped into the sea at the head of the Var-canyon.Among marginal areas, in the continental slope geomorphological dynamics isnoticeably reduced owing to the limited availability of sediments and the decrease ofslope gradients and, therefore, of gravitational energy. In any case, at the depthspertaining to these environments, 200—2,000 m, works and activities of economicinterest are rare.Fig. 58. Block-diagram of the western margin of the Gulf of Taranto (north-eastern Calabria). 1)Submarine fan of the R. Trionto with linear flow channels along the whole scarp: 2) submarine fan of theR. Crati with top flow channels and basal mass transportation lobes; 3) scarp furrows showingretrogressive heads cutting through the submerged beach.

133

134Nevertheless, situations of hazard can be determined in particular conditions, forexample in tectonically active areas with margins in compression, where a verynarrow margin with nearly nonexistent shelf corresponds to the rapid uplift of the drylands.A significant example of geomorphological evolution of this type is observedalong the southern margin of the Gulf of Taranto, in the Ionian Sea: whereneotectonics has produced a great increase of energy in the slopes of the emergedreliefs, these give way without interruptions to the continental slope, with ananomalous accumulation of materials in correspondence with the coast, which giveorigin to complex sedimentary bodies in conditions of instability along the slope.Migration of the sediments towards the deep sea floor occur by means of linearmovements in cone-shaped structures, the formation of lobes in prodeltaic environment,fan-delta or directly on the upper slope, where the narrowness of the shelfhinders littoral drift. In these conditions, along the whole margin in correspondencewith the heads of the inflow channels, retrogradation niches are formed which directlyaffect the submerged beach: this creates situations of risk, first of all for maritimestructures but it can also cause sudden withdrawal of the shoreline, with hazard forthe roads running along the coast and for seaside resorts (Fig. 58).Another example of continental margin characterised by an important geodynamicactivity is offered by the Hellenian arc. The activity in this case consists of highFig. 59. Channel of Sicily, about 20 nautic miles north of Scherki shoal. Side scan sonar image showingthe sea floor at a depth of-400 m; (a) sand ripples; pipeline subjected to both burying and underminingprocesses: the darkest echoes (b) represent rock block heaps (c) lain down in order to stabilise thepipeline.

135seismicity, with shelf uplift and slope instability. Moreover, active faults affect poorlycohesive evaporitic rocks, situated in the bathyal plain and at the base of thecontinental slopes. Owing to these contributory causes successive landslides triggeredalong the Corinth slope caused the repeated rupture of underwater electric andtelephone cables.In morphological high places channelised in correspondence with straits, strongcurrents are usually created, due to the compression of the flux lines of large watermasses; this phenomenon takes place with a preferential direction and triggers tractivecurrents flowing with a velocity of some metres per second on the sea floor. Thedisplacement of sediments gives rise to parabolic dunes with high translation velocity.In the western Mediterranean, this phenomenon was observed in the Straits ofMessina and in the Channel of Sicily. The latter is a body of water stretching fromCape Bon in Tunisia to Cape Feto in southern Sicily. The morphology of the channelincludes Adventure Shoal to the north and Scherki Shoal to the south, in turnseparated by an axial zone structured by a horst-graben system forming ridges andparallel channels with a NW-SE direction. On the bottom of the channels intensedynamic processes affect the coarser sediments which migrate towards the PantelleriaBasin to the south in the shape of parabolic dunes up to 20 m long and 3 m high.Along this path, three parallel methane pipelines which are the main energy linkbetween North Africa and Europe were constructed. The movement of parabolicdunes can cause the undermining at the base of the pipelines which, in order toprotect them, are weighed down with a cover of rock blocks and by regular periodicalinspections (Fig. 59).3.6 Glacial and periglacial hazard**by Alberto CARTON3.6.1 IntroductionThe situations of environmental risk in high mountain areas are mainly linked to thepresence of ice and snow masses. Moreover, there are other phenomena thatprogressively lead towards gravitational movements in a strict sense; they are mainlydue to the action of ice, snow and melt water.Since the areas where these phenomena take place are often remote and with avery scarce human presence, the resulting risk is often underestimated. In fact, theconsequences often affect territories located even at noticeable distances from theplace where a certain phenomenon has occurred. In the particular case of an alpineenvironment, the effects can be felt as far as the valley floor. As a consequence, ina period when mountain exploitation for sport and tourism purposes is very intenseboth in summer and winter, the hazard no longer concerns the single user but ratherpermanent anthropic structures or small and big sites alike, which are often very busywith people, although only seasonally.The hazard rate of certain phenomena is in certain cases very high owing to their

136suddenness which is accompanied by a poorly defined or totally lacking series ofpremonitory signs linked to several variables and not always completely known oradequately taken into account.The prevention of these types of processes is moreover under-evaluated sincewithin the field of natural hazard phenomena those regarding the presence of snow,and even more of ice masses, certainly do not represent a high percentage. Finally,in the present phase of retreat or immobility of the glacial fronts, also ice dynamicsseems to be underestimated or neglected by most people, apart from specialists andsome other frequent visitors of the mountains. On the contrary, one should considerthat climatic changes occurring even in a short time (e.g., little Ice Age) can producedeep variations in the ice mass which in turn could affect recently developed areasor predispose future hazard situations.Hereafter, the hazard phenomena (Fig. 60) that can be found in a mountainenvironment are listed:— ice rock avalanches;— supraglacial debris fall/slide outside the lateral moraine;— ice fall from snout of glaciers (ice avalanches);— rapid advance of snout of glaciers (surges);— emptying of internal water-pocket;— emptying of proglacial lake;— emptying of ice-dammed lake;— debris flows caused by bursts of dammed ice;Fig. 60. Typical example of periglacial hazard: in the foreground the destructive and accumulation effectsof an avalanche; in the background an avalanche cone (photo M. Panizza, Caucasus, June 1974).

— debris flows caused by bursts of ice-marginal lakes;— debris flows resulting from bursts of moraine dammed lakes;— debris flows resulting from bursts of subglacial and englacial water pockets;— high water events connected with rapid glacier ice melting;— lahars;— hazards caused by mountain climbing activities;— mass falls due to glaciopressure;— avalanches;— advance of rock glaciers;— debris flows caused by short and intense precipitations on scattered glacialdeposits or by talus deposits.Before considering the series of phenomena that take place in the mountainenvironment, the formation of debris flows should be emphasized in particular, sincethey are a recurrent phenomenon among those connected with glacial dynamics. Theirformation is mainly determined by sudden releases of large amounts of melt wateras well as by the abundance of unconsoHdated sediments which are usually foundnear the unstable glacier margins in the form of thick moraine ridges or as scatteredglacial deposits or, more generally, as ice-contact debris.Moreover, the constant retreat of the glacial fronts, starting from the middle oflast century (which coincided with the maximum Holocenic expansion), hasuncovered very vast surfaces, at present covered by large amounts of detritus not yetfixed by the vegetation and often lying on polished rocks. On the same surfaces ahydrographical network deriving from a glacier is found, characterised by extremelyvariable and unforeseeable flow-rates and capable of loading remarkable quantitiesof loose glacigenic sediments.As regards the waters more specifically, it should be remembered that theparticular land surface arrangement (high relief energy, deep valleys, etc.) emphasizes,from the hydraulic standpoint, the effects of surface running waters,conferring them with high energy: their flow is often confined in narrow, steep anduneven spaces (gorges, troughs, canyons). In cases when glaciers release suddenamounts of water, some torrents are compelled to run in valleys which are inadequatewith their new occasional flow; as a consequence, an anomalous raising of their leveltakes place with the depositing of various types of debris located on slope portionsusually untouched by the flow of watercourses.3.6.2 Ice-rock avalanchesIn some morphological and structural situations, ice and rock avalanches involvinglarge volumes of material can occur. This phenomenon affects at first only portionsof rocks that by sliding drag along also ice masses in their movement (Fig. 61). Theso-formed melange is extremely mobile and can run very long stretches. The presenceof ice, both in the form of blocks and/or melt water, modifies the mechanicalbehaviour of the landslide body by reducing the shear strength angle, making it veryfluid and providing a "lubricated" sliding surface. More seldom the phenomenon can137

138Fig. 61. Schematic example of supraglacial rock fall outside the lateral moraine.take place when a suspended glacier lies on fractured, easily degraded rock as a resultof the infiltration of large amounts of water repeatedly turning into the solid state.Even seismic events can trigger ice-rock avalanches.The consequences of such a phenomenon can be both of direct and indirecttype. An ice-rock avalanche can directly affect works connected with man'sactivities or create barriers to the hydrographical network with the consequentformation of temporary impoundment areas. In the latter case the heap's morphologicalfeatures and dimensions can change with time, following the melting ofthe entrapped ice: variations will thus be a function of the amount of ice involved inthe fall.The development times of the phenomenon are extremely short and prediction isalmost impossible. Only in some cases can the starting of isolated rock fallsforeshadow the event. Usually the rock portions affected by this kind of disarrangementare located in inaccessible places or at least in areas which are not normallyfrequented and are therefore not normally kept under direct observation. When aslope's proneness to movement is detected, it will be possible to set up a traditionalmonitoring system on the unstable rock mass if the consequences are assessed asnegative for human activities.Ice-rock avalanches of large proportions are reported in the specific bibliography

139regarding Peru: among catastrophes of this kind perhaps they were the mostdisastrous. From the top of Mount Huascaran in 1962 a portion of the ice capdetached (3.5 million cubic metres). A second avalanche of about 300,000 m\detached from just below, followed the previous one. The great volume of icedragged along a large quantity of rock and subsequently hit and removed a portionof a glacier. Eight villages were submerged and destroyed. Following an earthquakein 1970 an ice-rock avalanche was formed from the same Mount Huascaran; thetowns of Ranrahirca and Jungay were devastated.Also in the Caucasus several cases of ice-rock avalanches were recorded. At thetoe of Kazbek, from the Defdoraki glacier, rocks, mud and ice fell into the underlyingvalley in 1766, 1785, 1808, 1817, 1832. In the central Caucasus, the valley of GuenalDom was devastated in July 1902 by two ice-rock avalanches coming from a glacialcirque bordered by the Giumaraykhkn, Kazbek, Marly Knokh and Fombal Fziti peaks.In the Alps, on the Simplon Pass, in 1901 on the flank of the Fletschorn a largevolume of stones was detached and fell on the Rossbode glacier thus forming agigantic avalanche rated at 2^3 million cubic metres.In literature other cases of ice-rock avalanches are described on the Italian sideof Mont Blanc in Val d'Aoste (Val Ferret and Val Veny) in 1717, 1728 and 1920.In Switzerland in the Valais in 1714 and 1749 a vast amount of rock below theGlacier de Diablerets slipped perhaps owing to the glacier's melt water percolatingwithin the rock fissures.3.6.3 Supraglacial debris fall/slide outside the lateral moraineThis phenomenon can take place during a glacier's accretional stage with aprevalently vertical development. At times the ice thickness increase can reach orovercome the height of the lateral/frontal moraine. The event takes place preferentiallyin the glaciers whose top is covered with abundant supraglacial debris (blackglacier)or when large boulders which have fallen on the glaciers are conveyedtowards zones more favourable topographically to this type of phenomenon. Thethickness increase of a glacier tongue is not necessarily determined by an expansionphase, especially when glaciers with abundant floating moraine are considered. In thelatter, in fact, ablation is strongly inhibited by the debris cover and in difficultsituations of frontal and superficial ''disposal" the mass can react by swelling up.Once it has reached the top of the moraine, the coarser detritus can slide outwardlyas far as the scarp's toe (Fig. 62).The effects produced by this kind of event are normally of small entity and fallin the category of risk case histories only if they directly involve anthropic works(usually roads and paths).The phenomenon occurs suddenly when it actually takes place but its preparationdevelops slowly and is easily controlled. Usually only modest amounts of debris ormore often isolated boulders are involved. Premonitory signs are given by a series ofsmall slides along the morainic bank's outer scarp or by the proximity of largeboulders to the glacier margins. When the debris' coarser fraction shows instability,

140as-;'^

locks from the summit of the lateral moraine onto the road underneath, along a 200-300 m long front (Dutto & Mortara, 1992).3.6.4 Ice fall from snout of glaciers (ice avalanches)141The fall of great portions of ice is typical of those glacial tongues showing asuspended front (slope gradient over 30"", Eisbacher & Clague, 1984) or lying onrocky bedrocks showing particular morphological features. The fall of the front cancause an ice avalanche owing to both a net detachment of the tongue's foremost partand a slide or topple of seracs (Fig. 63). The detachment of the glacier's front takesplace when the weight of the portion that is going to slide overcomes the sum of thefrictional and cohesion forces at the bottom with the rest of the mass. The detachmentusually occurs in correspondence with a crevasse and can be caused by a thinning ofthe ice mass due to the effect of traction towards the lower part of the valley. Thisis caused by a net difference between the glacier's advancing velocity and thatassumed by the frontal part; the latter being imposed by the weight of the masslocated along the steepest stretch. Other times the phenomenon occurs during an icefall characterised by crevasses going nearly as deep as the bed rock, thus reducingthe connection surfaces with the rest of the mass. This type of event can be favouredand regulated not only by the force of gravity but also by the air temperature which,following the ice melting, can form water films at the bottom of the glacier (Heim,1895) acting as a lubricant with consequent velocity increase and friction decrease.Other rare cases of ice avalanche detachments can take place in those glacial bodieslying isolated and suspended in niches located on steep slopes. If the ice is collectedwithin a concavity, in particular climatic conditions, a water layer can form betweenrock and ice, capable of detaching the ice mass from the bedrock and perhapsdiminishing the ice weight on account of a hydrostatic thrust. Even earthquakes cancause the fall of glacial fronts or ice falls.Fig. 63. Schematic example of ice avalanches.

142Often if the ice volumes or the quantity of seracs involved in the fall areconsiderable, an ice-block avalanche can form which is sometimes mixed with debriscollected during the movement (Alean, 1985). The distance run by the ice mass canbe very long, since the slide takes place between media having a low frictionalcoefficient (ice on ice or ice on rock).Premonitory signs can be: an increase of ice fall activity at the glacier's toe, withrepeated and frequent detachments, observation of sudden movements of large icemonoliths or sudden openings of crevasses. In situations of potential or actual hazard,the zones can be monitored by means of photogrammetry techniques or remotesystematic control by using benchmarks located on points presumably involved in themovement. Moreover, wherever possible, cables fixed to the ice and connected tostrain meters can be used, in order to assess the extent of the opening of crevassesor the ice mass dilation. This second type of control implies a series of logisticalproblems since the anchoring points of the steel cables and the topographic signs areplaced in positions which are often inaccessible and/or covered with snow for severalmonths a year. Moreover, traditional topographic control implies other problems,often linked to the distance of the fixed stations (necessarily placed on oppositeslopes in a panoramic view) and the maintenance of the sights' verticality. Probablythe application of the G.P.S. could give a useful contribution by systematicallymeasuring the position of the prefixed benchmarks and in assessing the thicknessvariation of the ice body.The damage produced can be of different extent. If the ice-avalanche stops at thetoe or near the glacier, where human settlements or works are not usually present,then the damage can be limited. In this case the subject involved will be themountain-climber, and the phenomenon will fall within the case histories of mountainaccidents. On the contrary, the entity of the damage can be relevant if within theradius of action of these phenomena ski pistes or ski-lifts are present. On the otherhand, if the distances run are noticeable, the mass can affect large valley portions andstretch as far as the location of human settlements or involve areas of high dailyfrequency (the summer months and the warmest hours are usually the most favourableperiods). The phenomenon can interfere with the hydrographic network only for shortperiods; the possible barriers will progressively lose volume with time as a result ofice melting.One of the events of this type that most struck public opinion took place on 30August 1965 when a large portion of the Allain glacier's front crashed into the hutsand the service road of the Mattmark building yard. The building yard had beenplaced in that area for the construction of a dam which, among other purposes, shouldhave defended the valley from another hazard connected with the presence of theglacier, i.e., to avoid the frequent and catastrophic depletions of lake Mattmark (aglacial barrier lake with intermittent regime linked to the glacier's advancements).The tragedy created a stir not only for the number of casualties but for the region inwhich it happened which, by tradition, has taken great care regarding this kind ofproblem.One of the worst tragedies in the history of alpinism happened in 1990, again as

143a result of a serac detached from a glacial front. In the Pamir range, at the borderbetween Tadzikistan (former Soviet Union) and China, an earthquake caused an icefallwhich triggered a huge avalanche.In September 1895 in the Bernese Oberland a portion of the Altels ice tongue (4miUion m^) broke at 3,100 m and fell to the Gemmi valley floor. During the previoussummer a vast crevasse had formed in the stretch subsequently affected by thedetachment.Miraculously unscathed was the village of Randa in 1973 (Zermatt valley, Valais).500,000 m^ of ice detached from the front of the Bis glacier, fortunately in severalsequences. Prior to this, however, this glacier had created several problems.In 1977 on Mont Blanc about 200 people in the village of La Tour werethreatened by an ice-fall from the Tour glacier. In 1949, from the same glacier, some450,000 m^ of ice had detached.The village of Eggen was totally transferred following its destruction in 1957 dueto the fall of an ice mass from the Hochmatten glacier, located on the western sideof Breihorn, on the Simplon massif.3.6.5 Rapid advance of glacier snouts (surges of glaciers)Some catastrophes finding their origin in glacier phenomena are also linked toexceptional, sudden and rapid advances of glaciers' snouts, also called surges ofglaciers. Such phenomena have been observed in the North American glaciers inGreenland, in Alaska, in Antarctica, in Karakorum and in the Italian Alps. Evidenceof ancient advances have been recorded also in the Swiss Alps.This mechanism has not been completely understood, although it seems to dependon the dynamic behaviour of the glacier rather than on strictly climatic causes.Various authors have taken interest in this subject: Embleton, Flint, Kasser, King,Paterson, Post, Robin, Sharp. According to some of these researchers, the phenomenonis connected with the glacier's mass balance (Kasser, 1970, in Adrian, 1975),but this would not be sufficient to explain the velocity of the mechanism. Robin(1969, in Adrian, 1975) proposed three causes, actually linked to the glacier'sdynamics: 1) stress instabilities; 2) temperature instabilities; and 3) bed-frictioninstabilities.Stress instabilities in a layer of ice can be caused by recrystallisation of individualportions of the glacier under strain; the stress concentrations can propagate as wavesand can thereby produce unusually high rates of flows (Jonas & Mulles, 1969; Robin,1969; Robin & Barnes, 1969; Palmer & Nye, 1972, in Adrian, 1975). Also thewarming up of cold glaciers can produce a rapid and sudden advance (Lliboutry,1969, in Adrian, 1975). Nevertheless, temperature instabilities are not considered asa primary cause, since the phenomenon has been observed at the same time intemperate glaciers. Probably the main cause is given by a sudden change of thefriction conditions at the base of the glacier. A sudden decrease in the bed-frictioncan in fact be produced when the thickness of a water layer at the bottom of theglacier exceeds the size of the bed obstacles or following the detachment (super-

144cavitation) of ice (Weertman, 1962; 1969; Lliboutry, 1964, in Adrian, 1975).Campbell & Rasmunsen (1969, in Adrian, 1975) demonstrated that a friction decreaseof only 5% is sufficient to cause a surge.In some cases are the advance velocities really exceptional: Embleton & King(1971) recorded advances of some 350 m per day, Post (1960, in Adrian, 1975)measured a movement of 6.5 km in no more than 9 months for an Alaskan glacier.More generally, according to Patterson (1969, in Adrian, 1975), during a surge aglacier can move with a velocity up to 100 times greater than its normal one.The rapid advance of a glacier snout causes both direct and indirect types ofhazard. The cases where an advancing glacier snout occupies territories whereanthropic infrastructures are present fall within the first type. Those where a surgetriggers other natural phenomena such as ice mass instability or damming ofconfluent valleys, belong to the second type of hazard. For example, it seems that theHuascaran ice-avalanche of 1962 (Morales, 1966) and the Mattmark accident(Eisbacher & Clague, 1984; Brockamp et al., 1967) were caused by glacial surges.The still scanty knowledge of the triggering causes of surges as well as thevarious theories so far produced show that the problem has not been completelysolved. For this reason it is extremely difficult to foresee and/or monitor events ofthis type. Considering that each individual glacier tends to assume with time the sameattitudes, at present the only reliable way to hypothesize future events consists inanalysing their behaviour in the past, by means of historical analyses and fieldsurveys (geological glacial studies).Case histories related to this phenomenon are numerous and scattered all over theworld. Since the mechanism is not well-known, sometimes the event is ascribed toother causes. Besides the cases quoted above, another surge phenomenon is worthyof mention since it was a very spectacular case for the Italian Alps, although it didnot have direct consequences for the territory: the advance of the Solda glacier snout(Ortles-Cevedale Group) which underwent an advance of over 1,200 m (Desio, 1967)in only one year (1817-1818).3.6.6 Emptying of internal water-pockets, proglacial lakes and ice-dammed lakesSome of the glaciers' melt waters fill superficial endoglacial or subglacial cavities,forming lakes or water pockets which owing to different causes can quickly releaselarge amounts of water. Water reservoirs are frequent at the margins of glacialtongues in correspondence with depressions between ice and rock, between ice andmoraine ridges and between ice and ice (Fig. 64). Other basins can be formedfollowing the damming of a valley by a glacial tongue. Water pockets are alsopresent within the glaciers and probably correspond to the most hazardous situationssince their existence is not known beforehand. Other small bodies of water can befound between ancient end moraines or be formed by the damming of a valley by alateral moraine. The latter cases, though, seem to show a low hazard degree sincethey are not directly involved in glacial dynamics.It is obvious that the most important hazard phenomena connected with the

145Fig. 64. Schematic example of internal water-pockets.depletion of water reservoirs of glacial origin almost exclusively affect areas occupiedby temperate glaciers undergoing intense melting with a runoff occurring both at thesurface, at some depth and at the bottom of the glacier.The water pockets forming inside a glacier or at bottom depressions can evolvein different ways. The former are "water bubbles" migrating according to themovements assumed by the glacier which will exist until the surface of the cavitywithin which they originated is breached. This can occur as a result of the formationof a new outlet due to a glacier's physicodynamic variations (crossing of a crevassearea, collapse of ice portions supporting the pocket, etc.) or a contact with a glacier'smargin. The latter can be depleted owing to the removal of temporary obstacles inthe subglacial flow. In any case, the water volumes made available through endo- andsubglacial runoff vents (Jackson, 1979) will emerge at the glacier's margins, usuallyin extremely short times.The depletion of epiglacial basins is also linked to the glacier's physicodynamicvariations, resulting from the modification of the supporting topographical surface orthe opening of endoglacial runoff ways (crevasses). In the first case the water runoffwill be prevalently superficial.

