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In Ireland the Quaternary or unconsolidated sediments over rock are mainly glacial tills, sands and gravels.Another important characteristic of the Irish landscape is that there are extensive tracts of peat bog, bothraised bog in the midlands, and blanket bog in the uplands and along the western seaboard. Both of these haveimportant ramifications for landslide susceptibility in Ireland.2.4 Factors causing LandslidingSlope failure can be due to a large number of factors. The engineering investigation of actual slope failure or thedesignation of areas of potential landslide hazard is highly complex. Landslides are a major area of research ona global scale with international conferences taking place on a regular basis at different venues around theworld. This research has become more and more interdisciplinary in nature. As a starting point, in order to setup a simpler framework for further analysis, the myriad of factors can be classified into two main categories.These are the background or conditioning factors and secondly the external or triggering factors.Conditioning FactorsOf fundamental importance are the physical characteristics of the slope which might make it prone to failure iftriggered by other external factors. These physical factors are many and varied and need to be documented inany slope assessment. The major ones are listed below.• Bedrock Geology – lithology, structure, texture, mineralogy, degree of weathering• Quaternary Geology – lithology, thickness, extent of discontinuities, degree of weathering• Geotechnical properties of bedrock and Quaternary sediments• Geomorphology – slope elevation, slope gradient, slope aspect, downslope profile, cross-slope profile• Hydrology – slope drainage pattern• Hydrogeology – water table level, permeability• Land Cover – vegetation type, land useTriggering FactorsThese are the external factors which can act on the slope to initiate landslides given the character of the slopeas defined by the various parameters listed above.• Earthquakes – not a major factor in Ireland• Volcanoes – active volcanoes not present in Ireland• Rainfall – total amount, intensity, time interval• Natural erosion – slope surface, base of slope• Man-made – undercutting of slopes, removal of retaining walls, land drainageMany of these factors are considered further in the later chapters which follow on the geotechnical aspects oflandslides and susceptibility mapping.8
3. THE IRISH LANDSLIDES DATABASERonnie Creighton3.1 The Need for an Irish Landslides DatabaseFundamental to the study of landslide hazard in Ireland is information on the extent of the problem in the past.This involves a listing of past events with data, where available, on location, landslide type, materials, causes,and impacts. This data can then be used to assess landslide hazard in the future by defining areas or zoneswhich might be susceptible to landsliding. From this baseline information risk assessment may be undertakenand a strategy for mitigation put in place.To date there has been no compiled dataset on slope instability in Ireland. This in part reflects the limited scaleof the problem in the past which in turn impacts on resources availability to undertake such research. The aimof the database being developed in GSI is to assemble as much information as possible from whatever sourceto produce a national map of landslide events with key attribute data, where possible, for each.3.2 Database StructureThe database is built in Microsoft Access. There are a total of nine related Tables, based on a one-to-onerelationship throughout, the key primary field being “Landslide_ID”. The tables are:-1. Landslide_Event2. Landslide_Weather3. Landslide_Terrain4. Landslide_Dimensions5. Landslide_Reference6. Landslide_Mechanism7. Landslide_Location8. Landslide_Impacts9. Landslide_Land_UseEach table contains a number of fields which are mostly text boxes while some are linked to Look-Up Lists.The database structure is set out in Appendix 4. Each table is linked to a Form for data entry and there are alsofull Query and Report facilities within the