146The other ponds placed at the margins of the glacial tongues (Fig. 65), especiallythose located in depressions between ice and morainic ridges, or outside them, cansuddenly release their water as a result of a dam's failure or cuts in the moraine. Inthe first case the cause can be the pressure exerted by the water on the ridge, whichcauses a syphoning or a settlement (Costa, 1988), or a partial failure in correspondencewith ice-cored points (Haeberli & Epifani, 1986). In the second case a mildsaddle in the summit profile of a containment ridge, in concomitance with a suddenraising of the pond's water level (snow and ice melting, intense rainfall, etc.), can actas an overflow and eventually become deeper on account of linear erosion. In thesecases, as well as the highwater wave, a large quantity of material directly removedfrom the ridge itself is mobilised from the onset, thus giving way to a debris flow.When the basin is formed due to damming by a glacial tongue, the water releasecan occur owing to a failure or settlement of the tongue or its retreat (Clague &Mathews, 1973). Typical of the latter phenomenon is a repetitivity normally linkedto ice fluctuations (Vivian, 1975; Tokmagambetow et al., 1980).The sudden release of large volumes of water following the opening of an outletgives origin to phenomena of noticeable torrent activity, ranging from disastrousfloods to the mobilisation and transport of considerable amounts of debris (debrisflows); the latter is usually abundant on the spot, in the morainic ridges or on widesurfaces recently freed from the glaciers following the progressive and continuous iceretreat since the middle of the nineteenth century. The entity of the effects willdepend on the amount of water released, the release time, the sloping of the channelFig. 65. Schematic example of proglacial lake at the margins of the glacial tongues.

which collects the running waters and its capacity to take the loose debris. In specificliterature these events are named with such terms as debacle (French), glacial burst(English), jokulhlaup (Icelandic).As regards subglacial or endoglacial water pockets, it is practically impossible toforesee their existence and consequently to prevent their effects. If studies of glacialgeology show the tendency of a certain glacier to have this type of event, it might beworth trying to identify the existence of these water basins by means of geophysicalmethods (for example, georadar, radio-echo-sounding, etc.). These investigations,though, are usually expensive and impracticable and seldom produce clearlyinterpretable results. In any case, if the location of a cavity is known, it could bedrained by a tunnel. Other premonitory signs can be looked for, such as anomalouslowering of the lake's level, increase of flow-rate and turbidity in the pro-glacialtorrent, formation of new springs and little streams outside the morainic ridges.Experience teaches us that in these cases rather than forecasting, the best remedialmeasure would be prevention, which can be carried out by means of appropriatemodelling and stabilisation of the pro-glacial streams' riverbeds and protective worksagainst the occurrence of debris flows.Prevention from the damage caused by natural water reservoirs located withindepressions between ice and rock, or between ice and morainic ridges, or between iceand ice, due to damming by a glacier tongue, can still be carried out effectively whenthe accumulated water volume is not excessive. Tunnels or canals may be dugthrough the ice, rock or debris in order to control the level of the dammed lake. Ifthese measures are not appliable on account of logistic difficulties, it will benecessary to construct flow-control weirs and debris containment dams downstreamof the lake.In some cases, in order to avoid the formation of large impoundments, it is usefulto prepare a deep and stable cut, properly coated with brickwork, in order to avoidthe collapse of detritus and removal of material which would certainly trigger debrisflows in concomitance with highwater conditions. In order to identify and preventpossible settlements or siphoning in morainic dams with ice-cores, their presencecould be ascertained by means of thermic flow analysis in the ground with BTSmeasurements (Bottom Temperatures of the winter Snow cover).The realisation times are extremely rapid, since a dam's failure (be it of ice ordebris alike) takes place in short times and at unexpected moments. Only when alarmsystems are installed is it possible in most cases to avoid the loss of human lives.In the high mountain environment, this type of phenomenon is one of the mostfrequent and several examples have been recorded in the specific bibliography. Casesof flooding linked to glacial breaches and debris flows determined by the collapse ofice dams have been described in nearly all the temperate glacialised regions of theworld: in the Himalayas, in the Karakorum, in the Caucasus, in Norway, in the Alps,in the Peruvian Andes (Cordillera Blanca and Hua Yuashe), in the western part ofNorth America, in Alaska and in Iceland (Clague & Rampton, 1982; Helbing, 1940;Kerr, 1934; Liss, 1970; Mason, 1929, 1935; Mathews, 1965; Post & Mayo, 1976;Stone, 1963; Thorarisson, 1939; Young, 1980).147

148Some cases are particularly worthy of note, such as the disastrous event that tookplace on March 13, 1941 in the Cordillera Blanca owing to an earthquake whichcaused the sudden depletion of two glacial lakes and triggered a debris flow whichdestroyed part of the town of Huaras and killed thousands of peoples.In the Argentinian Andes, in the Juncal group, (near Mendoza) the Nevado glacierdammed a valley, forming a lake that twenty years later (January 1934) was suddenlydepleted.In the Karakorum the Shyok glacier dammed the valley fed by the longest glacierof the chain, the Shiachen (75 km). The lakes thus formed were extremely large andchronicles reported floods connected with them in 1835, 1839, 1842 and 1927.Also the disasters which occurred several times in numerous Alpine valleysshould be mentioned. On the Italian Alps the Santa Margherita lake, repeatedlydammed by the Ruitor glacier, was repeatedly depleted since the second half of thefifteenth century. At the end of the XIX century the lake dammed by the Tongue ofthe Cevedale glacier was suddenly depleted through a tunnel in the ice. In 1979 onMt. Rosa the Locce lake was depleted and gave origin to a debris flow whichdestroyed a chairlift. In Val de Bagnes (Martigny, Valais, Switzerland) a vast iceavalanchefan obstructed the course of the River Dranse and as a consequence abarrier-lake was formed. In the Otz valley, in the Tyrolean Alps, from 1600 until1890 — during the Little Ice Age — barrier-lakes linked to the numerous glacieradvances were formed over 12 times: several jokulhlaup and ice floods were causedfollowing these valley obstructions. Large-sized debris flows were formed from theMattmark lake (Saas valley, Valais, Switzerland), once again dammed by a glacier'stongue and its moraines. In the Tete Rousse Glacier (Arve valley. Haute Savoie,France), a water pocket was suddenly depleted in 1892, thus freeing about 200,000m^ of water and carrying ice and debris downhill. Some of these events, quiteremarkable and recurring in past centuries, have at present reduced or exhausted theirhazard, on account of the noticeable retreat of several glaciers after the Little Ice Age.In other cases, effective interventions have definitely averted the danger (Welchner,1773; Stotter, 1846; Richter, 1892; Finsterwalder, 1897; Liestol, 1956; Hoinkes, 1969,1972; RothUsberger & Allen, 1970; Rothlisberger, 1974, 1979; Nijasov, 1975;Lichtenhahn, 1979; Bachman, 1984; Eisbacher & Clague, 1984).3.6.7 Highwater events on the valley floor connected with the presence of glaciersIn the valleys of catchment basins where numerous glaciers are present, particularmeteorological events, especially of the thermal type, can contribute to increasingexceptional highwater phenomena. At present it seems that few data or specificstudies on this topic are available, although some significant events occurring duringrecent years show the decisive role played by glacial masses (Rey & Dayer, 1990).A sudden temperature increase causes a raising of the freezing level at highaltitudes. It follows that if the areas affected by the phenomenon are occupied byglaciers, vast ice portions usually placed above the snow limit, would be found in theablation zone. Moreover, precipitation which at these altitudes is normally snowfall,

149turn nearly exclusively into rainfall, with consequent rillwash and accelerated meltingphenomena.The release of large volumes of melt water in short times is a consequence ofevents of this type. The increased water availability will then feed the mainwatercourses which will show flow-rate values well exceeding the seasonal averages.Unfortunately nothing can be done to avoid such events: at the most the populationcan be alerted and preventive measures can be taken by means of monitoring thehigh-altitude temperatures and comparing them to the average seasonal trends.An example of this could be the disastrous flood of 1987 in Valtellina (Smiraglia,1987a,b) and also in the higher Val d'Ossola, Northern Italy. During the days of theflood, the temperature values recorded at the stations located at higher altitudes(2,100-2,350 m a.s.l.) were superior to OX. This fact led to a raising of the 0°Cisothermal line to around 3,400 m. Since the main glaciers in Valtellina have theirfronts at altitudes of 2,200—2,500 m, an intense and rapid melting of the winter snowtook place in most of them, thus reducing the drainage basins and depleting the snowaccumulated over several years and perhaps the ice itself.3.6.8 LaharsAlso the rare and yet occurring combination between glaciers and volcanoes can bean element of hazard in mountainous areas. In active volcanoes, whose summit isabove the snow limit or is covered by a snow cap, the occurrence of mud flowscaused by the sudden melting of snow and ice in direct contact with incandescentlavas is quite possible.These flows, called lahars, can interfere with the hydric network and obstructriverbeds or go as far as developed areas. The mobility of these events is high sincea vast amount of fine and cohesionless pyroclastic material suspended in the meltwater is removed.The occurrence of such a phenomenon can only be foreseen on the basis ofvolcanic activity monitoring. In hazardous situations defence works could be planned,although they are difficult to carry out since the event as well as the volume ofmaterial involved are unforeseeable data.The most recent example of this phenomenon took place in 1985 in theColombian Andes. On the Nevado El Ruiz volcano (5,400 m a.s.l.), whose top wascovered by an ice cap, melting and mobilisation of ice and snow followed a smalleruption, with the formation of some lahars, the largest of which destroyed the cityof Armero, claiming 20,000 lives (see chapter 3.8).3.6.9 Hazards derived from mountain climbingA final kind of hazard, although limited and involving only mountain climbers, isderived from the instability shown in some occasions by the ice surface. Alpinistliterature quotes innumerable cases of situations with often tragic outcome, when thecollapse of an ice bridge, the opening of a crevasse hidden by snow or the failure of

150a snow ledge caused the loss of human Hves. Only prudence, experience andcompliance with the basic rules of rock and ice climbing can prevent and reduce thistype of hazard. Another recent activity linked to the presence of glaciers is given bythe practice of summer skiing. Also in this case a strict compliance with the rules setout by the public boards in charge can prevent accidents, considering also that in thelast few years a thinning of glacial masses has taken place as a result of the raisingof the freezing level. As a consequence, many crevasses have formed, together withan increase of the morainic cover and a reduction of utilizable areas.3.6.10 Mass falls owing to confluence glaciopressureIn case histories, also the phenomena derived from slope instability (usuallyconsisting in mass movements such as falls) accompanying the maximum glacierretreat can be mentioned. In the Dolomite region some landslides which took placein the Late Glacial and Post-Glacial were observed; they are characterised by failuresurfaces along slopes at the outlet of valley narrows, upstream of which there is aconfluence of two or more valleys which once were occupied by glaciers (Fig. 66):they were triggered by a tensional discharge following the loss of pressure previouslyexerted on the rocky slopes by two or more glaciers merging in a valley narrow(Panizza, 1973). Even if the fall of large slope portions can directly affect humansettlements or obstruct a whole valley, with the negative resulting consequences, theextremely high hazard degree assumed by this type of phenomenon is purelytheoretical. Indeed, the long time span from the withdrawal of the glacial network tothe present (some 12,000 years) has produced nearly total exhaustion of these events.3.6.11 Assessment of the hazard derived from the presence of ice massesRelying on more or less accurate case histories, some authors have tried toparameterize some aspects of the hazard phenomena derived from the presence of icemasses by identifying their types, the ways they are triggered, their development andpropagation, in order to set out forecast and prevention models (Haeberli et al., 1989;Laenen et al., 1987; Church, 1988; Dutto & Mortara, 1993). The parameters takeninto account for this kind of analysis are usually the development times which eachevent can assume, the propagation distances and the volumes of the materialsinvolved. From an analysis carried out on a certain number of cases (about 90)occurring in the Italian Alps, the following data have emerged (Dutto & Mortara,1993).Falls of glacial fronts and landslides of ice and rock are the events that developin very short times: from a few seconds to several minutes. The depletion ofendoglacial lakes requires times ranging from minutes to hour, whilst for barrier-lakesand proglacial lakes times of a few hours to several days are necessary. The advancesof glacial fronts and the debris falls from the glacier's margins require much longerperiods (months to years).On the contrary, the propagation distances of instability phenomena are maximum

151I ^2405Fig. 66. Late and Post Glacial landslides in the Cortina d'Ampezzo area (Dolomites, Italy) due toconfluence glaciopressure in valley narrows (arrows show valleys once occupied by glaciers) (modifiedafter Panizza, 1973).for the depletion of barrier-lakes and proglacial lakes, followed by mass movementsinvolving ice, depletion of endoglacial lakes, advances, falls of the fronts and debrisfalls outside the moraine.As for the volumes of material involved, in the specific cited case, the first placeis occupied by movements of rock and ice, together with the depletion of barrierlakes(triggering of debris flows and jokulhlaup). Extremely variable volumescharacterise the falls of glacial fronts, whilst the debris falls from the moraine involveminimum amounts of material (Fig. 67).The combined analysis of these parameters results in particularly interestingobservations related with the fact that the hazard scale varies according to theparameter considered. For example, the depletions of endoglacial lakes are to beconsidered extremely hazardous on account of their rapid evolution, even if the watervolume can be less than that coming out from barrier-lakes. The latter are usually

152volumeFig. 67. Development times, propagation distances and debris volumes (water ± ice ± snow ± rock ±glacial and alluvial deposits) of the various instability phenomena. The most frequent ranges of valuesare shown (instability phenomena with propagation times, distances and debris volumes can take placealso outside the areas identified) (modified after Dutto & Mortara, 1993).characterised by slower depletions but with longer propagation distances.The same authors (Dutto & Mortara, 1993) tried to give a semiquantitativeassessment of the hazard derived from the phenomena considered (scarce; average;high) by drawing up a classification based on the repetitivity of single events, theperceptibility of possible premonitory signs and the relative hazard, defined as thesum of the hazards derived from the development times, the propagation distancesand the volume of the materials involved.3.6.12 AvalanchesThe phenomenon of avalanches has been known since the mountains have beencovered with snow and among the hazards recurring in the mountains, is the bestknown and most observed (Fig. 60). Probably it is about avalanches that mostforecasts and prevention measures are made. Moreover, it is one of the fewphenomena for which specific research agencies have been established, with thepurpose of prevention and elaboration of thematic maps showing the areas more orless affected by the phenomenon. For the study of avalanches mathematical modelshave been developed based on the analysis of numerous parameters. The consultationof any modem treatise on the subject emphasizes the quantity of physical, mechanical

153and meteorological data considered in this type of study and the complexity of theirtreatment.The vast knowledge about it is due to the fact that the people living in mountainvalleys are obliged for several months a year to put up with a kind of event affectingmuch wider territories than those occupied by glacial masses. Once the only kind ofdefence available for mountain people against this hazard was exclusively passive:buildings constructed in traditionally safe areas, Hmited winter movements, scarcepresence of human structures at high altitudes. Afterwards, the construction ofcommunication ways in any possible place as well as the development of tourism andwinter sports determined both a permanent and seasonal transfer of people towardhigh-hazard zones. A more active defence from avalanches therefore becamenecessary so their mechanisms had to be studied.The formation of avalanches due to spontaneous detachments takes place on thesnow masses when either an increase of stresses (agent forces) or a reduction ofresistance forces is observed. The former is mainly due to the accumulation of freshsnow (precipitations, wind), the latter can be derived both from destructive snowmetamorphism (passage from star-shaped crystal to spheroidal crystal) and toconstructive metamorphism (rapid growth of angle-shaped crystals) or to thetemperature increase (formation of lubricating levels owing to pore saturationperformed by melt water). Among accidental causes, the fall of debris and snowledges, thunder, explosions, passage of animals or skiers should be mentioned.Avalanche subdivision varies according to the criteria applied. According to thetype of movement, the first distinction is made between powder snow avalanches andflow avalanches. The difference between these two types is based on the velocity, theheight of the mass in movement, the density, the effect of topography and the flowtrends (Scheiwiller, 1986) (Table 11).Other subdivisions take into account the type of detachment, the position of thesliding surface, the ground morphology and the snow conditions (humidity) (Haefeli& Quervain, in Fraser, 1970; Fraser, 1970; Roch, 1980) (Fig. 68).TABLE 11Comparison between the characteristics of powdery-snow avalanches and those of skimming avalanches,according to Schiwiller (after Casati and Pace, 1991)Flow avalanchesPowdery snow avalanchesTypical velocity 30—60 m/s -100 m/sThickness of the massin movement

154Fig. 68. Schematic subdivision of avalanches, according to HaefeH & Quervain (in Frazer, 1970),modified.From the point of view of forecast it is possible to utilise a third subdivisionbased on the possible existence of a delay time between the meteorological event

155which causes the avalanche and its effective detachment. From this standpoint"immediate" avalanches are distinguished from ''delayed" avalanches. The former,with which the term meteorological avalanches is also associated, are formed aftera sudden variation of meteorological parameters (e.g., heavy rainfall, marked warmingup), whilst the detachment of the latter is ascribed to the slow transformations withinthe snow. In this second case it is, therefore, very important to know the localcharacteristics of the snow cover. It is obvious that in reality it is extremely difficultto make a distinction between immediate avalanches and delayed ones, but thispermits an understanding of how the aspects concerning the forecasting areconceptually different and also shows the data available.Avalanches often cause the loss of human lives and damage to property. To givean idea of the gravity of the phenomenon it is sufficient to quote that in the1965—1985 period nearly 2,000 people lost their lives in the Alps owing to theseevents. Those usually involved in this type of hazard are the inhabitants of villages,workers employed in construction works on mountain slopes, tourists and militarytroops operating in high-mountain areas. As for infrastructures, the artifacts andconstructions involved in these phenomena are mainly houses, communication routesand their infrastructures (bridges, underpasses, etc.).The consequences can be very serious, especially when human lives are lost: aperson cannot resist for long under an avalanche heap, especially because of theadverse thermic conditions. The type of aid, the promptness of the intervention andthe location of the person in difficulty is therefore the most important condition forsuccess (Fig. 69). As regards damage to infrastructures, besides the cases whenconstructions (such as houses, hotels, etc.) are directly struck, entire inhabited centrescan remain isolated for several days, even when not directly involved with logisticdifficulties linked to the electricity supply, the disruption of communications, the foodsupply, etc.The perfect knowledge of a territory based on complete historical and geomorphologicalstudies, aimed at the reconstruction of the past history of avalanches by meansof chronicles and evidences gained from direct surveys in the field, provide extremelyuseful information.Since these phenomena show a systematic recurrence and usually take place inconcomitance with analogous climatic conditions, it is of paramount importance tocarry out a series of environmental surveys. For this purpose the various boards incharge of the study of avalanches have already equipped a set of sample areas inwhich specialised operators record meteorological and nivometrical data.In particular, the stability of snow is part of the general problem of mechanicsgoverned by three groups of strictly interdependent parameters: meteorological,nivological (superficial and internal) and local parameters. The first two act also asindicators and together with a series of "visual" observations (e.g., the triggering ofsmall avalanches at high altitudes) are used for prevention purposes (Table 12).Meteorological parameters show extreme variability due to the different altitudinalbelts and to the important relief role which "generates microzones" characterised bydifferent climates owing to the "different orographic protection". The superficial

1561.00.8^ 0.6nOSno 0.40.20 1 2 3 4 5hoursFig. 69. Probability of survival for a person buried by an avalanche in function of the length of time,according to Roch, 1980.nivological parameters are continuously and directly surveyable (also automatically)whilst the internal ones are more difficult to obtain, since they can be recorded onlythrough manual operations at ground level (digging of trenches). Local parameters,if known and correctly taken into account, can be considered from time to time asconstants. The latter noticeably interact with meteorological parameters and, as aconsequences, with the nivological ones.The forecast of avalanche risks is still an open problem, based on models usingmainly deterministic and statistical approaches. Even if a large amount of objectivedata is available, practical experience teaches that a valid forecast is also greatlybased on the operators' experience and "well-founded confidence" in their work,blending the physical data with personal "intuitions" and local knowledge. Still withinthe framework of risk forecast, numerous attempts to lay out "decision-makingcharts" (flow charts) have been made, but the latter have shown some effectivenessand applicability only in simple cases, where no more than five variables (32 possiblecombinations) are taken into account.In the winter of 1993—1994 the need for avalanche reports according tostandardised scales, led to the drawing up of a single scale, with five levels of

157TABLE 12UNIFIED SCALE OF AVALANCHE HAZARD (Modified after Bassetti, 1994)(Valid from the 1993-94 winter season in France, Switzerland, Austria, Germany, Italy and Spain)Hazard scale Stability of the snow cover Probability of avalanche detachment1) Low The snow cover is usually wellconsolidated and stable2) Moderate The snow cover is moderatelyconsolidated on some slopes;in the remaining ones it is wellconsolidated3) Considerable The snow cover shows a weak tomoderate consolidation on manysteep'' slopes4) High The snow cover is poorlyconsolidated on most steeps slopes5) Very high The snow cover is in most casespoorly consolidated and unstableDetachment is possible only with highoverload^ on very few extremely steep'*slopes. Only small spontaneous avalanchesare possible (so-called discharges)Detachment is probable with highoverload^ especially on the steep'' slopesshown. Large spontaneous avalanchesshould not be expectedDetachment is probable with weakoverload^ especially on the steep'* slopesshown. In some situations medium-sizedspontaneous avalanches are possible and,in single cases, even large onesDetachment is probable already with weakoverload*" on most steep slopes. In somesituations many medium-sized spontaneousavalanches should be expected andoccasionally large onesMany medium-sized spontaneousavalanches should be expected even onmoderately steep" slopes"In the Avalanche Report the following parameters are described in a more detailed way: altitude,aspect, pattern of the ground, etc.^Overload: high) e.g., compact group of skiers, snowcat vehicles, use of explosives; low) single skier,ohneski excursionist.Definitions = steep slopes: slopes with angle over 30°; extremely steep slopes: slopes with unfavourablecharacteristics concerning inclination, ground pattern, proximity to crests and soil roughness;spontaneous: without man's intervention; exposition: cardinal point to which the slope is facing.hazards, valid for all the countries whose territories fall within the Alpine range(Table 12).Defence against avalanches is carried out by means of various types of interventionsthat can act either directly or indirectly on the snow cover or the avalancheitself. In areas characterised by a high hazard level, both rigid and elastic containmentworks, placed in adequately separated lines, are constructed with the aim ofstabilising the snow cover. For this purpose snow nets, racks and bridges made ofsteel cables, aluminium, wood and concrete are anchored to the ground with variousdevices. These works stand out of the ground at heights of a few metres and areusually inclined at about 15° downhill with respect to the perpendicular slope line.Another system of defence is given by the modification of the snow deposit by using

158barriers that reduce or accelerate the wind velocity as necessary. The deflectors,usually made of steel-wire and nylon nets, slow down the wind velocity by conveyingthe snow accumulation into nonhazardous areas. On the contrary, the acceleratorbarriers which exploit the "Venturi effect" increase wind velocity in the most criticalpoints, thus avoiding snow deposition. Temporary hazard situations can be solved inthe short term by means of artificial impulses on the snow cover by triggering aseries of small explosions. In this way large accumulations of snow are avoided andtherefore the fall risk is reduced. Other protections made of earth, stone, walls orconcrete can be installed; they mainly consist of channelising or diverting works,suitable to contain the avalanches in their natural slide paths or compelling them totake small diversions. The problem connected with this type of defence is given bythe dimensions of the artefact, usually constructed on the basis of previous events orestimates.Especially on low-angle slopes or flat land it may be useful to slow down theavalanche velocity to avoid the involvement of risk areas. In this case it is possibleto construct appropriate works such as dams, earth and stone barriers, butresses andbraking wedges. To protect roads, railways and inhabited centres, purpose-plannedworks, based on recent engineering technologies, have been constructed in recentyears, giving excellent results. Transport networks are usually protected not only bydefence works placed along the slopes but also with tunnels, walls and canopies.Large earthworks or wedge-shaped concrete embankments are located so as to protectbuilding sites, power lines, groups of buildings or entire inhabited centres.Besides all this series of interventions aimed at preventing and avoiding thetriggering of avalanches, mention should be made of the natural and effective"antidote" for avoiding or mitigating the formation of avalanches in proximity of thetree line: that is, the presence of woods. They absorb part of the snow from theground, supporting the snow cover with tree-trunks and prevent the formation ofshear fractures. Forestation and deforestation can, therefore, alter the evolution of aslope in some cases.The developing times of such a phenomenon are fast (Fig. 70) and the triggeringis quite sudden. It is possible to forecast that sooner or later there will be snowdetachment in a certain area, although the precise moment is not foreseeable. Onlythe distance between triggering zone and strike area (structure, person, etc.) can insome cases allow people a few moments to find shelter or run away. The situationsderived from the movement of fast powdery avalanches (>50 m/s), during whichdestructive pressure waves preceding the arrival of the avalanche itself aredetermined, are particularly critical.As for communication routes, some alarm systems capable of blocking the transitin correspondence with systematic avalanche paths have been set up.It is practically impossible to make a choice and quote disastrous examples ofavalanches owing to the great number of cases occurring every year. The press, someperiodicals and specialised reviews notify the amount of damage caused to people andproperty every year during the winter season.The hazard of this phenomenon is so serious that specific thematic maps have had

159150h 500 km/hh 400Powder avalancheb 1008h 300y U0)x:ocmIh 20050100 ^Surface avalancheBottom avalancheFi^Om/sO0 cm 50 100 150200Height of snow in cm70. Relationship between avalanche velocity and height of snow (modified after Roch, 1980).250to be drawn up in order to give the most complete picture of the phenomenon. Thesemaps have been compiled by official research boards and/or military corps, on thebasis of historical investigations, field enquiries, geomorphological surveys, analyseson the state of vegetation and information deduced from the analysis of aerialphotographs. Usually the areas which have already been struck by avalanches areshown on these documents and subdivided according to the type of source used fordata collection. Also the zones exposed to avalanches, those considered hazardousand the locations of their tracks are traced on these maps. The avalanches, progressivelynumbered and named as regular, periodical and exceptional, are described insingle cards. For each episode, the fall frequency, slope orientation, detachment, slideand accumulation areas, historical and statistical records plus any other usefulelement, are indicated. Figure 71 shows an example of avalanche map. The relativelegend is that utilised by the "Experimental Centre for the study of snow, avalanches,Alpine meteorology and hydrogeological defence" of the Forestry Department of theRegion Veneto, Italy (Fig. 71).3.6.13 Rock glaciersAnother source of hazard in high-mountain regions is given by the presence of rockglaciers, especially those that are still active. They are frozen bodies of detritus whichin the form of lobes or tongues slowly descend en masse along slopes or valleys.Their lengths range from a few hundred metres to over one kilometre. Their presence

160Intersection of partcular areas forphotointerpretation arxl field surveyFORC i> P6R0SAFig. 71. Map of probable location of avalanches in a Dolomite area (Municipality of Auronzo di Cadore,Belluno, Italy). (From: Centro Sperimentale Valanghe e Difesa Idrogeologica, 1986, modified).is strictly linked to rigorous thermic conditions, since they are remnants of adiscontinuous permafrost. In the Alps they are usually found above 2,500 m andusually affect slopes and valleys where the mean annual temperature is below -1—2°C(Haeberli, 1985).Rock glaciers are considered a geological hazard almost exclusively from theengineering point of view. Their movement and/or deformation velocity, althoughhigh, can always be kept under control and therefore will not cause direct damage topeople. Most active rock glaciers move at surface velocities ranging from 0.5 to 1m/year"'. In the Yukon (Hughes, 1966) velocities up to 250 cm/year"' were recorded,in Switzerland (Chaix, 1943) up to 131—161 (surface) cm/year'; usually they varybetween 73 and 5 cm/year ' (Giardino, Shroder & Vitek, 1987), yet a 5 to 10cm/year"' velocity is sufficient to destroy most of the structures built on rock glaciers.Rock glaciers can cause three principal types of damage to structures: damageresulting from gross active movements, from other deformation processes and bysloughing material. Specific bibliography considers the hazard of this phenomenoncomparable to that of landslides, moisture-sensitive soils or active faults.Surface deformation can cause damage to structures owing to differential bedrocksettlements. The latter can be determined by partial ice-melting within the rockglacier or by removal of the finer fraction by means of running waters during thaw.

161Deformations were observed also in active and nonactive rock glaciers, followingartificial cuts or excavations. Besides generating disturbances in the thermic regimeinside the detrital body, this type of activity triggers en-echelon tension cracksparallel to the cut and surface distortions behind the cut face. Owing to the abovementioned causes, also compression-hnked deformations are associated with thesettlements of surface layers (surface layer compression is a short-term phenomenonand would occur very quickly after or during appHcation of structural loading).Even structures placed in the proximity of rock glaciers can be subjected todamage. Large boulders can collapse from the front or more seldom from the sidesin a few minutes, owing to the different velocity assumed by the surface with respectto the deeper parts (surface velocity is usually greater than that at depth). Pylons,power lines, posts, ski lifts, radio repeaters and any other prevalently vertical structurecan be slowly tilted. In these cases use of supports and relevelling operations mustbe considered. Also transport infrastructures such as roads and railways requireconstant maintenance in order to maintain their original direction (if they areconstructed on rock glaciers) or reconstruction works if transit has been obstructedby the advancing front. Pits and tunnels that go through these landforms are subjectto considerable deformation, owing to tangential stresses, and to high pore waterpressure exerted by melt water. In particular, tunnels and pipelines should havedirections which comply with the flow trend of the rock glacier.A good prevention norm means avoiding the positioning of towers, pylons, powerlines, etc. on active rock glaciers which should not be intercepted by roads, railways,tunnels, pipelines or other structures. Also the forms considered inactive can at timesgive some problems.Correct procedures would require a field survey to be planned, accompanied bya series of investigations aimed at verifying the presence and the rate of activity ofrock glaciers. When interference with these forms is inevitable, all possibleconstruction devices and remedies should be put into practice in agreement with thegeotechnical expertise developed during construction in areas subject to permafrost(Biyanov, 1976; Andersland & Anderson, 1978).In rare circumstances rock glaciers can generate barriers along valleys or formnarrowings. Sometimes the latter are considered for dam abutments. In the specificliterature it is recorded on that rock glaciers have been used as abutments for damsto retain mine tailings in Colorado.Warning signs of instability are: the formation of a surface microrelief, fannelshapeddepressions and longitudinal, meandering troughs. The analysis of thermicinfrared remote sensing imagery can reveal the presence of permafrost inside thestructures considered. A check of aerial photographs taken in different periods willallow the eventual advance and velocity of the front to be recorded. Geophysicalborings (in particular geoelectrics), BTS measurements and possible drillings couldgive evidence of the presence and type of ice inside (ice-cored or ice-cemented rockglacier). Geomorphological hints of activity are given by the bulging shape of thewhole mass, the steep front with a bank of rocks at the toe, the surface ondulatingand modelled in a series of grooves.

162Foster & Holmes (1965) reported the case of blocks rolling from an active rockglacier in Alaska up to a distance of 26 m. In the La Sal Mountain (Utah), the sameauthors observed mass failures on the front of a rock glacier from an angle of 52° to40°, with debris moving 81 m down the valley. During the construction of a railroadin Colorado, nearly 100 years ago, rock glaciers were encountered. Several activerock glaciers were cut through by mining-tunnels in Colorado (Brown, 1925).Giardino (1983) points out that in one of these (Mt. Mestas) remarkable deformationsoccurred. The collapse of an adit and raising in Camp Bird near Ouray, Colorado,were ascribed to deformations of an active rock glacier (Griffiths, 1976 in Giardinoet al., 1987).3.6.14 Debris flowsDebris flows are flows of sediments and water that go down to a valley floor alongtraditional water paths (torrential riverbeds) or along slopes through new routes. Thistype of event, which develops following the sudden influx of large amounts of wateron loose soils is particularly frequent in high-mountain regions. Heavy precipitations,snow melt water, phenomena such Sisjokulhlaup on glacial, torrent and slope depositsare the cause of the phenomenon. The volumetric ratio between water and sedimentsand the different dimensions of the debris itself create a differentiated series ofmovement types known as earth flows, mud flows, grain flows and debris avalanches(Fig. 72). Usually the debris flow deposits are poorly selected and are recognised onthe ground because they make up typical banks and lobes.In most cases the debris flow deposits are not very specific and are recognised onthe ground because they form typical banks and lobes. According to the volume ofmaterial involved and especially of the amount of water, they run over distancesranging from a few tens of metres to several kilometres, with velocities up to 30—40m/s. In a high-mountain environment debris flows are found along the flanks ofvalleys, troughs and torrent riverbeds, mobilising the unconsolidated sedimentscovering the slopes and the deposits obstructing the bottom of valley floors. Somecan also be periodic and recur in the same areas after a certain number of years,perhaps in relation with the time necessary for the formation of debris to substitutethat carried away during the previous event.Small-sized debris flows which develop along the top portions of slopes orcanyons usually mobilise debris fans or cones and can be hazardous, especially forroad networks: footpaths, trails, muletracks, mountain roads, etc. A greater hazard isfound with those channelised within torrent beds which generate alluvial fans or areinserted in them. Alluvial fans are very often highly populated areas owing to thefavourable conditions which they offer to man's settlement compared with valleyfloors. The areas most at risk, i.e., those that can be subject to debris flows andfloods, are the apical ones and those located along the torrent axis.In other situations, debris flows, regardless of their dimensions, can create barriersacross streams resulting in the formation of impoundments. The phenomenon is quitefrequent at confluences, when the mass of debris transported suddenly loses energy

163riverWATERstr earnFINEDEBRISCOARSEDEBRISFig. 72. Types of debris movements connected to the volumetric ratio between water, debris and thedebris different grain-size (modified after Haeberli and Naef, 1988).owing to widening of the hydraulic section and is deposited. The Hfe and dimensionsof the impoundment will depend exclusively on the topographic conditions, the debrisparticle size characteristics and, most of all, the erosive capacity of the dammedwatercourse.The forecast possibilities are practically nonexistent, since it is not possible toknow in advance the quantity of water involved nor the length of time it will remain.As a consequence in mountain regions most of the areas covered by loose debris arepotential sources of mud flows.Prevention measures can be either passive or active. In the first case thedevelopment of areas considered hazardous should be avoided, in the second, effortsshould be made to reduce the probability of debris flows. As regards slopes andcanyons, the first measures to be taken should attempt to stabilise debris withafforestation techniques or the construction of weirs, secondly accumulation materialsthat could turn into flows should be removed. The nearer the first intervention is tothe debris zone of origin (middle and higher parts of the basins), the more effectiveit will be. On large alluvial fans prevention will be carried out by means of defences(embankments, barriers, groins) to divert or channelised the debris.

164On the basis of a series of investigations aimed at the study of debris flows in theAlps during the 1987 floods it was realised that apart from occasional events, thistype of phenomenon normally takes place over wide areas of territory (Haeberli &Naef, 1988). The event is the result of the interaction of various main factors that are:— the presence of loose debris in canyons, fans and areas in front of glaciers(following the retreat of the glaciers themselves, the snow fields and thepermafrost);— the presence of a large amount of melt water often due to a delay in thawing,because of late snow falls;— the presence of loose material saturated with water following heavy springprecipitations;— the raising of thermal zero.Moreover, the slope angle of the debris surface should not be neglected, the presenceof watercourses fed by melt water at the edges of the deposits and a stagnation ofgroundwater next to the surface (rock and/or permafrost). On the basis of theseconsiderations it is obvious that the knowledge and monitoring of these factors canbe useful for the prevention of the phenomenon.3.6.15 Final remarksBy analysing the series of phenomena that take place in high mountain regions(glacial and periglacial morphoclimatic environment) and the connected hazard,experience has shown that in many cases it is extremely useful to know about thebehaviour and past history of a phenomenon. Reports and historical records notalways register all the events; moreover the most ancient ones could not be recordedor those that happened in areas far from the presence of man. The growth of ancientmountain settlements and their transformation into villages, the exploitation ofmountains for tourist-sport purposes both in summer and winter and the need toconstruct new communication routes, has led to the occupation of areas that not longago were the absolute domain of phenomena linked to mountain evolution dynamics.Knowledge of the ''geological" history of these areas is therefore possible onlyby means of a correct and exhaustive analysis of the landscape and its forms. Forhazard assessment in mountainous environments it is therefore extremely necessaryto perform a basic geomorphological-type study aimed at recognising single eventsoccurring in the recent geological past, by considering the surface deposits and thesigns left in the morphology and vegetation cover. By identifying, defining and datingthese traces it is possible to reconstruct both the sequence of the events, in a relativeand often absolute chronology and their patterns of occurrence. From thesereconstructions the areas exposed to risk and the frequency of the phenomena can berecognised. Moreover it is possible to identify portions of territory that at first sightwould seem to show no hazard but which in remote times underwent various degreesof damage. In order to carry out all the programme listed before, it is necessary touse more "information markers" which would make use of analyses performed ontopographic maps, in the field and on aerial imagery.

165Another element to be taken into account for hazard assessment is the phenomenon'sreturn-time: for this purpose it is necessary to specify temporally the variousevents recorded on the ground. In a high-mountain environment the datingtechniques of dendrochronological, lichenometric and '"^C type on organic remnantssuch as peat deposits, fragments of wood, buried soils, etc., are particularly effectiveand useful.3.7 Geomorphology and seismic risk3.7.1 Seismic riskLike the definitions shown in chapter 1.6, seismic risk may also be considered as the"product" of the seismic hazard and the social and economic vulnerability of a givenarea.Therefore, it will be defined as the probability of an earthquake of a preestablishedmagnitude occurring within a given number of years, with specificconsequences for the environment. Thus, seismic risk is defined not only by theexpected seismic event itself, but rather, by the setting of this event in the geologicaland physical-geographical conditions of the area affected, in the density of thepopulation, in the conditions of existing buildings and constructions, in the type ofeconomy, in the level of preparation for and knowledge about seismic events on thepart of the population, in the presence of aid facilities and in the efficiency of thecivil defence network. In fact, the factors making up the definition of seismic riskmay be summarized according to the outline shown in Fig. 73 (Panizza, 1991).In a strict sense, seismic hazard connected with the earthquake and the seismotectoniccharacteristics of an area, is distinguished from seismic susceptibility; the lattercorresponding to a hazard induced by the physicogeographical situation of the areaconsidered. Seismic hazard should refer to the types, features, mechanism, andyseismic hazardearthquakecharacteristicsf /MagnitudoJ focus area dimensions] hypocentre\^etc.seismotectonic f seismicity \rorjcharacteristics | tectonic structures jr^^LSEISMIC RISK < seismicsusceptibility(lithobgygeomorphologyhydrogeologyetc.\vulnerabilityexposureeconomysocial organizationprogram planFig. 73. Outline witli the factors converging into the definition of seismic risk.

166phenomenology of earthquakes, that is, to the energy they propagate, to the depth atwhich they occur, to their recurrence according to time sequences that may even berelatively brief, to the dimensions of the focus area, etc. This type of hazard is alsolinked to seismotectonic characteristics or, in other words, the relationship betweenthe focus and faults identified on the surface by geological methods or inferred atdepth through seismological studies.As far as seismic susceptibility is concerned, the term refers to local, geological,morphological, hydrological and other factors, of both the surface and the substratum,which may amplify or reduce seismic vibrations or create situations of precariousgeomorphological equilibrium.The geomorphological studies applicable to seismic risk assessment can bedivided into two sectors (Fig. 74):a) morpho-neotectonic investigations conducted to identify active tectonic structures;andb) geomorphological and morphometric analyses aimed at identifying the particularsituations that enhance or reduce seismic susceptibility.These two sectors will be discussed in the following chapter.3.7.2 Morpho-neotectonicsMorpho-neotectonics is that part of Structural Geomorphology that deals with the"relations between landforms and recent tectonic movements" (Panizza and Piacente,1978b).I morphoneotectonics[^"^TECTONICSTRUCTURESEISMIC SUSCEPTIBILITY(local conditions)(SEISMOTECTONICS^V'^y^•-.SEISMIC HAZARD(earthquake expected)rfsURFACE EFFECTsYi'^^ WIMIHIHIMIHIIII^liimniHiiwiiiiHiwiiiiniiniiHiimtwiiMiiiiiiiwitiHniiiiiiHiHje"GRAVITATIONAL" EFFECTS(mass movecDflfTts)EARTHQUAKECHARACTERISTICS^ -• meVtodoiogica} way'nxxphoneottctonks •• surface faults'VULNERABILITY"•'•"«•» methodological waytoc^ conditions-- mass movements'Fig. 74. Two different methodological Geomorphology contributions for seismic risk assessment.

In this multivariable natural system, recent tectonic movements are considered asan internal variable within the system, whereas all the other geomorphological causes(climatic conditions, azonal agents, morpho-selection, etc.) are considered externalvariables, that is, outside the system (see Panizza & Piacente, 1978b). Viewpoints arenot unanimous regarding the chronological interval defining the "neotectonic" timeperiod. This time period may encompass an age that ranges from the Miocene to thePresent, to time segments limited to the Quaternary alone or even only the latter partsof it. For example. Oilier (1988) gives the following four definitions of Neotectonics:1) tectonic movements during the present and the recent past; 2) tectonic movementsduring the Neogene and Quaternary'; 3) legal use related to so-called ''capablefaults"\ 4) the tectonic activity that created the present topography.Morpho-neotectonic research is based on the concept that tectonic movementshave brought about changes in the Earth's surface. The identification of such changescan therefore allow the neotectonic movements to be traced back to their origin andthus permit an appraisal of the likelihood of their continuing or of others occurringin the future. With investigations of this type and thus through the identification ofactive tectonic structures, geomorphology contributes to the assessment of an area'sseismic hazards. Another consideration to be made, concerns the relations betweenmorpho-neotectonics and morpho-selection. In fact, the latter proves to be inverselyproportional to the former. In other words, the more recent and intense the morphoneotectonicactivity is, the less time is available for morpho-selection to manifestitself. For example, in a recent fault scarp, the selective differentiation on the variousrock types present is generally not very prominent.Several morphological features make up "peculiarities" from a strict morphogeneticviewpoint which can be signs of neotectonic deformations (Panizza et al.,1978). In Fig. 75, some particular kinds of slopes, valleys and hydrographic networksresulting from tectonic movements are illustrated. For example, a hnear ridge can bethe result of a fault scarp evolution or correspond to its upper part or show a regionaluplift. An altimetric ridge discontinuity can be determined by a crest-transversal fault.A particular definition is that of "capable fault" (see Caggiano, 1979):a) A ''capable fault'' is a fault which has exhibited movement at or near the groundsurface at least once within the past 35,000 years or movement of a recurringnature within the past 500,000 \ears (United States Atomic Energy Commission,1973).b) A fault which has been active during the Late Quaternary (International AtomicEnergy Agency, 1972).A scarp can be associated with a vertical fault or an areal uplift: on its surfacetriangular or trapeziform facets can be produced. Reverse slopes and areas affectedby landslides and particular erosion forms can be linked to faults. Valleys with simpleor double river bends can reveal the presence of a horizontal fault. A movement ofthis kind could also produce fluvial barbed or upstream confluences. Irregularitiesfound in some valleys, such as overhanging confluences or truncated valleys can belinked to faults subject to various movements. Relief landforms of this kind or similarfeatures can therefore be an indication of recent movements and after having been167

168Fig. 75. Schematic examples of particular morphostructures resulting from neotectonic movements: a) faultscarp and counterslope (Bastardo basin, Tevere valley, Italy; after Gregori, 1988); b) fault scarp withfacets; c) fault and double river bends; d) fault and landslides.selected, verified, deepened and quantified, they can give substantial evidence ofthem. It is in any case opportune to remember that the morphological evidence of aneotectonic movement is connected with its velocity and with the velocity ofgeomorphic processes (which, in turn, are related to lithology, climate, etc.)-Morpho-neotectonic studies are generally organised according to the followingphases, in increasing order according to the degree of detail provided.(1) Bibliographical research: the collection, processing, and interpretation ofbibliographical data that indicate or infer the existence of neotectonic displacements.It is undertaken primarily in order to track down information on the distribution ofPlio-Quaternary deposits as well as tectonic elements and any tectonic activity. Thisresearch should be consolidated in the form of a map of the Plio-Quaternary depositsand tectonic elements.Another aim of bibliographical research is to collect data that may be utilised forthe specific objectives of the study. Thus, it is useful, for example, to carry outstudies on the seismicity of the area in question and elaborate the data into a map ofseismic epicentres as well as studies on vertical movements of the ground, both recentand in progress, to be synthesized in the form of isolines relating to the whole of themovement and studies on geothermal or volcanic phenomena, etc.(2) Regional remote sensing: satellite image interpretation for the identificationand selection of lineaments of natural origin and their possible neotectonicsignificance. Each selected lineament is individually described and reproduced on amap on the same scale as that used for the map of Plio-Quaternary deposits and

169tectonic elements. The comparison between these two maps allows their differentelements to be qualified and subdivided into three categories:1) Tectonic elements that are probably active.2) Lineaments that may be linked to possible active tectonic elements.3) Tectonic elements that are probably inactive.For example, the faults taken from bibliographical analysis, which are superimposedon Plio-Quatemary deposits and coincide with a selected lineament taken from remotesensing, should be inserted in the first category.The second one includes the selected lineaments not corresponding to tectonicbibUographical elements which, nevertheless, show sufficient evidence andcongruence of signs of morpho-neotectonic features. In the same category alsomorpho-neotectonic signs overlapping on Plio-Quatemary deposits are indicated.In the third category all the tectonic elements that do not correspond to anyselected lineament and that do not overlap Plio-Quaternary deposits are indicated.In any case, it is obvious that among the examples above described there areseveral intermediate cases which will have to be individually analysed. Also thecoincidence with lineaments of seismic epicentres of superficial earthquakes isimportant.(3) Aerial photograph interpretation: listing and selection of geomorphologicalevidence of tectonic activity and related lineaments. The first operation to be carriedout consists in an aerial photograph-based census of all the neotectonic geomorphologicalindications, their selection and representation on topographical maps accordingto the legend shown in Fig. 76. The second procedure consists of the identification,guided by geological data, of landforms resulting from inactive tectonics or rather,from passive structures. These are then eliminated leaving only lineaments withhypothetical neotectonic significance. The lineament direction, length and location areindicated on the data sheet, together with aerial photographs on which wereidentified, the geological deposit involved, relevant bibliographical references and anypossible correspondence with the elements drawn from phases (1) and (2). Allrelevant geomorphological features must be reproduced with observations as to theirquantity, quahty, congruence, distinctness and freshness. During the same phase ofaerial photo-interpretation itineraries for field checking are chosen and subsequentlyrepresented on topographical maps, together with notes on the specific field-checksthat are to be carried out.(4) Field survey: verification of the neotectonic hypotheses and precise geometrical,geological and geomorphological specifications of any existing tectonicstructure. Field records should include explanatory notes, geological sections, plans,photographs, geological maps or other types of maps, depending on the case in hand.A data sheet should be compiled for all lineaments, reporting in particular thegeological characteristics of both the bedrock and the superficial deposits, as well astheir interrelationships. Geomorphological features should be specified and any othersupplementary datum recorded. Every lineament must then be interpreted from aneotectonic point of view. If it corresponds with a fault, the type and direction ofmovement and, if possible, the amount of neotectonic displacement should also be

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On the basis of the above specified morpho-neotectonic studies, a subdivision ofthe lineaments according to the following categories is established (Panizza,Castaldini et al., 1987).1) Active tectonic element: recorded displacement and/or deformation of rocks and/orsignificant forms.2) Tectonic element supposed to be active: so defined on the basis of numerousqualified and congruent geomorphological indications, or of other sources. Thereare no visible rock displacements and/or deformations nor significant landforms.The presence of an inactive fault or tectonic deformation is in any caseascertained from geological evidence.3) Tectonic element supposed to be inactive: so defined on the basis of scanty, nonqualified and noncongruent geomorphological indications, or of other sources.There are no visible rock displacements and/or deformations nor significantlandforms. The presence of an inactive fault or tectonic deformation is in any caseascertained from geological evidence.4) Inactive tectonic element: displacements and/or rock deformations are notascertained. The presence of an inactive fault or tectonic deformation is in anycase confirmed.5) Qualified lineament: with numerous, qualified and congruent geomorphologicalindications or of other kind, but showing no outcrops capable of confirmingdisplacement and/or deformation.6) Unqualified lineament: with unquahfied or noncongruent geomorphologicalindications and showing no outcrops capable of confirming displacement and/ordeformation.7) Lineament not corresponding to tectonic elements: so defined when showingnumerous and/or qualified and/or congruent geomorphological indications, butwithout any ascertained displacement and/or rock deformation.It should be noted that the term "significant" is used for rocks and forms to indicatethat their age lies within the neotectonic interval considered.The elements derived from morpho-neotectonic studies are listed in a specificthematic document called morpho-neotectonic map (Fig. 77).These morpho-neotectonic studies contribute to the definition of a neotectonicsynthesis, together with investigations in other fields of Earth Sciences: for example,the results of seismo-tectonic investigations, or those concerning the main fracturedirections of rocks. The synthesis document is a neotectonic map, like the one shownin Fig. 78.Also in this sector of Geomorphology, as for the treatment of all geomorphologicalphenomena, the temptation to indulge in schematizations must be resisted asthese could lead to inappropriate deductions and interpretation errors due to thegeomorphological convergence of landforms which are outwardly similar but in factare genetically different. Remaining in the field of morphoneotectonics, the significantexample could be quoted of asymmetrical valleys which show tilting phenomena inone direction or the other, according to the erodibility of the rocks, the rate oftectonic movements and the intensity of fluvial erosion processes. Another example171

1722) 0 a, b, cFig. 77. Examples of morpho-neotectonic map. Legend: 1) classified lineaments; 2) field check-points;see Fig. 76 for morpho-neotectonic symbols.is offered by a series of fluvial terraces distributed on various levels: the latter canshow several orders corresponding to different stages of evolution or to the sameorder involved in various tectonic displacements.3.7.3 Geomorphology and seismic susceptibilityAs mentioned above, there are particular geomorphological situations that can conditionseismic susceptibility. In other words, these situations can offer local responsesto seismic acceleration, causing mitigation or amplification of earthquake intensity.In order to calculate seismic acceleration, the following variables should beknown:— magnitude, frequency of occurrence and distance of seismic events;— material sequences for each point of the terrain, as well as geotechnical data suchas density and seismic wave velocity;

173ACTIVE1) 0 0 0HELD TO BEACTIVE4) • -7) >^5) —3)-6) +Fig. 78. Examples of neotectonic map. Legend: 1) anticline; 2) syncline; 3) fault; 4) qualified lineament;5) area undergoing subsidence; 6) area undergoing uplift; 7) tilting. Compare with Fig. 77.— groundwater levels;— topographic conditions.There is specific literature on the various geomorphological, geological, geotechnical,hydrogeological situations, among others, that can influence seismic effects in anegative or positive manner. Only specifically geomorphological parameters will bediscussed in the following. Those of a geological type (lithology, contacts betweendifferent rocks or deposits, presence of fractures, etc.), geotechnical type (particle sizedistribution of the deposits, degree of consolidation, mechanical characteristics, etc.),hydrogeological type (presence and depth of the water table) or others will not bediscussed here and specific works should be consulted on these topics. It should bementioned that research in this sector of applied sciences is still at an initial stage,in which the results have not yet permitted the indication of precise methods ofevaluation, model procedures or seismic effect calculations, unless the circumstancesare relatively uncomplicated. In most cases, qualitative assessments may beformulated, based mainly on the consequences of recent earthquakes and theinteraction of their effects.

174The most important geomorphological situations that can condition seismicsusceptibihty, are the following:~ Slope angle.~ Debris.~ Morphology.^ Degradational slopes.— Paleolandslides.— Underground cavities.3.7.3.1 Slope angleIt is well known that, in a static situation, with other variables being equal (lithology,moisture, etc.), slope instability increases with the slope angle. In other words, slopestability is inversely proportional to slope angle. In the dynamic situation of anearthquake, the instability of a slope and consequently that of any buildings on it willbe greater than in a static situation. For the towns located in the Campania andBasilicata regions affected by the earthquake of the 23 November 1980, the ItalianNational Research Council (CNR) Finalised Project "Geodynamics" (1983) adopteda correction coefficient (Sp) for the buildings and structures located in seismic areas,which depends on the slope angle, as follows:5/7=1 + 1.5/where / is the mean slope angle expressed as a percentage. The ^/^-coefficient, whichexpresses the increase in seismic activity, is multiplied by the seismic coefficient C,which defines the force employed for the seismic testing of constructions (C = 0.1for the earthquake regions in the first category; C - 0.07 for those in the secondcategory).In any case, the CNR Finalised Project '^Geodynamics" (1983) advises againstconstruction under the following conditions in the case of slopes with an mean slopegradient /° greater than the established limit. This limit depends upon the type of rockor deposit, as shown in Table 13.3.7.3.2 DebrisThe slope deposits made up of cohesionless materials, as in the case of talus, morain,TABLE 13Slope angle limits for several types of terrains, according to stability during seismic shocksIncoherent debris (including cataclastic debris), with water table depth >10 m 20°Incoherent debris (including cataclastic debris), with water table depth 10 m 25°Clays of compact texture, but very "tectonized" and/or fissured 10°/° limit

175TABLE 14Increases in seismic intensity for some types of debris, compared to graniteRock typesSeismic intensityGranite 0Pebbles and gravel 1—1.6Sands 1.2-1.8Clays 1.2-2.1alluvial deposits, etc., generally give rise to geomorphological situations that canamplify seismic susceptibility. More specifically, increases in seismic intensity canbe linked to three factors:a) surface slope angle of the debris;b) its particle size characteristics;c) thickness of the deposit.The debris slope angle has already been considered in the more general case of thelast section and the reader is referred to it for details.Particle size distribution can significantly enhance seismic intensity. It is outlinedin Table 14, modified from Medvedev (1965) with some simplifications. Somecohesionless rock types are compared with compact granite, under conditions wherethere is no water infiltration. This infiltration can further increase seismic intensityup to values of 3—4, approximately.The thickness of the deposit also plays a part in amplifying seismic intensity. Inthe case of deposits thicker than 5~10 m, Siro (1985) indicates critical thicknesses onthe basis of the most probable frequencies of the arriving vibrations and the averagepropagation velocities of the transverse waves, which determine the amplifications ofseismic intensity. For velocities of transverse waves from 200 to 600 m/s, the criticalthicknesses resulting are shown in Table 15, along with the proposed correspondingcoefficients of amplification ranging from 1.5 to 2.5.3.7.3.3 MorphologyAn amplification of seismic intensity resulting in an increase in damage to buildingshas often been observed in correspondence with particular morphological situationsTABLE 15Critical thickness of debris, compared with the velocity of transverse seismic waves, with ampHficationcoefficients ranging from 1.5 to 2.5Average velocities (m/s) Critical thickness (depth in m)200 8-40300 11-60400 15-80500 19-100600 23-120

176such as crest lines, terrace borders, scarp edges, or abrupt variations in slope gradient.These amplifications appear to be due to phenomena involving the concentration ofseismic rays that are reflected as a result of their different inclination angles, with respectto the vertical, corresponding to sudden topographical changes. Studies aimedat investigating this topic (Castellani et al., 1982) indicate amplifications as great as3.5.Similar amplification phenomena have been observed in correspondence withburied morphological structures, such as paleoriverbeds or fossil terraces or forms oferosion masked by superficial deposits. There are also cases involving seismic rayconcentration phenomena, due, however, to refraction phenomena where the anglesof incidence are shown to differ from the vertical. In the intervention projects plannedfor the towns of the Campania and Basilicata regions (southern Italy) affected by theearthquake of November 1980 (CNR Finalised Project "Geodynamics", 1983), 10-20-m reserve zones were advised in correspondence with rocky crests, isolated summits,terrace edges and border areas of steep scarps.3.7.3.4 Degradational slopesThe amount of weathering on slopes and therefore the degree and type of rockdegradation taking place can affect seismic susceptibility.For example, in the Friuli earthquake of 1976 (northern Italy), there werenumerous debris falls from the slopes of the Tagliamento river valley and those ofits tributaries. The debris ranged from small or isolated rock fragments to largeboulders and rock falls of vast proportions (Fig. 79). The survey and mapping ofthese mass movements by Govi and Sorzana (1977) revealed that most of the rockFig. 79. Rock fall caused by earthquake in 1976, Braulins (Friuli, Italy) (Photo M. Panizza, May 1976).

177falls occurred prevalently in places where there had previously been other gravitationalevents. Geomorphological surveys have revealed the different sources of thedebris accumulations and their different ages of formation.Observations on the area led to the indication that the phenomena, occurredprevalently in calcareous rocks showing intense tectonic fracturing, which are subjectto strong frost weathering. This type of disturbance was much less frequent in thecase of the earthquake of southern Italy in 1980, even though there are slopes in thearea made up of calcareous rocks, some of which have been intensely fractured bytectonic activity. Frosty weathering is lacking in this area or, in any case, it is muchmore limited compared with the Alps.Frost action exerts a slow and progressive degradation of the rocks. In the caseof seismic shock, the fragments detached are not only unbalanced debris, whichwould have fallen in any case on account of frost action and gravitational processes,but also include material that is still partially attached to the rock or on slopes lowerthan those with detached fragments. It is as if the seismic shocks complete a sort of"cleaning operation" on the slopes, eliminating the weathered material.Studies aimed at the assessment and identification of areas subject to this type ofseismic susceptibility must consider not only the sector beneath slopes or scarpsundergoing degradation processes, which can be affected by rock falls or otherlandslides, on the basis of gravitational mechanisms alone. They must also considerthose areas that can be reached by boulders thrust by strong seismic shocks beyondthe gravitational fall limit or set into a rolling motion and movement because of theso-called "vibrating table" effect.An investigation on the limits of maximum advance of fallen boulders followingthe 1976 Friuli earthquake, was carried out by Onofri and Candian (1979). By meansFig. 80. Slope parameters considered by Onofri and Candian (1979) for an investigation on the limits ofmaximum advance of fallen boulders following the 1976 earthquake in Friuli (Italy).

178of a statistical analysis on 98 cases of rock fall, the authors have set up twodiagrams for the definition of the boulders' maximum advance limits for each singleslope angle (Fig. 80). In the first diagram (Fig. 81) the parameters taken into accountare: H (altitude of fall or vertical height between the detachment point and the arrestone) and D (projection on the horizontal plane of the distance between A and B).These parameters totally prescind from the morphological pattern of the slope onyi = Dm 14001300120011001000 H900 H800700 H600500^400300200 Hlimit of predictability 95%limit of predictability 90%limit of predictability 80%100100200 300 400 500 600 700 800 900 m#^ Xi = HFig. 81. Diagram of the limits of maximum advance of fallen boulders following the 1976 earthquake inFriuli (Italy) prescinding from the morphological pattern of the slope (after Onofri and Candian, 1979).

which the boulders fall. In the second diagram (Fig. 82), also the influence of theslope morphology on the path followed by the boulders is considered. The parameterstaken into account are: the ratio between the area Ap subtended by the slope profile,with respect to the horizontal plane, and the square number of the fall height (H');and the 0^ angle (inclination of the energy line). For each of the two diagrams thelimits of confidence of 80, 90 and 95%, respectively, have been calculated.1793.7.3.5 PaleolandslidesEarthquakes sometimes set into motion older landslides (see 3.7.4). The villages ofCalitri, Bisaccia, Senerchia and other localities in southern Italy affected by theNovember 1980 earthquake, are emblematic examples of this. The landslides occurredin mainly clayey rocks, in flysch facies, sometimes chaotically arranged or highlytectonised. They affect stretches of land several kilometres long with a transportinvolving hundreds of millions of cubic metres of material.A slide affecting the village of Calitri in the province of Avellino started to movea few days after the seismic event, involving about 23 million cubic metres of material.Its sliding surface was calculated at a depth of over 100 m. The movement correspondsto a partial reactivation of a pre-existing rotational slide (Hutchinson & DelPrete, 1985) evolving downslope into earth flows that reached the Ofanto river,modifying its course. Cotecchia (1986) maintained that pore-water pressure, whichincreases noticeably in concomitance with seismic vibrations in clayey and flyschoidrocks in tectonic contact with water-saturated calcareous strata, must have played avery significant role in triggering into motion the paleolandslides of this region. It hasbeen demonstrated (Agnesi et al., 1983) that earthquakes lead to an increase in theoverall size of landslide bodies, yet without significant modifications of their shapeand typology.3.7.3.6 Underground cavitiesEarthquakes in calcareous areas with underground karst processes can cause the fallor collapse of cave roofs or the removal of debris from rock cavities. The consequenceson the surface are depressions or subsidence of the ground with the resultingdanger of collapse for the buildings located above.limrt of predictabiWylimft of pnedtctabiNtylimit of predictability95

1803.7.4 Earthquake-triggered mass movements'^*by Doriano CASTALDINI3.7.4.1 Worldwide examplesEarthquakes are considered to be a major triggering cause of mass movements inmany geological materials.One of the first earthquake-triggered landsHde was documented as early as372—373 B.C. when Helice, a Greek city on the northern coast of the Peloponnese,sHd into the sea after having been razed to the ground (Marinatos, 1960; Seed, 1968).Many other examples occurred in historical times such as the mass movementsproduced by the earthquake at New Madrid (Missouri) in 1811, at Kansu (China) in1920, at Chait (USSR) in 1949, in California in 1957, in Alaska in 1964 and in Japanin 1978 (see Hansen and Franks, 1991).Data from 40 historical worldwide earthquakes were studied by Keefer (1984) inorder to determine the characteristics, the geological environment and hazards oflandslides caused by seismic shocks. One of the main results obtained by Keefer(1984) was to define relative levels of shaking that triggered landslides in susceptiblematerials. Four types of internally disrupted landslides — rock falls, rock slides, soilfalls and disrupted soil slides — are started by the weakest shaking. More coherentmaterials with deep-seated slide surfaces, require stronger shaking while lateralspreads and flows are triggered by even stronger shakings, but the strongest shakingis probably required for highly disrupted rock avalanches and soil avalanches. Suchtopic was further investigated by Keefer and Wilson (1985, 1989).At a more general level, many detailed investigations have been carried out allover the world in order to assess the relationships between earthquakes and massmovements (see Plafker et al., 1971; Nilsen & Brabb, 1975; Solonenko, 1977; Youd,1978; Harp et al., 1981; Perissoratis et al., 1981; Sorriso-Valvo, 1986; Wue Cai &An Ning, 1986; Geh et al., 1988; Rymer & White, 1989).In more recent times a conference on slope stability in seismic areas wasorganised (Faccioli and Pecker, 1992); a special session on "Seismicity andLandslides" was held during the 16th International Symposium on Landslides (seeBell, 1992) and landslides certainly triggered by earthquakes have been described inJapan (Yamagishi et al., 1993) and in California (Jibson et al., 1994).More specifically, as reported by Bell (1992), a huge landslide in Iran, occurringduring the 21 June 1991 Manjil-Roodbar earthquake, with M 7.3 magnitude, wasanalysed (Anvar et al., 1992). This slide started the day after the earthquake andcontinued for several weeks threatening the blockage of a road used for emergencyoperations and the filling of a large reservoir of a dam along a downstream river.In Crozier (1992) a methodology for determining paleoseismicity is discussed anddemonstrated for three earthquake-triggered landslides in New Zealand, whileaccording to Naumann & Savigny (1992) the five major rock avalanches that haveoccurred in SW British Columbia since the end of the last glaciation are at leastlikely to have been triggered by high pore-water pressure increase caused by seismicshock.

181Other authors, from a general point of view, show how the effects of anearthquake on a slope depend on several natural factors (such as the characteristicsof the shock, the slope angle, the properties of the rocks and soils involved, the porewaterpressure, etc.) as well as irrational human activities (such as deforestation,inadequate land use, etc.) contribute to further deterioration.After analysing the relationships between earthquakes and mass movements ona world-wide scale, Cotecchia (1987) remarks that the behaviour of a slope affectedby an earthquake depends on the nature of the ground motion, the slope geometry andits composition. Indications of the likelihood of mass movements under nonseismicconditions do not always hold good for landsHdes triggered off by earthquakes.Ground shaking can produce accelerations within the soil mass, accompanied by asystem of stresses that can completely alter the strength of the materials. Thus whenconsidering the response of a slope to accelerations that vary in amplitude anddirection, the dynamic properties of the ground cannot be ignored (Cotecchia, 1992).Moreover, it is opportune to remember that Cendrero & Dramis (1994), in ageneral survey on landslides in Europe, noticed that in areas subject to seismicinfluence, both the size of individual landslides and the total areas affected tend tobe somewhat greater, but no significant differences exist in typology and morphometrybetween recent earthquake-triggered movements and older, presumablyclimate-triggered ones. This suggests that seismicity does not change the style oflandscape evolution, but it probably increases its rate. This is confirmed by the factthat only 5% of the area affected by landslides after an earthquake corresponds tofirst-motion movements. The remaining ones are reactivations of older movements.3.7.4.2 Examples in ItalyOne of the first reports on earthquake-triggered landslides in Italy is by Vivenzio(1788) who described the geomorphological effects produced by a catastrophicearthquake which struck Calabria (southern Italy) in 1783 (Cotecchia et al., 1969).Several other historical records and oral traditions exist about gravitationalmovements triggered by earthquakes in Italy (see, for example, Oddone, 1915 and1931; Govi, 1977; Govi & Sorzana, 1977; Genevois & Prestininzi, 1981; Serva, 1981;Dramis et al., 1982; Pellegrini & Tosatti, 1982; Crescenti et al., 1984; Zecchi, 1987;Murphy, 1993; Mazzini, 1994).The characteristics of some mass movements connected with the two majorearthquakes occurring in Italy in the past 20 years (Friuli, north-eastern Italy, andCampania and Basilicata, southern Italy) will now be examined.The earthquake that occurred in Friuli on May 6, 1976, with a main shock ofmagnitude 6.4 and intensity IX-X (Mercalli scale), produced several surface effectsover an area of more than 1,600 km' (Weber & Courtout, 1978). The most strikingsurface effects were given by the numerous landslides activated by the earthquake(Govi & Sorzana, 1977). They mainly consisted of rock falls and, to a lesser extent,block-slides involving rock volumes of up to 100,000 m\ especially on calcareousslopes with high relief energy. Fractures, visibly opened as a result of the earthquake,appear to outhne many of the gravitational forms (Govi, 1977).

182The results of the above mentioned investigations on the relationships betweenthe landslides and the Friuh earthquake are here given in detail:— the photo-interpretative method for the survey of landslides connected with anearthquake was found to be adequate for rapidly acquiring an overall picture ofthe effects triggered on the slopes by seismic shocks;— most of the landslides triggered by the Friuli earthquake were rock falls whichtook place mainly where these phenomena had already occurred in the past;— important factors influencing the landslides at an equal distance from theepicentre, were the weakening of the rocks by intense tectonic fracturing and thesteepness of the slopes controlled by lithological and structural conditions.Further studies (Girardi et al., 1981) carried out in the area struck by the 1976earthquake, have emphasized that the whole area along the front of a pede-Alpineoverthrust shows evidence of the close connection between seismic events and largescalelandslides ascribed to Late Pleistocene. The latter appear to be rock slides alongbedding planes or faults.The latest high-intensity earthquake in Italy (with a main shock of 6.8 magnitudeand intensity X (Mercalli scale) happened on November 23, 1980 and struck a vastarea in southern Italy, especially in Campania and Basilicata regions (Deschamps &King, 1983; Westway & Jackson, 1987).The most evident surface effects of the earthquake were mainly due to massmovements of various types, in relation with the lithological and structuralcharacteristics of the bedrock (Cantalamessa et al., 1981; Cherubini et al., 1981;Genevois & Prestininzi, 1981; Cotecchia, 1982; Maugeri et al., 1982; Agnesi et al.,1983; Crescenti et al., 1984: Cotecchia & Del Prete, 1984; D'Elia et al., 1985 and1986; Hutchinson & Del Prete, 1985: Cotecchia, 1986; Carton et al., 1987; Fenelliet al., 1992; Bisci & Dramis, 1993). These events mainly occurred immediately afterthe main shock, their movement becoming completely or almost exhausted in a shortperiod.Block-slide phenomena, bordered by earthquake-induced fractures were fairlyfrequent. The huge landslide 3 km in length that occurred in a pelitic-arenaceousbedrock at San Giorgio in Molara was of this type. From eye-witness accounts andhistorical data, it seems that this has only moved in association with earthquakes(Genevois & Prestininzi, 1981; Dramis et al., 1982). At Trevico, Dramis & Sorriso-Valvo (1983) observed lateral spreading in an area of conglomerates resting on clays.The event consisted of the deepening, amounting to some decimetres, of a smallgraben-like depression (50 m long, 15 m wide and 2 m deep) located on a hill top.For this form too, testimonies from local inhabitants refer to activation correspondingto previous earthquakes and no disturbances within aseismic periods.Another huge mass movement showing recurrent activity and accompanyingseismic events involved the whole town of Bisaccia in Campania, even if thedisplacements were limited. This landslide has been described also recently by severalresearchers: Crescenti et al. (1984), D'Elia et al. (1985), Esu et al. (1985 and 1987),FeneUi (1988), Fenelh & Picarelh (1990), D'Elia (1991), Fenelh et al. (1992), Bisci& Dramis (1993).

1833.7.4.3 Study methodologies in ItalyAt present various studies on the evaluation of landslide hazard in seismic areas arebeing carried out in Italy. For example, the investigations in north-western Tuscanyrequire detailed geological and geomorphological surveys (1:5,000 scale) in order todraw up a stability map. This will show active and dormant landslides, as well asareas potentially exposed to mass movements due to their morphological and lithologicalfeatures (see D'Amato Avanzi et al., 1993).An interesting study project on earthquake-triggered landslides is being carriedout by Genevois (1994). It is schematically represented in Fig. 83 and is heresummarised.The existing data bank phase is based on bibliographical research on earthquakes(consulting seismic catalogues for historical, instrumental and macroseismic data anda consequent selection of the study areas on the basis of isoseismal maps, e.g.,minimum VII of intensity (MCS scale), and on the distribution of epicentres andlandslides (references of catalogues and historical archives, requests to publicauthorities such as Council Boards, Districts, Regions, research agencies andUniversities; detailed reviews of scientific articles and magazines).The phase of identifying earthquake-triggered landslides implies the correlationand assessment of the data acquired in the previous phase.The identification of earthquake-triggered landslides is carried out by means ofcorrelations that can be of direct or indirect type.With relation to the direct correlation, the method is based on the identificationof landslides occurring simultaneously with the seismic event {direct landslides) orcertainly set into motion some hours or days after the seismic shock {indirectlandslides).Indirect correlation is carried out on the basis of the morpho-structural and/ortopographic characteristics (very low gradient angle) of prehistoric landslides or onthe basis of documented simultaneity between seismic event and mass movement. Inthe latter, with temporal concomitance a 4—5-day time-interval is intended, betweenearthquake and landslide, although obviously some problems remain when the dateof the earthquake or of the subsequent landslide is not known.The evaluation of the correspondence between earthquakes and landslides can begood (if direct or indirect correlation is io\\nd)\ fair (if the interval is a little longerthan the time span or if a careful location of the landslide is not possible, e.g., morethan one in the same area, or an approximate date of the earthquake) or nocorrelation (time interval too long, uncertain location of the landslide, very ancientlandslide, too vague a date for the earthquake).The next step consists on the compilation of landslide cards. This phase of theresearch is based on a collection of data (geological, geomorphological, hydrogeological,tectonic and neotectonic, geotechnical, geomechanical, climatic,seismological) and other possible integrations (geological and geomorphologicalsurveys, photogeological analysis, in situ investigations, laboratory tests, landslideclassification, statistical data analysis). The final content is given by a completegeological model, that is a geotechnical-geomechanical model, an isoseismic-line map

184(^HISTORICALAND BIBLIOGRAPHICAL RESEARCHES^(EARTHQUAl

185and related parameters), static analyses (back analysis, parametric studies, finite anddistinct elements solution), pseudostatic analyses (Sarma's method or others,parametric studies such as Kh, r^^, c, O) and dynamic analyses (Newmark method,methods simulating time history of induced stresses and assessing pore-water pressureand strain development).On the basis of the investigations so far described, the analysis of the correlationbetween geological and geotechnical macro-categories (lithology, slope aspect andangle, mechanical behaviour) and earthquake parameters (intensity, magnitude,distance, directivity) are defined.This logical sequence is based on the combination that a multivariate analysis ofthe factors involved in post-earthquake-induced landslides may be useful, if notessential, in finding the relationships between these two phenomena. This knowledgeshould therefore be considered as the starting point of any evaluation of possiblefuture scenarios in any area of particular interest. The ending topic of this researchwill be, as a consequence, the analysis of the probable behaviour of sample areassubject to possible future earthquakes.Many earthquake-induced mass movements show a more or less direct connectionwith other surface effects of seismic activity, in particular ground fractures and faults(see, for example, CavaUin et al., 1977; Carton et al., 1978; Bollettinari & Panizza,1981, Fig. 84; Carmignani et al., 1981; Cinque et al., 1981). These features may bepreserved and, therefore, paleoseismological studies may detect and date them,thereby permitting extension of knowledge beyond the local historical threshold (upto 2,000 years in the most fortunate cases).In recent times, it has been possible to survey directly, with scientific methods,surface effects of strong earthquakes (Panizza, Castaldini et al., 1987; Vittori et al.,1991; Galli and Meloni, 1993) also comparing them with the historic and instrumentalseismicity of an area. The above mentioned papers illustrate criteria which may aidin the identification of areas suitable for paleo-earthquake investigations. Historicalseismicity and the presence of well developed geomorphic tectonic features arerecognised as the most reliable criteria for identifying active faulting.3.7.4.4 ConclusionsThe real causes of earthquake-triggered mass movements are not completelyunderstood. Nevertheless, according to existing studies and taking into account theresearch experience in Italy, it is possible to express some final remarks.First of all, mass movements induced by seismic events are mainly grouped intofive types: rock slides, debris slumps, rock avalanches, rock falls and soil slides. Thetypology and dimensions of earthquake-triggered landslides are related to both thegeological environment of the site and the characteristics of the seismic shock. Forexample, inertial forces due to rapid loading may cause falls and toppling in rockmasses, whereas a number of documented cases of landslides due to liquefaction ofsaturated loose sand highlight the role of pore-water pressures induced by seismicshaking. In clayey deposits, several factors can interact in a complex pattern, thusproducing variable effects. Sometimes it is possible to recognise long-term

186Fig. 84. Surface fault near San Gregorio Magno (Salerno. Italy) caused by the November 1980 earthquake(the photograph was taken by M. Panizza immediately after the event).displacements as the delayed consequence of pore pressure build-up induced by cycl ICloading.Many of these phenomena (mostly the largest ones and deep-seated gravitationalmovements) show atypical recurrent demobilisation (stepwise activity), beingreactivated only as a consequence of very strong seismic shocks; it could, therefore,be quite difficult to recognise them a long time after the last seismic event. Moreover,It can be argued that many landslides (both dormant and active) owe their firstactivation to a strong earthquake in the past.Many mass movements (mostly slow ones) are started only some days after the

187main shock. It has also been observed that quite frequently earthquake-inducedlandslides reach the valley bottom, thus causing displacement of the watercourses or,sometimes, their damming. Earthquake-triggered mass movements are also connectedwith other ground effects such as fracturing and faulting.With reference to the studies on these phenomena, as already observed by Bisci& Dramis (1993), it is often possible to identify areas affected by earthquake-relatedmass movements also starting from fast survey (such as photo-interpretation), evenif more particular investigations are the only way to provide more precise informationabout seismic influence on landscape evolution.Detailed geomorphological survey and mapping of earthquake-prone areas is ofbasic relevance for land management, since it constitutes the main tool for assessingpotential slope instability in case of seismic shocks. In this framework, in order todetermine the evolution of unstable slopes, geological, structural, geophysical andpaleoseismological analyses must play a major part in any investigation to be carriedout. Extremely detailed studies can also rely on the monitoring of earthquake-inducedlandslides.Once more, the importance of considering earthquake-induced mass movements(and, more generally, surface effects) in the evaluation of global seismic hazard andrisk should be emphasized, since what might seem a marginal aspect can quite oftenbe a major factor in determining the real local situation.Finally, it is opportune to point out that seismicity does not change the style oflandscape evolution but probably increases its rate.3.8 Geomorphology and volcanic hazardThe evaluation of the hazard determined by volcanic eruptions depends upon severalfactors. First of all, on the type of activity.Basaltic lava effusions, for example, are characterised by slow and intermittentflows and generally by low-intensity explosions. Therefore, as far as risk for thepopulation is concerned, these eruptions are usually slow enough to permit a safeescape but all that cannot be removed like houses, crops, etc., are in most casesdestroyed. In some cases attempts to divert lava flows have been made. In the caseof Mt. Etna, for example, in 1669 some men equipped with metal bars managed toshift part of the lava by reducing the speed of the main flow. More recently, in 1983,a partial diversion was achieved by means of explosive charges. Even more recently,in 1992, in order to divert a lava flow which entered a subterranean canal and reemergedalong the slope threatening an urban centre located downhill, the inlet of thecanal was obstructed with boulders transported by helicopter, thus diverting andslowing down the flow (Fig. 85). Similar other attempts were carried out in Hawaiiin 1935, 1942, 1955 and in 1960, when several walls were constructed near Kilaueawhich partly succeeded in confining a lava flow.Explosive eruptions, are on the other hand, much more dangerous, in particularthose that produce clouds of incandescent ashes and avalanches and pyroclastic

188Fig. 85. Scheme of the interventions carried out for the defence of Zafferana, during the Etna eruption(Sicily) of 1992.flows. Whilst effusive eruptions seldom reach high velocities, incandescent cloudscan attain a velocity exceeding 100 km/h and exert an enormous destructive power.They run down valley floors and can overwhelm also hills and small reliefs, levellingthe morphological features of the volcano's lower slopes and covering distances ofup to dozens of kilometres. In terms of risk, whole towns can be destroyed andprobably the best known example is that of Pompeii, wiped out by the eruption ofVesuvius in 79 A.D. This ancient Roman town was completely buried within 2 daysunder the volcanic ash fall-out, which killed over 15,000 people. Even morecatastrophic was the case of St. Pierre in Martinique which was destroyed on 8 May1902 by a vast explosive cloud coming down from Mt. Pelee, claiming 30,000 lives.In these cases the only way out would have been a preventive evacuation of theinhabitants.Also the starting up of pyroclastic ejecta movement on volcanic slopes causes avery serious hazard in some areas of the Equatorial belt, with the formation of the socalled lahars. The latter are high-density mud flows usually determined by intenserain fall, which run down along the valleys at the toe of the volcano, causing fargreater damage and casualties than the eruptions themselves. In other cases, such asin Indonesia, the phenomenon can be caused by a sudden depletion of a crater lake.Recently, on 13 November 1985, the Nevado del Ruiz volcano (Colombia) started anexplosive activity with modest ejection of ash and pumice: the eruption was sufficientto melt the volcano snow cap, triggering a vast mud flow which struck the town ofArmero killing 25,000 people. For the defense against some kinds of lahar connected

189with crater lakes, containment walls or lake-draining tunnels have been adopted inIndonesia.Other parameters for the evaluation of volcanic hazard are given by the eventcharacteristics, the quantity of erupted material, the transport mechanism, eruptionenergy, magma fluidity, etc. (see Barbed & Gasparini, 1977).Also the reconstruction of the history of volcanic effusions brings importantcontributions for the hazard assessment of various kinds of volcanoes, both in termsof extension and direction of the phenomena (Sheets & Grayson, 1979).The most up to date knowledge of volcanic risk is based on the activity associatedwith the most recent and best known eruptions, such as Mt. St. Helens, about whicha full book has been written dealing with warning signs and patterns of behaviour tobe assumed in these circumstances (Saarinen & Sell, 1985).As for the forecasting of eruptions, the observation of several volcanoes hasallowed various phenomena to be considered as signs warning of an imminent eruption.They are: the melting of snow caps, the disappearance of crater lakes, the dryingout of wells and springs, the withering of the surrounding vegetation and the flightof animals and birds. Nevertheless, the modem methods of forecasting are based oninstrumental measurements such as (see Oilier, 1988): the monitoring of earth tremorslinked to the magma ascent; tilt measurements of swellings or tumescences causedby lava pushing inside the volcano; temperature measurements of crater lake, hotspring and fumarole waters; measurements of the composition of gases erupted fromcraters or fumaroles; measurements of changes in local gravity and magnetic fieldslinked to lava movements at depth. Still in the field of forecasting, methods based onthe recurrence of eruptions and on the relationship with other events such as sunspotsor moon phases have also been elaborated. For a detailed knowledge of modemindicators of volcanic forecasting, see Tazieff & Sabroux (1983) and Decker (1985).The contribution of Geomorphology in volcanic hazard assessment dealsessentially with the influence that the local conditions of a relief can have on thedirection and velocity of flows. Valley cuttings and depressed areas, directly connectedwith the emptive vents, are the most favourable flow and accumulation routesfor the magmatic advance. Obviously the high gradient slopes correspond to the mostrisky areas for human settlements when other hazard conditions remain equal.The collection of all these data for each volcano can lead to the drawing up ofmaps showing a territory's volcanic hazard potential. An example of this kind isoffered by the lava invasion hazard map (Fig. 86).Moreover, climatological and meteorological studies can indicate the areas mostsubject to possible invasion of volcanic ashes or other products linked to windintensity and direction (see Sheets & Grayson, 1979).3.9 Geomorphological hazard mapsSeveral examples of this kind of mapping can be found in literature, with applicationsin many parts of the world, showing the most varied geomorphological stability

190MAP OF THE NEVADO DEL RUIZVOLCANIC HAZARDPYROCUSTIC FALL^V^i_>-Type1595A.D.'^Z^Fig. 86. Example of a volcanic hazard map: Nevado del Ruiz. Colombia (modified after Parra, CepedaandThouret, 1986).conditions. In this paper the situations directly derived from the author's experiencewill be described, with reference to the Italian territory which, unfortunately, offersa great variety of geomorphological hazards: from landslides to soil erosion, frombadlands to river erosion, from subsidence to beach degradation etc. (see Panizza &Piacente, 1978a; Panizza et al., 1980; Gruppo Geografia Fisica e GeomorfologiaCNR, 1987; Amanti et al., 1992).The author's founded conviction is that in order to create a geomorphologicalhazard map it is necessary to operate keeping separate and afterwards comparing, onthe one hand, the causes of instability (natural context and human activities) and, onthe other hand, the effects of instability (geomorphological history and dynamics)(Fig. 87).It is opportune to keep "causes" separated from ''effects" on account of thefollowing considerations:— the logical simplicity of the operative system;— the possibility of measuring/verifying the role of the various instability parameterson the basis of unstable forms actually observed;— a multidisciplinary approach with the possibility of applying concrete contributionsfrom various specialists in Earth Sciences.

191analysis of theCAUSESnatural contextgeologyhydrologyclimatemorphologyland useetc.humanactivitiesgeomorphologicalhistorypresentgeomorphologicaldynamicsGEOMORPHOLOGICALDYNAMICSGEOMORPHOLOGICALINSTABILITYFig. 87. Logical scheme for the determination of geomorphologicalinstability.3.9.1 Causes of hazardAmong the causes that favour or prevent instability, the following could be cited:geological, hydrogeological, topographic, climatic, and land use. Included amongman-induced causes are all human activities, such as hvestock-rearing, agriculture,engineering works etc., as they can all modify the environment. The analysis of allthese parameters which favour instability could be shown on an Integrated AnalysisMap (lA). Both the natural and anthropic contexts will also indicate the limits withinwhich geomorphological instability may develop, taking into account that someparameters remain constant (e.g., lithology, the force of gravity, etc.) and others vary(e.g., human activities, neotectonics, etc.). In other words, it will be possible to definethe range of variability, e.g., for predictable landslides in a certain area, over aspecified time period, both in terms of volume and quantity: it will thus be possibleto estimate that in the course of 10 years, one to five landslides could occur, with amaximum volume of 100 m"* each. As another possibility, one could predict, forexample, that in one year the soil loss due to rill wash on a particular slope will reach100 tons over 1 km".In order to elaborate an Integrated Analysis Map, it is therefore necessary tooverlap and compare the various basic elements that are the predisposing hazardcauses within a given territory. The instability degree of a certain portion of land isalways the result of the interaction of two or more causes acting through complex

192mechanisms and the influences of the different factors involved may either besummed or multiplied. As a consequence, the rating of each single cause withouttaking into account its interconnection with all the others, is to a certain extent anabstract and incomplete operation. This is particularly true in areas characterised byrecent orogenesis, like in Italy, where poorly cohesive and highly deformed rocksoutcrop. The same areas are subject to uplifting phenomena and are therefore affectedby extremely intense geomorphological dynamic processes. Moreover, if unfavourablerainfall regimes are associated with these factors, then the most hazardous instabilityconditions will coexist and interact. In this framework, it is nevertheless difficult toascertain the relative importance of each of them.The characteristics of the materials ascribable to their composition, texture,structure, stratigraphy, pedology, alteration, etc., all belong to the geological causestogether with their tectonic history and that of the territory where they crop out.Particular importance should be given to the distinction between active tectonics andtectonics with a passive role only. It must be emphasized that within each geologicalbody, the zones characterised by a different degree of chemicophysical alterationshould, as far as possible, be identified and mapped separately. This natural processis in fact of paramount importance since in time it causes a progressive decline of theintrinsic resistance of the materials making up a slope. Also erosional processes dueto rillwash or superficial mass movements are largely controlled by the rate and typeof rock and soil weathering (Carson & Kirkby, 1972; Coates, 1980).As for hydrogeological causes, the role of water on slope instability can beconsidered inferior only to the force of gravity: this applies to the actions ascribableboth to superficial hydrology and to percolation, storing and migration of waterunderground. Various phenomena are connected to the action of water, such as:runoff and the deriving processes of sheet, rill and gully erosion, solifluction relatedto rock impregnation, subsidence, river erosion or sand and silt liquefaction, whencohesionless materials are subjected to seismic shocks, etc.Among topographic causes various aspects of slope geometry are included: slopeangle, altitude (relief energy), length and shape of the slope, all are morphologicalelements that control instability in different ways and to different extents (Demek ed.,1972; Carson & Kirkby, 1972; Cotecchia, 1978). One should also consider that thanksto the recent developments of computer technology the basic data of the existingtopographical maps have been acquired in automatic and semiautomatic ways.Moreover, it has been possible to automatically produce a wide range of documentsrepresenting the above listed morphological factors over wide areas.As regards climatic causes, it is well known from literature (see, for example,Derbyshire, 1976; Starkel, 1976) that a large number of slope instability phenomenatake place under the effect of rainfall. For example, in some kinds of landslides (soilslip, debris flow) mostly affecting the superficial cover, their constant associationwith pluviometric events often of high intensity leads not only to the identificationof the threshold values beyond which the displacement occurs but also to theassessment of the return times of extreme precipitations. The problem may becomemore complex when mass movements involving large rock volumes are considered.

193These landslides often affect a considerable thickness of the bedrock and can respondwith a certain delay to a precipitation, owing to the geotechnical characteristics of thematerials and the groundwater patterns of circulation. In these cases an important roleis attributed to the length of the precipitations, rather than their intensity.The problems related to land use causes are mainly determined by farming,grazing and forest-management activities, that is by the kind of vegetal cover which,to various extents, protects the soil (see 4.2). This action can take place in thefollowing ways: by reducing the mobilisation and transport processes due to theactions of gravity, wind, water, etc.; by favouring the percolation of rainwater andtherefore limiting the runoff; by determining a barrier effect against all processes ofphysical degradation; by intercepting large amounts of rainwater for their biologicalactivities, etc. In particular, an analysis of the vegetal species should be carried outas well as a subdivision of the territory according to their level of ''impedance", thatis the power of protecting soil from erosion. Also the slope management and interventiontechniques should be considered (e.g., terracing or other farming methods).3.9.2 Effects of hazardThe analysis of effects is based on a geomorphological investigation that offers anoverall picture of the forms and processes of instability, both past and present, thisshould result in a Geomorphological Dynamics Map (GD). Such an analysis shouldalso provide a reconstruction of the geomorphological history of the most disastrousevents which have occurred in the area. A study of geomorphological dynamics isconcerned both with forms of erosion and forms of accumulation. These two typesof landforms may be considered separately or in their interaction. The study of pastevents should lead to a better understanding of the magnitude, frequency and type ofphenomena which reflect geomorphological instability. A comparison of present-dayprocesses with past geomorphological events will lead to an estimate of anevolutionary trend for instability. For example, a history of cliff retreat could becompared with present-day rates of coastal erosion or the recurrent flooding of a plaincould be compared with present-day rates of fluvial sedimentation.The identification of the most frequent and significant disarrangement phenomena,and therefore also of their determining causes, allows the investigations on thepredisposing elements previously illustrated to be concentrated on them.The effects of geomorphological hazard are essentially traceable back togeomorphological dynamics processes and their deriving forms, distinguished alsoaccording to their state of activity. The latter can be subdivided into the following.Active landforms: including those produced by ongoing processes at the time ofsurveying and those due to processes not taking place at that time but recurring inshort cycles (frequent, seasonal, etc.).Dormant landforms: corresponding to features characterised by geomorphologicalevidences or witnesses (direct, historical, etc.) of activity within the presentmorphoclimatic system which have objective possibilities of reactivation since theyhave not completed their evolution. These landforms can furthermore be subdivided

194according to their recurrence, that is the length of their inactivity intervals (e.g.,periods shorter than a century or longer).Inactive landforms: including both those ascribable to morphoclimatic conditionsdifferent from the present ones (e.g.. Pleistocene glacial landforms) and those which,although being produced by the present morphoclimatic system, have accomplishedtheir evolution and cannot change any further (e.g., terraced alluvial riverbed nolonger reached by flow waters).Figure 88 illustrates a simplified legend referring to the most frequent phenomenaamong geomorphological hazard effects on the Italian territory. Mapping of this kindis easily deduced from a detailed geomorphological survey.3.9.3 Synthesis of surveyBy analysing the list of the geomorphological hazard effects (see Fig. 88) it ispossible to deduce some of them correctly by considering the overlapping ofpredisposing causes (such as landslides and solifluction). Other geomorphologicalhazard effects, although depending on several causes, show their frequency in spaceand time (when, for example, a watercourse shows a tendency to deepen its riverbed).In other situations an evaluation of the hazard effects can be rather difficult anduncertain and a reliable forecast of their occurrence could be made only with difficulty(e.g., certain processes of man-induced degradation).As a consequence, when a hazardous area has to be recognised and properlyassessed by means of the reciprocal influence of the "causes", not all the "effects"Hsted in the corresponding legend will be considered, but mainly those deriving fromthe following types of slope movements:— falls and topples;— slumps;— slides;— flows, solifluction, gelifluction:As an example, for the landslides of the first group mainly the geological, hydrogeological,climatic and topographic causes will have to be considered. As for flows,solifluction and gelifluction, the geological, hydrogeological, climatic and land userelated causes will have to be taken into account.As regards other geomorphological processes, such as sheet, rill and gully erosion,the deductions of potential hazards can be based only on a limited number of causes(e.g., lithology and land use) and on a hypothesis of extension or not of the ongoingphenomena (effects). The latter can be obtained from measurements and monitoringof the process itself.After the first two phases of survey and data acquisition regarding the geomorphologicaleffects and of definition and assessment of the predisposing causes, it isnecessary to compare them. In fact, only the comparison and critical discussion of thetwo documents (map of integrated analysis and map of geomorphological dynamics)will lead to the elaboration of a synthesis document (Geomorphological Hazard Map)showing both the areas actually unstable and those potentially unstable, subdivided

195degradationai orlandslide scarperosional river scarperosional marine orlacustrine scarperosional glacial orcryogenic scarpACTIVE DORMANT NON ACTIVE

196a priori to a series of parameters that interact in time and space and from one areato the other in various ways. Their real role in causing instability conditions is noteasily ascertainable.For this reason, an analysis system concerning the relationships between causesand effects should be provided. Such a system should be "open" and reproduceable.For every study area it should therefore be possible to identify the type and numberof causes playing a role in the various instability processes, by applying a statisticalmodel relating every instability parameter to the unstable forms and processesactually observed in the field.Let us consider the work on Monte Santa Giulia (Panizza et al., 1980) in orderto illustrate an example of implementation of a document of this kind. The map ofgeomorphological hazard was obtained by overlapping the two analysis documents:the map of integrated analysis (lA) and the map of geomorphological dynamics (GD).This operation led to the following four different combinations.1) Indications of instability in the GD which do not find evidence for the sameprocess in lA. This means that the present hazard phenomenon has led to amodification of some of the predisposing parameters (e.g., slope angle, vegetation,etc.).2) Indications of instability in the lA without instability overlapping for the sameprocess in the GD. It is therefore deduced that the hazard process has not yettaken place.3) Coincidence of unstable sectors for the same process, deduced both from the mapof integrated analysis (lA) and from the map of geomorphological dynamics(GD). This shows that potentially unstable areas (lA) are developing this tendencyat present (GD) since they are in effect subject to degradation, and also that theongoing instability finds optimal conditions for further development.4) Overlapping of unstable sectors as a result of different processes. This can showthat the present degradational processes tend to develop and evolve according tophenomena that are different from those deduceable from the combination ofvarious causes.Any discrepancy between the two maps can obviously be ascribed to a lack ofsufficient data for the lA or to missing points in its elaboration.As a conclusion, it is opportune to emphasize that for the elaboration of thisgeothematic map two operations are extremely delicate:— the parametrisation, quantification, subdivision into various classes (for example,slope angle classes); and— the evaluation and attribution of their weight in triggering instability conditions(e.g., whether a certain kind of lithology or of precipitation is more destabilising).To solve the problem correctly, it is necessary to carry out, every time and for eacharea, a calibration and assessment on a "regional" basis, avoiding generalisations thatcould not have any practical or scientific foundation.

1974 MAN AS GEOMORPHOLOGICAL AGENT**by Sandra PIACENTE4.1 An approach to the problemMan is a geomorphological agent who was originally multizonal, but has progressivelybecome azonal up to the present day. Unlike other agents, such as water, ice,wind and volcanoes, he is not limited or localised but, on the contrary, is less andless conditioned by environmental variables.Compared with other living creatures, Man has a great capability of movementand adaptation: his activities on the environment are a result of his technologicaldevelopment and are guided by economic, social and cultural needs.Man transforms, corrects and modifies natural processes by increasing ordecreasing their rate of action and by causing the rupture of certain equilibria whichNature will try to reconstitute in different ways. With the passing of time thismodifying action has assumed increasingly widespread and intense patterns.The perception and awareness in scientific terms of Man's geomorphologicalactivity is very recent even if some scientists had already hinted at the effects on thenatural environment of an economy centred on intense farming in the colonial periodof North America. It was the American geographer Marsch (1864), in the middle ofthe last century, who recognised the disturbing influence on the natural environmentexerted by Man, considered as an agent modelling the Earth's surface. In the sameperiod, the great French geographer Reclus (1871) admitted that although the actionof Man can improve the value of the natural environment, it can also contribute toits degradation. In particular, he stated that: 'It is the improvidence of the inhabitants,and not so much the geological constitution of the soil, which is the principal causeof the devastating action of streams". For example, in the mountains of Provenceduring the course of centuries, the destruction of the vegetation cover related to theexpansion of farming land and pastures has contributed to the destruction of theoriginal landscape.Subsequently, the Russian scholar Woeikof (1842—1914) reconsidered the ideaspreviously expressed by Reclus and Marsch and ascribed some climatic variations tothe practice of deforestation. At the beginning of the twentienth century the Germanwriter Friedrich connected the term Raubwirtschaft, that is devastation, to Man'sactivities. In fact, he believed that: "The destructive exploitation of resources leadsof necessity to foresight and to improvements, and that after an initial phase ofruthless exploitation and resulting deprivation human measures would, as in the oldcountries of Europe, result in conservation". In 1901 the Italian geographer DeMarchi, in his "Trattato di Geografia Fisica" maintained that: ''Man modifies to hisadvantage vegetation, reliefs, hydrography and the coasts" and concluded by sayingthat: "with the diffusion of civilisation and the discovery of some new dominantforces of Nature, Man's geographical action is becoming increasingly intense,widespread and uniform to the point that it is already possible to forecast that it will

198become a main morphological agent".Still in those years (1915), the German scholar Fischer published the book ''DerMensch als geologischer Faktor", where a quantitative evaluation of the volume ofnatural material used by Man for the construction of roads and buildings is made. In1922 the British writer Sherlock in one of his works deals with the various aspectsof anthropic activity on the environment. In 1929 the French agronomist Aufrere inhis book on agriculture ''Les rideaux etude topographique" dedicated a chapter toMan as ''geomorphological agent". In 1935 the volume entitled "Man as a modellerof Earth", by the German author Fels, was published. In 1951, Mensching, anotherGerman writer, made an interesting correlation between the accumulation of siltymaterial in the Weser valley and deforestation on the river's upstream slopes inhistorical epochs.In 1953 the French author Tricart used the adjective ''erosion agent" referring toMan. In 1956 the proceedings of an international symposium on ''Man's role in thechanges on the Earth's face" were published.In 1959 the Italian geologist Gortani in his "Compendio di Geologia", in thechapter dedicated to the causes of mass movements attributes to Man's actions suchas large quarry excavations, slope cuttings, deforestation and farming practices, theresponsibility for some of these movements; although he considered these activitiesas "occasional causes which accelerate the failure of an equilibrium alreadycompromised".In 1968 the American National Academy of Sciences established a specialcommission in the field of geological sciences in order to study this new problem indepth. In 1972 this commission published the volume "Earth and human events".In 1971 the Russian Gerasimov and other authors pointed to some of the effectsproduced by the exploitation of natural resources in the former USSR and placedhuman impact on Nature in a historical context.In 1973 the Italian geomorphologist Panizza dedicated a chapter of his textbook"Elementi di Geomorfologia" to anthropic degradation.In 1979 Castiglioni, another Italian geomorphologist, dedicated a full chapter ofhis volume "Geomorfologia" to the forms caused or influenced by Man's activities.Still in 1978, with the work by Haigh, Anthropic Geomorphology is rightlyrecognised as a branch of Geomorphology. In the last few decades various authorsfrom different countries have dealt with anthropic geomorphology; among themworthy of note are: Gregory & Walling (1979); Goudie (1981); Drew (1983); Neboit(1983); Nir (1983).The environment is a natural system which has reached a delicate balance overa long period of time; this system works according to complex and interdependentmechanisms which have not yet been fully understood. Man is not outside nor is heabove Nature. What makes him different from the other living creatures is free will,i.e., his capability of choosing, which consists in behaviour and responsibilities notso much towards the outer world but rather towards himself, since it is Man himself,with his history, who started environmental problems. From this fact a complexity ofrelationships between knowledge and economics, development and technology,

199progress and conservation is derived.The identification and, above all, the evaluation of changes brought about by Manon the physical environment is an operation which is more complex than it mightseem at first. In this kind of study one fact is certain: the changes which haveaffected the environment as a consequence of Man's activities during this century arefar more widespread and radical than those occurring during the previous thousandyears of human presence on Earth.It is not easy to distinguish and separate ''natural" forms from ''artificiaf ones.There is a law governing reciprocal actions and the unity of geographical actionsaccording to which it is not possible to consider facts and phenomena separately. Thevarious components of Earth's surface are to be considered not according to unilateralrelations but as reciprocal and complex. There is an action of the physical environmenton Man and a reaction of Man towards the environment (Fig. 89). Moreover,it should be remembered that Man's influence on morphogenesis cannot be easilyexemplified since it cannot be reduced to a simple acceleration of natural dynamics.In some cases Man's settlements and activities can cause the worsening of erosionalprocesses in an unstable environment, such as mountainous areas, where the extremesof the climate are accompanied by high slope gradients. In other cases the works ofMan can cause disarrangements in an otherwise stable environment. This happens,for example, in tropical regions, where the destruction of rain forests and savannahshas given rise to new forces, associated with very intense rainfall, forces which wereFig. 89. Example of reciprocal relationships between Man and the environment: the village of NamcheBazar (Himalaya) was built within a glacial cirque modelled by man-made terraces (photo M. Panizza,March 1975).

200once mitigated by the thick tree canopies. In this case, more than an acceleration oferosion, the introduction of a new, more aggressive morphogenetic system isproduced which is founded on a different hierarchy of the phenomena involved(Neboit, 1983).The analysis of anthropic activities cannot take into account only "what" Man hasdone but also "how" and for "how long", since human action is discontinuous inspace, in time and in intensity. Moreover, it cannot leave out of consideration thesocial context and the historical dimension within which it took place (Neboit, 1983).A correct assessment of Man-induced morphological effects becomes possibleonly by means of a systematic study carried out according to the following procedure(Nir, 1983):— historical approach, in order to identify Man's interventions on landforms;— geomorphological approach, in order to assess the amount and extension of thegeomorphological processes observed;— socioeconomic approach, in order to investigate the dynamicity of humanactivities by considering economic and social-structural parameters; and— planning approach, in order to unite and integrate the various points of view.Also the mental attitude of whoever is going to evaluate the interactions betweenMan and the environment is a fundamental aspect to be considered. In fact, from aposition of submission to Nature, which is typical of preindustrial societies andpioneer settlement areas, Man can pass through a vision of harmony with Nature, inwhich human systems occupy a well defined place in the natural order, andeventually develop a concept of dominance over Nature, operating in the firm beliefthat artificial interventions can enhance economic and social benefits.A final consideration should be made about the planetary level of this problem:only a clear picture of the facts and interventions on a worldwide scale can lead tosome solutions. This is particularly true today, since industrial society has involvedthe whole planet, with all its physical and social realities.4.2 Man's activities and their geomorphological consequences4.2.1 General aspectsMan's interventions take place essentially on that thin layer of the Earth's surfacewhich makes up the interface between atmosphere and lithosphere where most energyexchanges and complex phenomena take place. Hardly ever are these phenomenaconfinable within preconstituted and rigid schemes, but they can nevertheless besummarised as follows (Castiglioni, 1979):— artificial forms, directly modelled by Man's activities;— works aiming to divert, correct or upgrade natural processes;— modifications of natural phenomena, indirectly resulting from Man's activities.The intensity and extension of these activities depend upon four factors:— demographic, that is the numerical consistency of the individuals practicing any

201activity which is reflected on natural dynamics;— historical: length of time of human presence and activity;— technological and cultural: capacity to exploit the environment according to one'sown purposes;— socioeconomic: demand for better living conditions and consumer goods.It may be useful to remember that Man appeared in East Africa about three millionyears ago, probably in Tanzania, Kenya and Ethiopia. His presence in Europe goesback to some one and a half million years ago, whilst his arrival in the British Islesand Japan took place much later. Australia and North America were probablyinhabited up to 30,000 years ago. After the expansion of the agricultural revolution(some 10,000 years ago), a considerable increase of the population occurred whichcan be assessed as about 200 million people by the time of Christ and to 500 millionaround the year 1650. Subsequently, the industrial revolution and the developmentof science and technology, especially of medicine and related disciplines, togetherwith the colonisation of new lands led to a real explosion of the population whichreached 1,000 million in the mid nineteenth century, 2,000 million at the beginningof the twentienth century and has at present exceeded 5,000 million people.It is obvious that the great increase of anthropic density, together with thedevelopment of culture and technology, is the main cause of the transformations ofnatural environments.The historical order of the effects of Man's intervention on the physical world canbe schematised as follows:— consequences of hunting;— consequences of animal-farming;— consequences of agriculture;— consequences of natural resources exploitation:— consequences of engineering works.The characteristics of these activities and their main consequences on the environment,even when negative, are here discussed (Piacente, in Panizza, 1988).4.2.2 Consequences of huntingThis human activity, which can with no doubt be reputed the most ancient, iscertainly the least disturbing with respect to the physical aspects of the environment.It was the first activity enterprised by Man for his survival and has always beenpresent in the history of mankind as food resource, for the supply of clothes andornamental materials and as a sport.From the geomorphological standpoint it may imply the deforestation of someareas in order to create clearings and hunting trails. It can cause limited soil creepingas a consequence of periodical or continuous passage along slopes; nevertheless, ifit is properly managed, this activity can contribute to the conservation or theupgrading of areas in precarious conditions of stability.

2024.2.3 Consequences of animal-farmingNot only is the breeding and farming of domestic animals one of the earliest ofMan's activities but also one of the most persistent anthropic actions. It wasintroduced some 10,000 years ago, when the forced concentration of animals andpeople in oases and along watercourses accustomed them to live in symbiosis: thusthe domestication of animals began and therefore the practice of breeding them.Apart from the destruction of the original vegetation, obtained by means of fireand wood cutting, the activity of animal-farming implies: the fertilising and irrigationof soil, in order to favour the growth of grass and the removal of stones, so as tomake the transit of animals easier. Nevertheless, the real problem is not so muchanimal-farming but rather overfarming, i.e., the excessive concentration of animalsper surface unit. One of the most serious effects of overfarming is the change in thepedological profile: a soil's "A" horizon, degraded and enriched in manure, is subjectto changes in its composition and structure. The repeated and regular action ofanimals' hooves causes not only soil compaction and therefore the decrease of itspermeability, but also the soil's continuous mobilisation which can eventually leadfirst to the detachment, and the destruction after, of the tree cover thus triggeringwidespread soil creep (Fig. 90).What happened in the Sahel during the severe drought of 1970 can be quoted asan example. The concentration of people around large cities, with the consequentincrease of animal-farming in these areas, led to the degradation of herbage and tothe consequent disappearance of edible species and proliferation of weeds. Moreover,Fig. 90. Creep phenomena due to over-grazing in Ra Stua (Cortina d'Ampezzo, Dolomites. Italy) (photoM. Panizza, July 1995).

203the use of wood-bearing plants including their roots as fuel caused the progressivedrying up of the vegetation around towns and villages, leaving portions of bare soilwhich would be easily removed by the actions of water and wind.4.2.4 Consequences of agricultureThe alteration or destruction of the natural vegetation in order to plant other, moreuseful species doubtlessly causes chemical, biological and physical modifications ofthe soil, as well as microclimatic changes. In fact natural vegetation, which representsthe biological answer to the totality of the environmental parameters - soil, climateand morphology - absorbs a greater quantity of morphogenetic energy than theartificial vegetation. Indeed, the latter favours the effectiveness of the degradationprocesses, with even greater effects with those types of farming practices whichperiodically leave the soil bare (Fig. 91).The degradability of cultivated lands is favoured by monoculture which is typicalof latifundism. This practice is based on periods of absence of the vegetation on largeslope portions, thus favouring the areal development and the articulation ofdegradation processes. Instead with the introduction of polyculture, where eachallotment was worked by a single owner, it was possible to produce a greater varietyof crops, with nonsimultaneous periods of absence of vegetation cover.In countries with ancient rural civilisation. Man introduced measures of mitigationof erosional phenomena such as terracing, which makes farming operations easier.Along watercourses running in plain areas, it has been a long practice, especiallyFig. 91. Example of rapid tendency toward deserification following a long drought period (1970) andintense soil exploitation (east of Dakar, Senegal) (photo M. Panizza, May 1984).

204in Europe, to cultivate crops in the outer portions of riverbeds. In this way a reductionof the flow section is determined and as a consequence runoff takes place athigher velocity and with an increased erosive power during high-water periods.In the history of agriculture there have been at least six great technologicalinnovations which by causing remarkable increases of the soil's productivity havealso implied evident interferences in the soil's natural dynamics. The first one wasirrigation, already applied 6,000 years ago in the plain of the rivers Tigris andEuphrates; the second one was the use of animals for working the land; the third onewas the exchange of farming products between the old and the new world; the fourthone was the invention of the internal combustion engine, the fifth one was given byfertilisers and the sixth one by chemical pesticides (Orr, Roberts & Lansford, 1981).Irrigation, obtained by means of artificial draining, induced great changes in thehydrographic network which can be summarised as follows: regulation of thewatercourse flow rates obtainable by means of new hydric elements such asfloodways and reservoirs; augmentation of sedimentation processes with consequentraising of the soil level and increase of evaporation; storing of water stocks withrelative interference in the sedimentation, current flow and erosion patterns; changesin the flow rate owing to the construction of dams; alterations of the dynamicequilibrium following the construction of harbours and moles. Moreover, irrigationmay induce microclimatic changes, especially in the rate of humidity. Canal anddrainage systems have influenced the alluvial plain landscapes in many countries like,for example, England and Italy.The use of animal work for ploughing has intensified the exploitation of slopes.The consequences of ploughing depend on the angle between furrow and slopedirections. Vertical ploughing, from the slope top to the toe, is the most simplemethod but also the most hazardous, especially if hydric circulation has not beenconsidered. Furrows can in fact evolve into concentrated runoff streams. Furthermore,on mostly clayey slopes the practice of ploughing transversally to the gradient,according to the contour lines, could favour water stagnation, absorption, percolationand plasticisation phenomena with consequent hazard conditions owing to solifluctionor earth flows.The exchange of farming products between the old and the new world has notinduced particular geomorphological phenomena, apart from those cases where aradical conversion in farming methods was introduced with considerable alterationsalong the slopes.The introduction of mechanical machinery has implied a more intense exploitationof farming lands: tractors and disk-ploughs have contributed to triggering moremarked erosive phenomena. The ploughshare towed by oxen goes down into the soilat the most 15 cm, whilst mechanical ploughing can create furrows up to 50—60 cmin depth. Moreover, since mechanical machines require much more space for theirmovements, many shrubs and hedgerows have been destroyed, thus increasing erosiveprocesses.The use of chemical fertilisers and pesticides can alter the soils' pedologicalcharacteristics to a certain depth with consequences also for morphogenetic processes.

205Nevertheless, there are also some positive effects of farming on the environment:the systematic conservation and re-establishment of farming soils along slopesmay improve the defence against erosion, as well as the maintenance of paths andcart-roads, the conservation of clearings inside woods, the management of hydricsystems, etc.4.2.5 Consequences of resource exploitationThe rise of the world population and the consequent increase of needs is thefundamental element which has created an enormous increment of resourceexploitation. The consequent need to satisfy the ever-increasing demand for naturalresources inevitably determines several environmental problems. For example, theincreased density of people, houses, industrial plants and transport infrastructuresintensify the production of pollutants released in the air, water and soil. Moreover,the construction of buildings, underground structures, communication routes, sportand leisure facilities and the dumping of waste materials and garbage in certain areascould cause the destruction of the vegetation and create conditions predisposingaccelerated erosion and mass movements. The drawing of water and gas from thesubsoil for industrial and domestic purposes can cause lowering of the water table orland subsidence and increase the hazard of aquifer pollution.The century-old struggle of Man for the exploitation of natural resources hasalways been accompanied by the search for instruments and forces capable ofenhancing his capacity of carrying out works. For an extremely long time thispossibility was guaranteed by the physical work of Man himself and of the animalsthat he was progressively domesticating. The prime source of energy was food,provided for both Man and animals by the vegetables, which are the only livingbeings capable of absorbing energy by exploiting directly the Sun's heat and light.Subsequently, great discoveries such as fire, the wheel, the lever, the arch, the pulley,etc. enhanced and made Man's and animals' work easier.An important stage in the history of human work was the capacity to utilise greatand small physical forces found in the environment, such as wind and the movementof water in rivers. Subsequently, the history of mankind progress was more and moremarked by the discovery of steam and fuel engines capable of reducing energy wasteand increasing work production. The discovery and later use of fossil fuels, likenatural gas and oil which could produce caloric powers much superior to coal's, wasa major step forward. Even more important was the discovery that all bodies possessenormous energy powers at an atomic level. Today's world often considers withperplexity and fear this energy source, which probably Man is not yet capable ofknowing and controlling. Notwithstanding this, the experience and studies still inprogress point to the fact that atomic power may be one of the most effectivesolutions for our energy needs.Similarly, also the discussion on the research and exploitation of the so called"powers at nil risk" is particularly heated. Hydroelectric power plants, solar panels,wind mills and tide power plants are the most interesting alternative solutions. It

206should nevertheless be emphasized that these so called ''mild powers" show twoconsiderable drawbacks: the first is the poor energy yield and the second the highcost necessary for their generalised exploitation, at least at the present state of the art.The problem concerning the progressive depletion of traditional energy sourceshas triggered a confrontation, and sometimes a clash, between two oppositetendencies of thought. According to some people, if the present rhythm of developmentis maintained the complete exhaustion of energy reserves will soon be reached:in these conditions, if a catastrophe is to be avoided the only solution is to return toa preindustrial situation. This is the position of some ecologists, at least the mostradical ones, according to whom technological development is a synonym ofenvironmental catastrophism. On the contrary, according to others, mankind willmanage to solve its own problems of growth and development by means of studiesand investigations producing new technological conquests, as has already happenedseveral times in history.Human welfare and mining and energy resources in general have always been sointertwined that the various stages of Man's history were named after the mostavailable minerals: stone, bronze and iron ages. Notwithstanding the progressivedepletion of the richest ore deposits, the constant improvements of exploitationtechnologies have allowed the quarrying of ever increasing amounts of raw materialsto be carried out at more and more competitive prices. Nevertheless, the mainproblem is not so much given by the progressive dwindling of the available materialsbut rather by the high human and environmental costs resulting from intense andconstant exploitation. Destruction of the original landscape, slope instability, river andgroundwater pollution are the most serious impacts of Man's misuse of the naturalresources. At this stage, the negative effects of Man's activities spread over larger andlarger areas threaten to exceed the direct benefits. In particular, the mining industrycontributes to the atmospheric heating and pollution since it is one of the mainconsumers of power.The extraction of minerals causes particularly serious environmental consequencesin developing countries since most of the world's ore deposits are concentrated there.It should be pointed out that with the term '^minerals" a great variety of raw materialsdirectly extracted from the soil and subsoil is meant, including: metals such asaluminium, iron, copper; substances for industrial use such as lime, sodium carbonate;lithic materials such as sand, gravel and energy-producing elements such as uranium,or compounds such as coal and liquid and gaseous hydrocarbons.If the excavation of mineral resources continued at present rhythms, theenvironmental consequences would be devastating. Between 1750 and 1900 theconsumption of minerals doubled, whilst from 1900 to the present day the increasehas been 10-fold. It should furthermore be pointed out that today new materials haveappeared, such as plastics, ceramics and high technology compounds, which competewith metals. As a consequence, the consumption of minerals is growing more rapidlyin developing countries than in industrialised ones.The mining and working of ore deposits has created in many countries vastdegraded areas. Environmental damage is caused by several factors such as: site

207morphology, amount of quarried material, depth and extension of ore deposit,chemical composition of the extracted material and of the surrounding soil and rock,techniques used for quarrying and working the material, management and disposal oftailings and rock waste. A significant example of this is offered by the Pangunacopper mine, in Papua New Guinea, which dumped 600 million tons of contaminatedmetal waste into the Kawerong river.It has been calculated that each year the digging out of noncombustible materialsfrom the subsoil causes damage to half a million hectares of land. This sort ofdamage is often irreversible, at least on a human life scale, as witnessed by thedramatic changes in the Bolivian landscape after over 500 years of mining activities.The geological and, in particular, geomorphological problems linked to theexploitation of natural resources are innumerable. As an example, the various miningactivities carried out on the Earth's surface can be quoted. Whether rock materials orsoils are involved, quarrying activities always have considerable impact on theoriginal relief, since they imply changes in surface morphology, with digging out ofmaterial from one area and its accumulation in another. In the last hundred years thenumber and extent of these interventions have multiplied, especially since theintroduction of more and more powerful mechanical machines for earth movements.As material is excavated there is an inevitable accumulation of waste which oftenmakes up real "man-made reliefs". Also garbage heaps, tipping areas and otherindustrial refuse make up semipervious surfaces which compromise both the drainagepatterns and the potability of water.An example of irreversible environmental degradation is given by the consequencesof quarrying activities in riverbeds (see 2.1.2).Moreover, the negative effects are not limited to the exploitation period but canpersist and in some cases worsen if the quarrying area is abandoned without adequateupgrading operations for proper reuse. Slope stability problems arise not only in thequarrying areas but also in the heaps of accumulated waste materials. Also cases ofsoil and water pollution occur if quarries or soil pits are utilised as uncontrolleddumping sites. These human activities can also cause the alteration or destruction ofgeomorphological assets (impact).4.2.6 Consequences of engineering worksThese consist in the construction of roads, bridges, dams, buildings, reservoirs,hydraulic works, dumping sites, harbours and coastal structures, tourist facilities, etc.Changes usually occur in the hydrographic network together with floods, landslides,slope instability, reduction of soil permeability, microclimatic variations, air, waterand soil pollution, etc. (Fig. 92).One of the first changes brought about in the environment by the construction ofroads, houses and other artificial structures is the transformation of natural andfarming terrain into urban soil. In geomorphological terms, Man's activity in urbanareas determines the interruption of natural processes governing the formation of soilsand the introduction of a new ''anthropic soil" made up of asphalted areas, gardens

208Fig. 92. Phenomena of intense erosion along the banks of an artificial lake formed after the constructionof a dam near Torun (Poland) (photo M. Panizza, October 1970).and various kinds of constructions (Nir, 1983). Urban development is indeedcharacterised by the sealing up of natural soil with the formation of impermeablesurfaces. Urban soil is subjected to totally artificial drainage, with a higher densitythan natural drainage. In urban areas water percolation is much reduced, resulting ina higher flood hazard.In 1850 only 50 towns worldwide had more than 100,000 inhabitants, whereasonly three had more than 1,000,000 people. In 1973 over 1,000 towns had more than100,000 inhabitants and nearly 200 more than 1,000,000 dwellers.Also the construction of airports and harbours causes widespread changes in waterdrainage systems, especially regarding the vast extent of the surfaces involved.Slope cutting for road and other constructions always determines variations instability conditions and in groundwater flow patterns, with waterfall effects in areasupstream of the cutting, greater production of detrital materials downslope,destruction of the vegetation, etc.Intense tourist and sport development of high mountain areas has introducedanother disturbing effect, thus compromising the already difficult balance of theseareas even further with the felling of trees in order to create ski pistes, cableways andski lifts. It is not so much the modest extension of deforested areas that can decreaseslope stability but rather the fact that these wood cutting activities are mostlyperpendicular to the valley floor and rather inclined, thus favouring the concentratedflow of surface water and the formation of avalanches.

209Hydraulic works can produce important changes in the natural evolution of rivers,mainly by reducing the intake and transport of debris to the sea. For example, riverbarriers, besides modifying the water runoff trend, are very effective traps for solidmatter. Moreover, in order to mitigate the devastating effects of floods, a retentionof debris which otherwise would have reached the sea is carried out by means ofconstructing flow-control weirs and basins with free overfall and reclaiming marshyareas in some alluvial plains.Man's action along sea coasts can become particularly detrimental (impact). Alsoin Italy, since the beginning of this century, the excavation of loose materials fromsand dunes, frontshores and beaches, which make up three indissoluble elements ofthe same system, has been carried out in a disorderly manner, with neither planningnor control. In this way, an already precarious natural equilibrium, where easilyerodable and transportable materials are subject to the action of high-energy agentsuch as wave motion, was further compromised. The demolition of dunes, precioussand deposits defending the inland territory and giving consistency to coasdines, hasproduced damage which is mostly irreparable. The construction of roads alongbeaches can cause disastrous effects: once the beach has been deprived of its upperportion its profile undergoes an alteration. Moreover, vertical walls hit by breakersduring sea storms exacerbate the turbulence of backwash, increasing the drawing ofmaterial from low beaches.Major harbour works and the construction of shipping canals interfere considerablywith the transit of material, hindering its transfer onto the beaches. Alsodumping solid waste materials offshore, such as building yard rubble, can causediversions of shore currents, with consequent depletion of material from the beach(see 3.5.2).Furthermore, urban development or any other situation characterised by highpopulation concentration, increases the possible destructive effects (risk) of naturalphenomena and the presence of an urban environment is responsible for climatechanges, with the well known consequences of an increase in the greenhouse effect.Finally, it should be pointed out that engineering works can also produce positiveeffects on the environment or exert a specific defence function from natural hazardssuch as flood controls, improve the flow of watercourses, stabilise slopes, protectcoasts. It is nevertheless indispensable to foresee with scientific exactitude all possiblerepercussions of human interventions on the environment system, lest an engineeringwork, although planned and constructed for the defence against some type of event,may have negative effects and trigger other kinds of hazard.4.3 ConclusionsIn its relationships with Man, the environment should be studied according to aglobal approach centred on the concept of a system, by considering that:— a system represents a generalisation or, rather, a model and therefore anabstraction from the real world and its complexities;

210— each system depends on the relationships existing between its variables;— the functioning of a system depends on the existence of forces and energysources;— each natural system cannot be considered as an isolated system, since both matterand energy can be transferred;— a natural system always tends to evolve. What changes the state of a system arethe processes that take place inside it;— in order to assess the energy of a system it is necessary to know not only theinitial and final states but also the intermediate ones;— the natural system is very different from the anthropic one in terms of space, timeand reactions: there are various degrees of complexity, diversity and state. Evenenvironments which seem to be stable often give this impression only becausethey have been insufficiently studied and documented.According to these definitions, the natural system is the synthesis of the naturalcontext (both physical and biological) of Man's activities (from historical heritage toartistic records, economic aspects, social conditions, etc.) and their position within acultural perspective. This means, above all, recognising a continuity between Nature,history, traditions, culture, socioeconomic activities and development prospects. Itmeans expressing the Man-Nature relationship in terms of continuous evolution andreciprocal incentives in time and space. In this way, also the dualistic view opposing"natural" and "anthropic" contexts would be overcome.Each single variable of this system, although characterised by its own functionand evolution, should therefore be considered within the framework of the functionsand dynamics of its own territory. If the evolutionary trend of the elements makingup a system is not congruent their own evolutive tendency, congruent with the wholesystem's, then these elements are as yet unbalanced, although eventually they willreach some form of equilibrium. The achievement of this equilibrium can take placeeither through slow dynamic processes easily assimilated by other elements orparticularly rapid and sudden ones with serious repercussions on all the system.Finally, another aspect should not be neglected: the factors making up a societyare given by the physical environment and its history, but society often evolvesautonomously, owing to economic and political causes. Therefore, society itselfmakes up a system, which sometimes appears to be unconnected with the mainnatural system. This extraneousness of the social system is obviously more apparentthan real and is basically due to its evolution times which hardly ever coincide withthose of the natural system.The most significant parameters of the environmental system can be schematisedas follows.Scientific — in the environmental system each element has its own specificmeaning and role in global dynamics. The knowledge of all its components is stillinsufficient; each research and result should be documented and stored for futureinvestigations.Ethical — every species has the right to live in a suitable environment.Aesthetic — each landscape form and aspect, each animal and plant is beautiful

211and significant and, as such, should be preserved with all its original prerogatives.Biodiversity — the diversity of species should be maintained and protected.Stability of the physical environment should not be compromised, since the lifeand development of the diverse living species depend on this parameter.Recreational value — the conservation and improvement of the environment is ofvalue also from the recreational and leisure point of view (excursions, parks, photosafari,etc.) and therefore has also considerable social and economic implications.Economic value — natural and biological assets can make up a considerable sourceof immediate revenue and cultural value if properly managed as resources.Heritage for future generations — This is one of the fundamental reasons forpreserving the environment and living species.The environment has a limited capacity to adjust to the ever growing changescaused by man's activities without undergoing irreversible transformations, especiallywhere Man's presence is intense and long-lasting. Indeed, in some places these limitshave already been exceeded.The study of the development-life quality ratio can be faced from two differentstandpoints: either starting from environmental management and the technologies usedfor assessing impact, or starting from analytical evaluation processes of the effectiveimpacts as they are studied in order to better define specific measures for their correctmanagement.In the past few years, the evolution of public management has brought about newsocial demands with a growing awareness of the social and environmental costs oftechnological development. A totally new phase of political commitment aiming atthe satisfaction of previously unknown social demands has begun. Therefore staticand habitual models must be overcome in order to take advantage of intercultural andpluralistic dialectic views. In this way a dichotomy has been created: on one sidescientists, economists and managers maintain that decisions should be taken accordingto rational and scientific arguments; on the other side sociologists and anthropologistssupport the idea that governments should provide political solutions taking intoaccount the conflicts between society and technology with a general and long-termview.The history of the last twenty years has been marked by scientific and socialreflections upon these problems and the conflicts created by Man's inadequacy indefining and measuring "risk", which is always rediscussed and redefined by socialprocesses directly involving the role of science. In fact, while for some risks thepolitical measures are consolidated or at least outlined, for others they are still to bedefined. Among them, the artificial transformation of the territory, the concentrationsof carbon dioxide and ozone, urban congestion, the ever growing noise andpsychological and social impacts of the urban environment should be quoted.Moreover, there is today a misleading tendency to consider the problem of risks outof its historical context, without considering what happened in the past. By directingmost of his energies towards scientific-technological and economic knowledge, Manhas not given adequate thought to the management of the problem. In such a complexworld, so full of uncertainties, where roles and responsibilities are more difficult to

212identify and past certainties are no longer valid, the crisis of self-confidence shouldbe transformed into an awareness of Man's own limits in order to promote pluralismof ideas and the search for new perspectives and models, since a culture concentratingonly on a single element impedes the understanding of changes.Man in fact is provided with a vast cultural heritage and lives in an environmentwhich is not only the result of physical, chemical and biological processes, but alsocultural and social ones.Within a context of global planning, it is therefore indispensable to find anagreement on the priority criteria for environmental management, in order to optimisethe scanty resources still available. This implies that systematic analyses must firstbe made at a global level aiming to negotiate these problems which are bound to bemore and more urgent in future. At the same time, it is necessary to develop studiesand techniques directed to the decrease or at least optimisation of energy consumption,the increase of agricultural production, support for recycling projects,reclamation of degraded territories, etc.Obviously, on an international scale environmental problems are more difficultto solve than domestic ones. There are two reasons for this: a single authority capableof formulating and applying the most opportune political measures does not exist; thepossible solutions must consider a balanced ratio between costs and advantages whichin most cases varies from one country to another. Moreover, some countries couldhave more urgent national problems to face and therefore less economic potential forintervening in international problems.When ecological degradation extends its effects beyond national boundaries orsolutions to environmental problems require interventions on an international scale,then the codification of adequate rules and norms clashes with greater difficulties.The concept of the existence of a common heritage at a planetary level wasalready recognised some time ago by several governments (for example, the treatieson Antarctica and the oceans). Nevertheless, the concept of clear common responsibilitiesin the conservation and management of natural resources is a very recentlyacquired notion.The awareness that environmental problems should be faced on a planetary scalehas given rise to institutional innovations both at a national and international level.International Organisations such as the European Union, the African UnionOrganisation and Pan-American Nations Organisation have extended their cooperationalso to environmental issues. Moreover, several specialised public and nongovernmentalagencies and associations are involved in problems concerning the environmentin a broad sense: sea pollution, management of nuclear and toxic waste, protectionof species in danger of extinction, conservation of historical monuments, etc.There are three great categories of issues which require international solutions:1) When resources are shared between different countries (for example, a watercourseor a sea).2) When certain resources, although belonging to a single country, represent a valuefor the world community (for example, the rain forests or the various habitats ofparticular species).

2133) Other environmental resources cannot be divided according to a national criterionsince they are a common asset for all mankind (for example, the atmosphere orthe oceans).One of the most representative examples is that of international watercourses whichhave become the object of negotiation between most European countries and NorthAmerican. Over 40% of the world population lives in fluvial basins interesting morethan one nation. Although international legislation is still insufficient on this issue,two basic principles have been established by international organisations: eachcountry has the clear obligation not to cause serious damage to the countries withwhich it shares the watercourse; the rights on the waters must be equally dividedbetween the partner states. An example of successful agreement, achieved in 1960with the help of the World Bank, is that relative to the River Indus catchment basin,equally shared between India and Pakistan.Among various difficulties, the different prospects of developed and developingcountries should not be underestimated.The former are undergoing a qualitative transformation of consumer goods, dueto the substantial stability of the population and saturation with primary goods: inthese conditions a decrease in environmental stress can be foreseen for the nearfuture. Moreover, great technological development offers technologies which are morecompatible with respect for the environment. Last but not least, the growingawareness of public opinion towards environmental problems.In developing countries, however, the population continues to grow with theprospect of doubling in the next 50 years (e.g. Asia). An urgent increase in theproduction of fundamental goods is therefore required since in most of these countriesthe standard of living is at the limit of survival. In these cases the protection of theenvironment is no longer the main issue but, on the contrary, is considered as ahindrance to the development of agricultural and industrial production. All this isaccompanied by obstacles presented by the inadequacy of infrastructures, tooexpensive depuration technologies and strong cultural and social barriers.In order to achieve positive results, the problem should be faced through constantdialogue between scientists and politicians and also through the indispensableinvolvement of public opinion, by means of information and education programmes.Another aspect should also be emphasized: if on the one hand Man uses andmodels the Earth's surface, on the other hand he is becoming more and morevulnerable to natural phenomena: floods, landslides, volcanic eruptions, earthquakeswhich in the past had only a local effect, now hold worldwide dimensions since allsocial realities are linked by strictly interdependent economic, energy and communicationsystems.Although it is now undoubtedly certain that Man's presence and actions havenegative repercussions on the environment, nevertheless there is no need to beexcessively alarmed. Some remarkable changes that Man has brought about in Earth'snatural phenomena, behaving like a real geological agent, are neither sudden norrecent, but they are rather the cumulative product of different practices carried outover a long period of time. Since the effects of Man's activities on the environment

214in the near future are not totally foreseeable, the present challenge consists inassessing correctly not only the "how" and "how much" of human actions but ratherthe capacity for assimilation and reaction of the whole natural system. It should beremembered, in fact, that the natural system has its own dynamism within such vasttemporal and spatial dimensions that Man's activities often exert effects whoseimportance is only apparent.Nonprofessional simplifications, preconstituted schemes and superficial mediainformation are unfortunately more and more frequent. This kind of approach shouldbe avoided as it brings about bewilderment and confusion in public opinion, creatingobstacles for a correct attitude to environmental issues. The environment systemshould therefore be analysed with scientific exactitude in all its components andinteractions, so that each intervention of Man can take into account all possiblerepercussions and consequences once they have been properly assessed.5 VULNERABILITY AND GEOMORPHOLOGICAL RISK5.1 Vulnerability to hazardWith reference to the subject defined in section 1.6 and considering natural risk ingeneral, it is possible to state that the severity of the risk depends on the hazarddegree, the vulnerability degree and the relationship between them. It was shown howa territory's vulnerability is given by the concurrence of various components (Fig.93): exposure, economy, planning and social organisation. It is not within the author'scompetence nor within the goals of this volume to provide a specific discussion onthe sectors concerning engineering, economics, political and social sciences orwhatever could be included in the definition of vulnerability.Nevertheless, for some of the components shown in Fig. 93, it was consideredopportune to show in any case the main aspects of the relationships with hazards: thisis the case of exposure, economy and planning. Among the other topics that can beof more interest to a geomorphologist, environmental education, which is includedin social organisation, was dealt with in most detail (see 5.4). This interest is of twokinds: the first is directly professional and involves teachers, researchers andtechnicians, the second, on the other hand, concerns the social role that anyExposureEconomyVULNERABILITY

215lowexposureVULNERABILITYhighFig. 94. Scheme of risk severity in relation with vulnerabiUty exposure and hazard probabihty.environment operator could and should assume not only in the contingent riskmoments, but especially in the daily practice of a territory's use and management.As for exposure. Fig. 94 connects this vulnerability component to the probabilityof a hazard's occurrence. With reference to the definition given in section 1.4, ahazard is seen to be linked to the probability of its occurrence in time, as well as itsmagnitude. It is obvious that the higher the hazard and vulnerability values, thehigher will also be the severity of the risk. Moreover, if the value of one of the twofactors is low, as a consequence, the severity of the risk is relatively low: like, forexample, a low-vulnerability area like a desert related to a high landslide hazard, oran area with low landslide hazard, like a plain, related to a highly populated area. Inboth cases the geomorphological risk connected with landslides will be relatively low.Again in the case of exposure, considered as a component of vulnerability, acertain scale of values is taken into account. In the first place human life is found,including as a consequence in terms of risk not only the death of people but also anykind of injury, disease and stress. At a lower level of vulnerability the aspect ofgoods can be considered, with its consequences of property damage and economic

216loss that a particular hazard can cause: in this case not only is the way of constructingbuildings, structures and infrastructures of fundamental importance, that is, thetypes of construction and the materials used, but it is also essential to consider wherethese works are constructed, for example, in situations of geomorphologicalinstability.Exposure to vulnerability is considered also with regard to the environment,including both biological (fauna and flora) and abiological components (for example,geomorphological assets: see 2.2) since they can both undergo destruction or damage.As regards another component of vulnerability, i.e., the economy, the highervulnerability of industrial areas has already been pointed out: factories, infrastructuralbuildings, communication routes, etc., can receive considerable material damage whena hazard occurs. Furthermore, a concentration of workers, employees, students, etc.makes the percentage of human lives that can be lost or injured even higher. On thecontrary, in farming areas the risks concerning material damage or loss of humanlives are generally more limited.As for planning, the development of new housing, new activities and newinfrastructures, as well as the expansion of existing ones, should take into account thevulnerability degree of the new constructions and settlements, relating them with thetype, frequency and magnitude of the geomorphological hazards; that is, their riskshould be properly assessed. The population increase and greater leisure time giverise to more and more unregulated urban developments, the construction of secondhomes and the pursuit of recreational facilities. The increasing need for land leads tothe development of previously avoided hazard-prone areas or of coasts and mountainswhich are potentially more hazardous. Therefore, the evaluation and detailed zonationof the potential hazard zone are indispensable for adequate planning policy, togetherwith the application of rigorous norms and restrictions on construction activities.Unfortunately such rulings always appear to be in contrast with the ever increasingcompetition for land and with commercial interests, and are therefore difficult toapply.Vulnerability should also be considered in relation to the degree of socialorganisation present, i.e., environmental education, civil defence, and prediction andmonitoring techniques. Where people know and safeguard their territory, where thebodies governing intervention are efficient, and where advanced warning systems ofmajor instabihties exist (e.g., river-spates, sea storms etc.) and finally, where such alevel of social organisation is high, there will certainly be lower levels of vulnerability.5.2 Risk mitigationAs previously said, risk mitigation can be achieved either by reducing the hazard orby reducing vulnerability (Fig. 95).As regards geomorphological hazard reduction, there are two possibilities: processmodification or hazard resistance.

217RISKmitigationLiA-TADf^ J i.- process modificationHAZARD reduction[ hazards resistance (active protection)% /... K .r-r^ A r^M .-xX . structural measures (passive protection)VULNERABILITY reduction v^ K /[ prediction, forecastFig. 95. Scheme of risk mitigation.In the case of process modification, action should be taken regarding the causesof the geomorphological phenomenon: for example, in a process of solifluction waterpercolation into the ground could be eliminated; or in a process of stream erosion thewater velocity could be reduced. Nevertheless, with some causes, such as those of ameteorological nature, it is difficult to intervene, considering the present stage of eventhe most sophisticated technologies.In the case of hazard resistance, it is opportune to prearrange particular measuresto protect the environment subject to a geomorphological process: for example, thelocation and resetting of vegetative ground cover against soil erosion; or theconstruction of defence works against bank erosion, such as lateral walls built alongriversides. This type of hazard reduction can also be defined as ''active protection"against the risk. Nevertheless, when some kinds of geomorphological hazards are tobe faced, like certain mass movements, it seems difficult to find effective countermeasures,unless very high economic costs are accepted which in some cases mightnot be justified by the intervention works planned.Proceeding now to vulnerability reduction, with reference to exposure, there aretwo possible choices (Fig. 95): structural measures or prediction and forecast.Structural measures can be defined as "passive protection" against the risk: thatis, specific construction norms for buildings, infrastructures, etc. should be adoptedin areas considered as subject to some form of geomorphological instability. Thesespecific engineering measures are applied considering for each case the entity andtype of hazard as well as the expected lifetime of the structure. Nevertheless, thispassive protection can hardly be comprehensive. In any case, the assessment of themagnitude and probability of the hazard and the evaluation of costs and benefits willallow the entity of the risk to be identified. As previously stated in section L6, it willbe possible to choose the guarantees and the levels of protection which means makinga political choice: the higher the risk threshold adopted, the more onerous andexpensive it will be.As previously underlined, another way to reduce vulnerability is offered by thepossibility to predict and forecast a geomorphological hazard. By means of theseoperations, risk mitigation is assuming more and more importance and a greaterlikelihood of results thanks to scientific and technological advances. An example isgiven by weather forecast, increasingly facilitated by remote sensing communicationsand computer elaborations. Another example can refer to mass movements which canbe identified by means of monitoring systems and anticipated by simulation modelsof the geomorphological process.

2185.3 Prediction and forecastIt is important to define the terms "prediction" and "forecasting" and to point out thedifferences. In Uterature there are numerous, more or less analogous definitions,among which the most recent are given by Flageollet (1989), concerning the mostspecific geomorphological aspects, and by Smith (1992), concerning more generalenvironmental aspects. For other definitions the bibliography quoted by the abovementioned authors may be referred to.The term prediction shows the probability of recurrence in a certain area of anevent which has already occurred. It is based on statistical methods derived fromhistorical data, catalogues, long-term monitoring operations, etc. Predictions areusually long-termed and can be both regional (e.g., earthquake-related landslides ormeteorological events) and local (for example, the amount of erosion on a slope oralong a watercourse). As for the recurrence of geomorphological events, for some ofthem (e.g., landslides) it is sometimes possible to establish the temporal occurrenceof the phenomena and therefore a prediction, especially on regional terms (see Casaleet al., eds., 1994). In other cases, such as those connected with man's activities, it ismuch more difficult to make predictions, unless regular and repetitive actions aretaken into account (e.g., the systematic exploitation of a natural resource).The term forecast refers on the contrary to an indication of the timing, locationand magnitude of an impending hazard. Forecasting can therefore take place only ona precise site and requires a detailed knowledge of the phenomenon, especially bymeans of monitoring systems. Specific examples are illustrated by Gasparetto et al.(1994) and Mantovani et al. (1994) for some landslides in the Eastern Dolomites. Insome cases, in connection with the monitoring systems for hazard forecasting, thereis also an "alarm system" which alerts the public of an impending risk. An exampleof an alarm system is offered by Fig. 96 showing the Tessina landslide, in the EasternDolomites.For the study, prediction and forecasting of natural hazards, including geomorphologicalones, simulation models are often applied. They are a simplification andscale reduction of a phenomenon and are used with ever increasing frequency thanksto the development of instrumentation and the use of computers. The models that aremost frequently used in Geomorphology are essentially of two types: physical andmathematical.Physical models are based on the laboratory reproduction of the physicalcharacteristics of the phenomena studied: for example, the lithological, slope-angle,meteorological, etc. characteristics of a landslide are reproduced in scale in order toassess the evolution of a prototype and transfer the results to the real case.Mathematical or digital models make use of a computer receiving a certainnumber of data inserted by means of prearranged or specifically developedprogrammes and elaborated in order to simulate a natural phenomenon. These modelscan be applied though only in limited situations and there are elements of uncertaintyconnected with the problems of modelling the geomorphological process itself, ofensuring the correct representation of the choice of model assumption, of the weight

219P4 P^ E2'LAMOSANOSTATION1 CITY HALLLAMOSANO-4 -££fj0MODEMVIDEO EECi—[m^FIREMENBELLUNOPI,..., P5: directional barsEl, E2: echometersC1, ..., C3: video camerasWl, W2: extensometers in seriesTD: automatic topographic systemFig. 96. The Tessina landslide alarm system (Belluno, Italy).to be given to all different data categories, of the simulation of time, magnitude andfrequency factors, etc. Mathematical models can be subdivided into deterministic,probabilistic and optimization models (Anderson ed, 1988).For a more detailed knowledge on these subjects the following articles areadvised: Brundsen (1980), Thornes (1983), Woldenberg ed. (1985), Anderson ed.(1988) as well as those quoted in them.5.4 Environmental education**by Sandra PIACENTEIn recent years there has been considerable progress and advance in scientific andtechnological knowledge together with a growing interest and, in particular, anemotional involvement of public opinion. This has not been supported, however, byan adequate level of general education or by suitable educational strategies aimed atthe general public.This situation is rooted in a rapidly and radically changing reality, mainly causedby man's impact on the environment, which has not been followed by properdevelopment plans and environmental education programming. Indeed, the presentsituation shows that the knowledge of natural phenomena is generally inaccurate andscattered.

220The knowledge of the Earth's evolution and dynamics are lacking at all levels:social, political, economic and educational. No effort is made to give a carefulanalysis of physical reality but, on the contrary, there is a dangerous tendency toimprovise and elaborate partial and superficial notions on phenomena related toparticularly catastrophic events, without pursuing a correct understanding of thecauses and processes determining the phenomena and considering only the mostevident aspects, which are certainly not the only ones.It is now evident that any strategy of intervention involving the natural environmentbecomes feasible only through a radical change of people's mentality. Thegeneral attitude of interpreting and using the surrounding environment according toone's personal needs should therefore change: this implies a participation and anindependent ability to assess a situation which can be achieved only by means of anadequate and correct knowledge of the problems. This should take place with theconviction that knowing and learning compel people to assume a different mentalattitude, i.e., an active role with respect to the environment in which they live,showing the way towards a new way of making, receiving and transmitting culturalvalues.The concept of evolution, i.e., the continuous dynamism of any natural system,is fundamental to any knowledge of the environment. A dynamic approach to thisstudy can be correctly achieved at various, even extremely elementary levels, bybreaking down a system into its basic components.In this way the knowledge of the real world will no longer be based only onsuperficial and factual data but will give the necessary importance to the continuouschanges which often exert decisive influence on our lives, our culture, our economyas well as conditioning our future.The actual environment should be considered as the result of relations betweennatural and human elements, which can be ascribed to simple and complete systemswhose variables have contributed to transform the Earth. The correct attitude to theenvironment means developing research which is historically-based in the widestpossible sense, since this will allow the individuation of the disturbing factors whichin various epochs interrupted the balance of this system forcing other elements toadapt. A disturbing factor, which often seems exceptional, when occurring in asudden and striking way, will instead appear to be neither exceptional nor perturbingafter an investigation of this type, since it will be seen that it was already presentwithin the system, especially if the environment was receptive. The knowledge andidentification of the most probable ''exceptional" events will allow them to beincluded in this system and the other elements to be prepared for coexistence.Furthermore, the actual dynamics of society should be considered because thoughit originated and evolved in the physical environment, society has developedindependently into a system which appears as external to the main system, owingessentially to political and economic factors. This extraneousness of the social systemis more apparent than real, basically because its rhythms of evolution are hardly evercomparable with those of the physical system.In any case, apart from shortcomings, inaccuracies and sensationalisms, in recent

221years all mass-media have undoubtedly contributed in divulging new knowledge andcreating a public conscience: the concern for environmental problems has becomecommonplace. This reversal of this trend of public mentality is the most noticeableand tangible result of years of images, articles, round tables and debates. Publicopinion has matured new ideas and convictions: society cannot rely any longer juston aid, voluntary service and good-hearted feelings. It should rather pursue welldefined political guidelines and prevention-type initiatives leading towards riskmitigation.Nowadays, at the end of the twentienth century, the protection of the environmentis mostly considered as dynamic conservation, i.e., to increase in value all thoseaspects that make the environment significant and unique on account of itscharacteristics, origin, history and, especially, the life and activities that take placein it. From this viewpoint each environment, even the apparently most insignificant,should have its true value properly recognised and therefore protected, since in anycase it contains original and specific features: the correct identification andknowledge of its distinctive characters are of paramount importance.This type of dynamic conservation, including all the initiatives and works capableof promoting and protecting a certain environment in order to make it directlyaccessible to the general public, should necessarily be put into practice by means offorms of knowledge and multiple management. Indeed, only through the understandingof its past, even the most remote one (such as its geological history), of itsevolution mechanisms and equilibria, is it possible to identify those aspects andvalues, often unknown or forgotten, neglected or damaged, capable of providingcorrect elements for assessment and planning. Therefore the outcome is the definitionof natural assets (such as geomorphological assets). If these are properly identifiedand understood, they are no longer seen from a merely aesthetic or spectacular pointof view, nor do they belong only to the narrow field of scientific knowledge, butbecome a stable cultural heritage, an integral part of the formation and therefore ofthe education of all those that benefit from these assets.Knowledge is the basis on which a rational framework can be built in order tocreate a policy of correct use of the environment, i.e., conservation and improvement,with appropriate interventions both for protection and at a cultural, promotional,social, touristic and economic level. However, such integrated planning should notbe limited to emphasizing acquired knowledge and expertise, but should aim at adeeper study of ideas previously just guessed at, preferably using local forces andresources, involving both young and old in a responsible role: the former in theeducational and professional phases, the latter in the conservation and transmissionof knowledge and values by recalling the past to prepare for the future.Of course each operation of cognitive research already has an intrinsic value,independently of any possible use that could be made of it, but in the case ofenvironmental and cultural assets, knowledge nearly always triggers operativeproposals which often promote ideas and opinions, and thus assume considerableeducational significance.In the past few years the demand for knowledge regarding conservation and the

222correct defence of Nature have become a clear social need, since people have becomeaware that these are the essential basic conditions not only for a better quality of lifebut also for the survival of the human race. Area management therefore becomes theusual field preferred for a comparison between individual and general interests,assuming that each hypothesis and research proposal should be realised not so muchfor giving immediate answers but mainly for asking the right questions correctly,which would support new ideas and incentives.A correct conception of balanced relationships between man and Nature is basedupon two essential parameters: research and information. The former is developed bymeans of integrated and coordinated studies in the different sectors of natural, humanand social sciences; the latter is developed by giving the citizen or, even better, thefuture citizen, adequate means to obtain knowledge. Indeed, the knowledge ofenvironmental dynamics is a necessary requirement for understanding the problemsresulting from equilibrium, unbalances and development and for trying to outline, atleast at a cognitive level, forecast scenarios.Naturally, such a complex and absorbing project cannot be faced in an episodicor occasional way, with the incentive, for example, of particularly disturbingphenomena (such as violent earthquakes, volcanic eruptions, landslides, floods,pollution, etc.) but should be part of a well-constructed and continuous programmeof information and education, with well defined scientific elements and essential data:it is not necessary to know "a lot" but ''the little" that is known should be correct. Itoften happens, in fact, that an extremely accurate knowledge is possessed on specificscientific topics whilst very little is known of the mechanisms and interactions thatregulate Earth dynamics.It is therefore clear that an Environmental Education programme of this typeshould find an appropriate ground: in our opinion school education is the right areain which a stable and lasting intervention should be practiced. For the great majority,this kind of knowledge is received only or essentially in the period of compulsoryeducation and in any case notions acquired at school are nearly always the startingpoint for wider and deeper studies. Also conferences, debates, television broadcastingand newspaper articles in general can accomplish the task of popularisation andspreading information very well, but only if they manage to avoid the temptation offollowing fashions or being sensational at all costs.Information should help in the perception, identification and, at least, in thepartial understanding of natural phenomena. One should have the awareness that inorder to face a natural phenomenon correctly it is necessary to approach itscientifically and not emotionally, that is, present it as a problem remembering thathypotheses must be formulated by means of direct observation and data acquisition.Indeed, only after the collection and analysis of data is it possible to verify thehypotheses and therefore draw some conclusions. Especially today, in a globalhistorical, political, economic and cultural context, disciplinary problems have noreason to exist and should be solved with any possible means to obtain knowledge,in a close interaction between physical and biological variables. This complexityinevitably arouses some difficulties also caused by the spatial overlapping of elements

223having different temporal evolution.Moreover, as regards the environment, it is clear that, besides forecasting, it isnecessary to insist on the possibility of controlling the phenomena, or at least of somephenomena. In many cases in fact the forecast and understanding of events can beachieved, but they cannot yet be controlled.Environmental Education should have as a final goal a closer approach toNature, not only by means of immediate instruments such as the eyes, the touch, thefeelings and emotions, but also by means of the instruments of knowledge andconscience.6 GEOMORPHOLOGY AND ENVIRONMENTAL IMPACT ASSESSMENT6.1 IntroductionWhen a project is undertaken there are several effects on the environment in whichit is inserted. These effects can be of various types: quantitative and qualitative, director indirect, short or long-term, permanent or temporary, single or cumulative, positiveor negative, etc., and include also those that can occur during the construction anddecommissioning phases (see Wathern ed., 1988).Seldom have these environmental problems been a condition or a part of planning.Indeed, the aim of the impact procedures is to ascertain beforehand, by means ofanalytical approaches, whether the changes brought about in the environment permitthe re-estabilshing of an acceptable balance in the use of environmental resourcesboth for the defence of public health and people's living conditions. The feasibilityof a project can be assessed on the basis of the results of these studies, in relation tothe impact foreseen on the environment and the identification of risk levels. If theresult is negative, studies will have to show the modifications which will have to bemade to the enterprise so that it can be compatible with the environment, or possiblealternatives that could reduce its negative effects. The importance of a precautionaryevaluation of a project's consequences, has led to the definition of systematic andintegrated procedures based on various technical, administrative, scientific, social,etc., parameters.Environmental Impact Assessment (EIA) is a procedure for assessing the environmentalimplication of a decision to implement policies, plans, programmes andprojects. Thus, the scope of an EIA system could encompass all these undertakingsat all levels of government. Lee & Wood (1978) have suggested a tiered comprehensivesystem applied to a sequence of action categories and administrative levels (Fig.97). However, the vast majority of environmental impact statements in differentcountries have been related to projects.The first country that officially introduced the procedure of impact evaluation wasthe United States of America: in 1969 a law (NEPA = ''National Environmental

224Nationalfederal/c0)Ec^ORegionalstateCD>(DSubregionalLocal/Projects Programmes PlansCategory of actionPoliciesFig. 97. Categories of action and levels of government within a comprehensive EIA system (after Lee &Wood, 1978, modified).Policy Act") established the principles of environmental policy in that country. Itintroduced a series of norms for the preventive evaluation of impacts: the ''EnvironmentalImpact Statement" (Council of Environmental Quality, 1973). Afterwards,other countries, in particular France, the United Kingdom, Canada and Australia,adopted similar procedures.On 27 June 1985 also the European Community acknowledged this need andadopted a Directive making environmental assessments mandatory for certaincategories of projects. This Directive is applied to projects that owing to their nature,size and location can determine a considerable impact on the environment. Two kindsof project categories should be taken into account in this evaluation: those that in anycase produce serious effects on the environment and therefore necessarily imply anEnvironmental Impact Assessment (EIA); those that may have serious environmentalconsequences according to circumstances: for the latter category the compulsorinessof the EIA will have to be established for each individual case.As regards the impact studies, it is necessary to identify those environmentalcomponents which are not only particularly significant to the environment itself butalso sensitive to the work that is going to be carried out in a certain territory; theseare named environmental indicators. They are employed both in the description andinterpretation of the environment, in the planning of the location of a certain project

225and within the radius of influence of the project itself, as well as in the impactidentification and evaluation phase, concerning the influence produced on theindicators.For identifying and assessing impacts, surveying and monitoring systems are usedwhich refer to environmental indicators and transfer the data into adequate controllists or cause-effect matrices (see Leopold et al., 1971).A subsequent phase will consist in attributing a weight, that is an environmentalvalue to each indicator, in order to assess impact and identify a priority order ofimportance. This allows corrective operations to be carried out in order to reduce orcompensate the impact effects and assess the compatibility of the planned work withthe environmental characteristics of the territory.Here it is not the case to go deeply into the complex general themes of EIA,regarding which the reader is referred to the above mentioned authors and theirrelative references, but in the following chapters the problems concerning Geomorphologymore specifically will be dealt with. Also the conceptual and methodologicalbases used for some research of an European Union contract' (see Marchettiet al., 1995; and more in particular: Bollettinari, 1995; Panizza, 1995; Rivas et al.,1995; see also the final publication: Panizza et al., 1996) will be illustrated.6.2 ConceptsFirst of all, research must be carried out to identify the three main groups ofgeomorphological components, which may be treated differently (see Panizza, 1995):processes, landforms and raw materials (Fig. 98).>O-iOXa.ccOoUJoPROCESS —(e.g. cliff evolution)LANDFORM(e.g. sea beach)RAW MATERIAL —(e.g. littoral deposits)-^ ASSET(if valuable, e.g.for social value)-> ASSET(if valuable, e.g. foreconomic value)HAZARD(if hazardous, e.g.for landslides)RESOURCE(if used, e.g. assea-side resort)RESOURCE(if used, e.g. assand quarry)Fig. 98. Conceptual basis of the relationships between two of the geomorphological components(landforms and processes) and a project.'Human Capital and Mobility Contract ERBCHRXCT 930311 (Coordinator: M. Panizza).

226Figures 99 and 100 show in synthesis the conceptual bases of the simpHfiedrelationships between the above mentioned geomorphological components and theproject.In particular, the processes which when hazardous are geomorphological hazards,may interfere with a project, which is always characterised by specific vulnerabilityand cost (Fig. 99). The activity of these geomorphological processes may producedamage for the project, that is to say a risk for the project. This is the case of alandslide (geomorphological hazard) which may damage a motorway (project). In thissituation the natural component of the environment shows an active role and theproject a passive role.Furthermore, particular landforms which if valuable are geomorphological assets,characterised by specific fragility and value, may be affected by a project (Fig. 99).The effects on geomorphological assets deriving from the implementation of a projectmake up a direct impact, which causes environmental damage for the same assets.This happens, for example, when the construction of a road ruins a glacial cirque. Inthis case the natural component of the environment has a passive role with respectto the project which plays an active role itself.Nevertheless, it should always be remembered that there are some processes thatcan be considered as beneficial (e.g., a particular kind of erosion which may beconsidered as an educational example). However, these processes produce a landformand then can be included in it.The same considerations can be made for particular raw materials which ifvaluable constitute geomorphological assets: the interferences with a project mayproduce a risk or a direct impact (Fig. 100).landformsGEOMORPHOLOGY| processesenvironmentaldamagedamage to theprojecta = in active positionp = in passive positionFig. 99. Conceptual basis of the relationships between two of the geomorphological components (rawmaterials and processes) and a project.

227raw materialsGEOMORPHOLOGY ^ processesGeomorphological bhazards jdamage to theprojectFig. 100. Types of thematic maps for Geomorphology and EI A studies.a = in active positionp = in passive positionAlso in this case there are some materials that can be considered as hazards (e.g.,salty soils meta-stable sands). However, these materials are the result of particularprocesses and therefore can be included in the latter.6.3 MethodologyResearch should be carried out following the scheme below (Panizza, 1995).1) Types of Projects.2) Investigation phases.3) Mapping.4) Indicators.5) Evaluation of Hazards and Assets.6) Evaluation of Impacts l.s.7) GIS Methods.6.3.1 Types of ProjectsThe norms of the European Union for EIA's studies cover essentially the followingtypes of projects of the 1st category, here subdivided into groups with analogouscharacteristics for geomorphological research:a)b)c)— refineries;— chemical plants, plants for coal aeration, asbestos mining processes, etc.;— thermic and nuclear power plants;radioactive and toxic waste plants;transport infrastructures (motorways, railways) and airports;

228d) commercial harbours and navigation lines.Owing to the connections with Geomorphology, also the following projects from thesecond category can be taken into account:e) tourism infrastructures;f) land use change;g) mining activities.6.3.2 Investigation phasesThe investigation phases can be defined as follows, with progressive increases ofdetail and scale.I = Reconnaissance — general evaluation — site selection: general studies on asmall scale in a large area.II = Site and specific investigations: verification of the technical suitability of theselected sites.III = Detailed planning of engineering works: research and detailed measures.IV = Monitoring.V = Mitigation.There are moreover three steps normally followed for the development of a project:1) design;2) operation: — construction;— functioning; and3) decommissioning.EIA investigations should be carried out in Phases I and II so that the results can beincluded in the detailed planning and design of the project (Phase III). This planningphase should include proposals of monitoring during construction and recommendationsfor mitigation measurements to be included.As construction proceeds, more information will become available, particularlyabout the materials and the subsurface conditions.Also a failure of the design may occur.In carrying out diagnosis and remedial measures it may be necessary to modifythe predicted EIA. The procedures to be followed will, however, be the same.During the functioning operation it is recommended that the degree of success ofthe predictions and impacts is evaluated as a guide to maintenance routines and futuredesign practice. In the decommissioning operation it will be necessary to design anew EIA, in order to predict the effects of the abandonment or dismantling of theplant (e.g., pollution, uncontrolled mine drainage, etc.).6.3.3 MappingThe types of thematic maps used for these EIA studies are summarised in Fig. 101.They are both base maps and derived maps, to be used at different scales accordingto the investigation phases: for example a small or medium scale map for phase I, adetailed one for phases II or III.

2293.3.a = geomorphological map3.3.b= geotechnical map }• base3.3.C = hydrogeological map }3.3.x = hazard map (from: 3.3.a - 3.3.b - 3.3.c)3.3.y = landforms - assets map (from: 3.3.a)3.3.Z = raw materials - assets map (from: 3.3.a - 3.3. b) J}^ derivedFig. 101. Conceptual and methodological scheme of the role of Geomorphology (landforms and processes)for the EIA and a project.As for thematic base mapping, it is possible to make reference to various geomorphological,geotechnical and hydrogeological maps, well-known in literature. Asfor thematic derived mapping it is possible to make reference to some examples ofstability and hazard maps made by some groups of researchers; however, examplesof thematic maps concerning geomorphological assets are rarer. The derived thematicmaps can be integrated with data from literature, archives, databases, etc. Duringinvestigation phase I more general maps like morphometric and morphographic mapscan be used.For example, with respect to the hazard maps (concerning geomorphologicalprocesses) references may be made to the contents of chapter 3.9. On the other hand,as regards mapping of geomorphological assets, reference should be made to thecontents of chapter 2.3.6.3.4 IndicatorsIn the specific literature various definitions of the term indicator have been givensince this word may be applied to all the variety of environmental aspects, rangingfrom geological indicators to urban ones, to quote just two. Although varyingconsiderably from one author to another, involved in Environmental ImpactAssessment, all the definitions of this term show the need to emphasize in asignificant and summarised way an environmental phenomenon. In the specific case,a geomorphological indicator should describe a situation, a geomorphological processand, according to the situations, also its evolutive trend and its susceptibility to anexternal intervention. Therefore appropriate indicators should be selected for eachassessment investigation in order to acquire an exhaustive but concrete picture of thespecific situation; at the same time, all those not strictly necessary should be omitted,in order to avoid accumulating an excessive burden of data which would make thework unmanageable from an economic point of view.Impact is expressed by the changes affecting an environmental unit following theimplementation of a project. These changes will be emphasised just by the indicatorswhich depend both on the environment and on the project.Example. Let us consider an arenaceous slope subject to natural erosion producing

230sandy debris. The detritus accumulates in a riverbed at the bottom of a slope and issubsequently carried as far as the sea and deposited along the coast. It is obvious thenthat any human intervention on the slope will alter the pre-existing equilibrium. Infact, if the slope is totally or partially covered with concrete (project), erosion willeither stop or decrease and therefore the production of detritus will tend to zero. Asa consequence, the river will no longer receive the input of material that determinedits pristine balance and the energy previously dissipated in the load and transport ofthe sandy sediments will be mainly directed to fluvial erosion activities. Supposingthe riverbed is made up of clayey rocks, the material removed will no longercontribute to the replenishment of the pre-existing beaches, contrary to what happenedwhen the transported material was made up of sand. Consequently the beaches, thusdeprived of adequate solid supply, will retreat. This example is shown just to quotesome of the processes that take place when the slope conditions undergo changes.Also other processes could occur, such as interference with the groundwater orundercutting at the slope toe. In such a case the process indicators to be found are:one in the fluvial system and the other in the coastal one.In order to evaluate indicators for hazards and assets, it is important to considerthe scale and the density' of particular hazard processes and/or geomorphologicalassets. The lifetime of the project must be considered in order to evaluate thehazardous processes which can be at risk for the project or can be induced by theproject. It is therefore necessary to prepare a list of indicators for hazards and assets.From this point of view, the frequency of the processes must be evaluated andcompared with the lifetime of the project.According to the main groups of geomorphological components, the investigationphases and the scale of investigation, the indicators will be subdivided into threegroups:A. Morphometric and morphographic.B. Hazards.C. Resources.6.3.5 Evaluation of Hazards and AssetsThe evaluation of hazards should be developed using different methods:1) Direct measures (e.g., on scarp retreat).2) Mechanical models and calculations (e.g., geotechnical measurements).3) Crossing of ''causes" (e.g., overlapping thematic maps).4) Statistical approach of ''effects'' (e.g., recurrence of landslides).The first method consists of direct measures of some indicators. In the case of anactive cliff the measure of the risk for a project on the top of the cliff itself, may berepresented by the direct measure of the retreat of the slope or the variation in theslope angle, etc.The second method is developed using geotechnical measures and engineeringmodels. For example in the cliff case geotechnical parameters and engineering modelsmay be used in order to evaluate the retrogradation of the cliff.

231The third method takes advantage from the crossing of different thematic mapsin which the indicators are considered. For example, in the case of the abovementioned chff the evaluation should be estimate by the overlapping of differentmaps such as lithological, morphometric, vegetational, etc.The fourth method requires a good knowledge of many parameters in a large area.On the basis of statistical behaviour a forecasting of hazardous events can beevaluated. For example, in the cliff case, the retreat of the slope can be predicted onthe basis of the general retreat along all the coast.The evaluation of assets is described in 2.3.The hazards and assets will be related to the following groups of morphogeneticunits:1) Weathering.2) Slope:a) soil erosion/sedimentation; andb) mass movements.3) Periglacial (including special mass movements).4) Glacial.5) Fluvial.6) Coastal.7) Aeolian.8) Karst.9) Subsidence.10) Groundwater.6.3.6 Evaluation of ImpactsStarting from Figs. 98 and 99 it is possible to indicate a conceptual and methodologicalscheme of the role of Geomorphology for the EIA of a project, with thespecification on how the active and passive elements combine in giving differenttypes of impact is. (broadly speaking) (Cavallin et al., 1994).Figure 102 takes into account the geomorphological components landforms andprocesses. Beside the consequences in terms of risk and direct impact shown insection 6.2, a project during its implementation, functioning and decommissioning,may produce induced hazards, i.e., hazards which did not exist in the area before theintroduction of the project. These induced hazards may give rise to three kinds ofinduced direct and/or indirect effects: direct risk, indirect risk and indirect impact(Fig. 102).Direct risk can be delineated as the effect on the project of a hazard induced bythe project to itself; in this case a reflexive action takes place. For example, theconstruction of a road may cause the instability of the slope where this road is built,thus endangering the project.Indirect risk consists in a hazard induced by a project which damages thesurrounding settlements. This is the case of a landslide induced by a road cut, whichendangers a village located in the vicinity of the project.

232environmentaldamageINDIRECT RISKK""T^RISKTon the surrounding damage to thesettlementsprojecta = in active positionp = in passive positionr = in reflexive positionFig. 102. Conceptual and methodological scheme of the role of Geomorphology (landforms and processes)for the EIA and a project.Finally, indirect impact refers to the effects of hazards induced by a project ongeomorphological assets existing in areas surrounding the same project. For example,the filling of a lake, which is considered a geomorphological asset, due to a landslidetriggered by the construction of a road.The same considerations can be made by taking into account the geomorphologicalcomponents processes and raw materials.For the evaluation of the different types of impact l.s. mentioned above, for eachtype of project (6.3.1) and for each investigation phase (6.3.2), the main researchinstruments are the maps (6.3.3) and the indicators (6.3.4).6.3.7 GIS techniquesGeomorphologists have long recognised the importance of morphometric studies. Theavailability of altitude data in digital format, and the possibility of preparing andanalysing Digital Terrain Models (DTM) may be important tools for quantitativelyanalysing topographic elements (see Pike, 1993). Software packages specificallydesigned to produce high fidelity DTM are now available (e.g., Carla et al., 1987;Carrara, 1988) and to produce derivative maps such as slope, aspect and so on.The principal aim is to design and apply a structured method for EIA studies inthe field of geomorphology, including data collection, updating, modelling and analysis,using GIS techniques to automate and optimise the decision-making processes.Part of the required parameters for an evaluation of the impact on assets consistsof subjective analytical expertise, weight setting, application of nonspatial indices,etc., that cannot be applied directly in a GIS. Nevertheless, some of the criteria needa spatial definition a priori, such as all phenomena occurring in the study area or in

233the area of influence where GIS apphcations can be partially or completely included.In most cases, though, it becomes evident that a GIS represents a convenient tool forinterpreting the data necessary for the assessment in terms of feasibility analysis,robustness of the impact measurements, sensitivity and comparability analysis withspatially referenced information. Much work is still required, however, to bringspatial data analysis, geomorphology and EIA into the realm of routine proceduresusing widely accepted and significant standards (Patrono, Fabbri & Veldkamp, 1996).6.4 Quantification of impact**in collaboration with Mauro MARCHETTI6.4.1 Raw materialsThe methodology proposed by Rivas et al. (1995) is presented below. It has beenused in the already cited Human Capital and Mobility Contract.The types of direct impact on geomorphological raw materials which can takeplace as a result of different activities are:— consumption as a consequence of direct extraction;— sterilisation as a result of activities which make the resource unusable;— permanent sterilisation;— temporal sterilisation; and— degradation due to pollution which can alter the properties of the material.In order to quantify the impact on existing raw materials in a given area, thefollowing parameters have to be considered:V: total volume of the deposit (m^);v: % total volume affected;u: % of useful material;P: price ($m'^). The price of a resource is usually directly related to its quality,rarity and exploitability.R: reversibility of action (dimensionless: 1 to (-1)). Obviously the degree ofreversibility depends on the type of project; we can consider the minimumreversibility (-1) for those projects which imply the irreversible covering(construction on top) of the deposit for an unlimited time (nuclear power station,urban areas, roads, dams, etc.); reversibility near to 0 is applied to activities suchas forestry, agricultural uses or holiday villages, where the technical measures fordecommissioning are more feasible (-0.01 times years of implantation of theactivity); -0.5 for legal limitations, such as National Parks, etc. When the projectdoes not limit the use of the resource, the value of reversibility is 1;a: relative abundance or rarity is the affected resource volume or area divided by thetotal resource volume or area (dimensionless); the geographical area used asreference could be the region, province, or the area within a certain distance ofthe project;A: accessibility is a measurement obtained by the division of the number of potential

234users (inhabitants) within a certain radius of the resource and the distance (D, inmetres or km) of the resource from the nearest road (H/D); the quotient A^JA^^^,will always be

235E - ecological support.In the last equation they are (usually) equal to 1, unless one of them is put inevidence (then >1) or, on the contrary, is disregarded (then

236The indices of impacts here presented consider the impacts as a loss in terms ofquaUty; in particular the closer to 1 are /, and Ij^ the greater is the damage to thelandforms themselves.Other relevant parameters to be taken into account are visibility and reversibility,which are, in the case of landscape, directly related to mitigation procedures.6.4.3 ProcessesA methodology proposed by Bollettinari (1995) and applied in the already quotedHuman Capital and Mobility Contract is here illustrated.This methodology is founded on the principles which were presented in paragraph3.9 and is used for the assessment and mapping of the geomorphological hazards.According to this methodology, each unstable area is catalogued and accompaniedby a detailed list of the processes in action and/or the causes favouring instability.Significant parameters for the quantitative evaluation of hazard, or the environmentalcomponents which cause instability, should be established for all the territoryaffected by the project.The factors favouring environmental degradation (F) are the lithological,hydrological and climatic conditions as well as the indicators related to possibleprocesses taking place in the study area (/).Whereas the former offer on the whole a picture of the actual or potential causesof instability, the latter show the effective processes in action at the moment ofinvestigation.Each parameter chosen is considered separately from the others and quantitativelyassessed through the attribution of a weight for each unstable area thus identifiedduring the first phase of the research.The weight is attributed by the operator on the basis of the knowledge acquiredduring field investigations, with reference to previously fixed standard values.The sum of the scores attributed to each parameter (F and /) gives for each areathe assessment of hazard (V^J.F^ ^ F, ^ ... ^ F - L ^ I, ^ ... - I = V1 2 /! 1 2 n px(for area x).On the other hand, the sum of the hazard's values obtained for each area givesan appraisal of the global hazard for the territory examined {V^TOT) before theaccomplishment of the project.V + V + ... + V = y rnrpx py pz pTOTThe same procedure for the attribution of weights to each parameter chosen must berepeated with reference to the hypothetical situation which would be determined after

237the completion of the project.The value thus obtained {VpTor) provides information on the hazard conditionsaffecting the territory investigated following the accomplishment of the works (orgives information on territory instability after the project has been carried out. Itshould always be kept in mind that a V'^TOT ^^^ue greater than V^joj shows aworsening of stability and therefore emphasizes the presence of impacts).The difference between the value {VfyTor) obtained from the evaluation of theglobal hazard after the implementation of the project and the one calculated in thereal situation (that is before the execution of the works) gives the quantitativemeasurement of the modifications induced in the geomorphological environment, thatis the induced hazard (see § 6.3):H = VpTOT- V^pTOTA further stage of the research implies that the impact value should be againrecalculated taking into account the hypothetical final situation existing after theaccomplishment of possible mitigation measures capable of eliminating or mitigatingthe recognised impacts. Hazard {V\TOT) ^i^l have to be recalculated in thesehypothetical final conditions using the above described method. Finally, from thedifference between the hazard after the accomplishment of mitigation measures andthe hazard assessed after the implementation of the project, the value of residualinduced hazard will be obtained:// = V" _ yr '^ pTOT pTOTThe data thus obtained are summarised in a specific thematic map which can beeasily consulted even in subsequent phases of the project.7 CONCLUSIONSAs a conclusion of this book, in the prospect of a cultural union with and in the hopeof an integration between environmental values and humanistic disciplines, I wouldlike to mention the interrelationships between geomorphology, or more in generalgeoscience, and cultural resources and, in particular, archeological, historical andarchitectural ones. I think that this topic is particularly important today since we areliving in a period where the desire to preserve and emphasize these examples ofcultural heritage is particularly felt as well as the awareness that, following naturalevents or human impacts, these cultural assets could be definitively lost.These relationships may be summarised briefly as follows (Panizza & Piacente,1990, 1991).

2381) Environmental risks: from hazards that are earth-related (erosion, earthquakes,volcanoes, subsidence, etc.), water-related (floods, sea-storms, changes of levelof the water table, water pollution, etc.), air-related (hurricanes, tornados, airpollution, etc.) and hazards related to living beings (biological infestation, humanimpacts, degraded areas, etc.).2) Causes and effects: on the one side, the environmental factors that have led to theconstruction and the type of the cultural resource in question; on the other,forecast of the consequences on the environment of the various types ofconversion possibilities, both structural and those regarding its usage.3) Environmental education: informative and educational programmes for anintegrated knowledge of the environment in which the cultural resource is situatedand promotion of environmental awareness and consciousness.As regards geological risks, i.e., earth-related risks, it is sufficient to cite thefollowing as examples in Italy. Orvieto, Agrigento, Volterra, etc. for slopedegradation. Numerous cities known for their artistic importance in Friuli and Irpiniathat were damaged by the recent earthquakes of 1976 and 1980. Naples and Cataniafor volcanic hazards. Venice and Ravenna for subsidence-related problems. Theexample of Florence alone is sufficient to recall a historic city that has recentlyexperienced serious damage to its artistic heritage as a consequence of river flood.Together with other artistically endowed cities, Venice can serve once again as anexample to indicate the environmental factors that have conditioned a certain type ofurban design and architecture. At the same time, Venice itself is at risk of beingstifled and destroyed by an extremely intense tourist pressure in its historic centre,and by irrational industrial development in the surrounding areas.A strong emphasis on an interdisciplinary approach is required for such complexresearch which intends to focus on the functional-historical lines of urban developmentand to interpret the comprehensive series of events of each archeological,historical and architectural monument that make them up. This emphasis will haveto be strong enough to stimulate the joint efforts of various specialised fields(geomorphology, archeology, petrology, anthropology, environmental sciences, naturalsciences, economics, the arts, social sciences, etc.). Only the coordinated efforts ofthese specialised fields will permit an understanding of the historic structures withinthe framework of their specific morphology and dynamics. Therefore it will bepossible to offer, to those persons responsible for making decisions, the means tochoose those agencies most capable of evaluating the functional end economicbenefits of each individual project. Assessments of the economic and social yield ofthe preservation and restoration projects, the criteria for reconstruction and conversionchoices, the indications regarding the type of use most suited for these culturalresources or parts of them, will also have to take into account the above-mentionedrelationships.The results of that must promote environmental consciousness, by means ofstudies that start from the analysis of the most remote causes, such as geologicalfactors, and eventually arrive at the most current causes, such as socioeconomicimplications. In fact, this cultural approach, which is based on the knowledge of the

239components that have determined and regulate to date the evolution of the variouscharacteristics of an area, represent the only proper instrument to create an awarenessof the environment and the indispensable premise to its correct use.

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263BiographyMario Panizza, professor of Applied Geomorphology and Head of the Earth ScienceDepartment at Modena University (Italy), doctor ''honoris causa'' in Geography atCluj University (Romania), president of the European Centre of GeomorphologicalHazards in Strasbourg (France), and member of the Executive Committee of theInternational Association of Geomorphologists. He has carried out scientific activityand professional work in numerous countries around the world.Professor Mario Panizza

265INDEXAbrasion 42, 88, 90, 112, 113Accelerated erosion 37, 205Active fault 185Active landform 193Active tectonic element 171Aeolian erosion 53Aerial photograph 78, 161, 169Aesthetic 28, 210, 221Agriculture 201, 203Alluvial plain 95, 99, 106Alluvial-fan 102Animal-farming 202Archeology 238Aspect 16Asset 9, 26, 31, 221,230, 232Assets map 229Atomic power 205Avalanche 136, 137, 141, 152, 156, 160,162, 208Avalanche hazard 156Avalanches 23Azonal 197Backshore 115Backwash 110Badland 59Bank erosion 91, 110Bathyal plain 120Bayhead beach 117Beach 115, 122, 209Biostasis 36Black-glacier 139Block-slide 181Bottom erosion 91, 93, 98Breaching 140Calanco 51Canyon 120, 129, 137Capable fault 167Cavitation 88, 90, 112, 113Channel erosion 63Channel pattern 98, 99Classification 2, 66Cliff 113, 121, 127, 128Climate 193Coastal degradation 112Coastal erosion 42, 112, 114, 122Coastal hazard 120Coastline 118Conservation 11Continental shelf 119, 125, 126, 129Continental slope 119, 128Corrasion 49Creep 54Culture 26, 210, 212, 221, 237, 238Cuspate foreland 118Dam 22Database 33, 76Debris fall 176Debris flow 71, 75, 101, 129, 136, 146, 162Debris slump 185Degradation 90Dendrochronology 75, 76Desertification 36Digital Terrain Model 84Digitalisation 34Dormant landform 193Drop impact 44, 55Dune 117, 135Dynamic conservation 221Earth flow 179Earth material 11Earthquake 139, 141, 148. 165, 173, 177,179-181. 183, 185, 222Ecological support 27Economic value 211Education 27. 213, 219EIA (Environmental Impact System)7, 28. 223, 225-228, 231, 233. 234Electric energy 19Endogenetic 1Environmem 4. 5, 10, 28, 135, 197, 201,205, 206, 209-211, 220, 223, 225,226, 236, 238Environment 6Environmental 7

266Environmental catastrophism 206Environmental education 214. 219. 238Environmental indicator 224Environments 14Equilibrium 210Erosion 37Erosion agent 198Erosion factor 38Erosion hazard 37Erosion pavement 54Erosional platform 114Exaration 49Exogenetic 1Fall 67Farming 204Fault scarp 167Flood 92, 93, 95, 100, 102, 106, 222Flood plain 95, 103, 108Floods 98Flow erosion 46Flow 68Forecast 217, 218, 222Forecasting 86, 223Foreshore 115Geographical Information System 32. 75. 87.232, {see also GIS)Geological erosion 37Geology 2Geomorphological 191Geomorphological assets map 229Geomorphological convergence 4Geomorphological dynamics map 193. 196Geomorphological hazard 6, 7, 35, 92, 190.193, 194, 216. 217. 226Geomorphological hazard map 194Geomorphological indicator 229Geomorphological map 21, 31. 80Geothermal energy 25GIS 232Glacial hazard 135Glacier 25Glacier's dynamic 143Glaciopressure 25, 150Global hazard 236Global Positioning System 84Groundwater pressure 85Gully erosion 51, 57, 59, 60Hazard 5. 230Hazard map 189. 191. 194. 229Hazard probability 215Hazard reduction 216Hazard resistance 217Headward erosion 101Historical archive 73. 183Historical records 164Human activity 5Hunting 201Hydrogeology 192Hydrographic network 99, 102IMPACT 6. 7, 13, 15, 28. 119, 125, 198,206. 209, 211. 223. 225. 228, 231,234, 237Impact 9Impedance 193Inactive landform 194Indicator 225. 229. 232Innovation 11Inshore 115Instability 35. 190. 191Integrated analysis map 191, 196Inundation 91. 106, 107Isoseismic-line map 183Jokulhlaup 147. 162Karst 179Lagoon 118. 124Lahar 149. 188Land use 63. 193Landslide 22. 135Landslide causes 68. 70Landslide dating 75Landslide hazard 64. 66. 81, 86, 87Landslide hazard assessment 65Landslide inventories 74Landslide investigation 72, 73Landslide susceptibility 87Lateral spreading 182Lava 187Lava flow 187Littoral barrier 118Longshore bar 117Longshore current 111Man 6. 26. 65. 119, 126, 197, 220Map 19, 80

267Map of geomorphological assets 31Map of slope aspect 18Mapping 79Marine hazard 110Meander 99, 100, 105Men 234Meteorological parameters 85Microclimatic changes 203Mitigation measurements 228Model 3, 55, 58, 60, 63, 88, 183, 209,218, 230Monitoring 81, 84, 218, 228Morpho-neotectonic 166, 169Morpho-neotectonic map 171Morphoselection 49Mountain climbing 149Mud flow 149Natural equilibrium 209Natural resource 207Natural system 210, 214, 220Nature 198, 222Neotectonic 167, 173, 183Neotectonic map 172Newmark method 185Newspaper 222Normal erosion 37Offshore 115Paleoseismology 185Pedogenesis 15, 16, 36Pedology 60Periglacial hazard 135Permafrost 160, 164Photogrammetry 79Piping 50Planning 216Plunging breaker 110,116Pollution 206, 212, 222Population 201, 213Prediction 86, 138, 217, 218Progradation 116Proluvial fans 91Pseudokarst 50Quatemar 3Quaternary 2, 127, 168Rain erosion 43Raubwirtschaft 197Raw material 7, 8, 13, 19, 28, 206, 225,232. 233Reflection 110Refraction 118Remote sensing 76, 168Reserve 8Reservoir 21Resource 5, 8, 14, 16, 19, 25, 27, 36, 126,197. 205, 206, 212, 218, 223, 230,234. 237Retrogradation 116Reynolds' number 38Rhexistasis 36Rill erosion 57, 59Rill flow 46RISK 6, 7, 9, 26, 65, 98, 121. 122, 130.135, 156, 164, 188, 205, 209, 211,214-216, 223, 226, 228, 230, 231, 238Risk mitigation 8, 217River degradation 88River erosion 88, 90, 94River hazard 88, 92River transport 98Rock avalanche 75, 180, 185Rock fall 176, 180, 181, 185Rock glacier 159Rock slide 180, 185Sarma's method 185Scenic 28Schorre 118Seismic activity 174Seismic amplification 175Seismic hazard 165, 187Seismic risk 165, 187Seismic shock 72, 174, 176, 177, 180Seismic susceptibility 165, 172Slide 67Slikke 118Slope angle 18, 19, 117, 174, 176-178, 181Social system 220Soil 14. 36, 43, 50, 53, 55, 60, 202, 205, 207Soil avalanche 180Soil erosion 36-63, 36, 38, 60, 63Soil slide 185Soil vegetation 38Solar energy 18Solar energy map 19Solar radiation 16

268Spit 118Splash 44,49Spread 68Stokes' equation 40Subsurface flow 49Suffosion 50Surface deformation 83Surface erosion 37Surface fault 185, 186Tectonic fracturing 182Television 222Terrace 13, 176Thematic maps 228Tides 111Tombolo 118Topography 192Topple 67Transport capacity 47, 48Tunnel erosion 50, 51Upland erosion 63Vegetation 202, 203, 208Vibrating table 177Vibration 175Volcanic eruption 222Volcanic hazard 187Volcanic risk 187, 188Von Karman's universal constant 39Vulnerability 5, 7, 64, 165, 214, 215, 226Vulnerability reduction 217Wandering 99Water 19Water bubbles 145Water erosion 40, 42, 55Water pocket 144Wave refraction 110, 111Weather 85Wind 53, 111, 118, 205Wind erosion 5321-13001-210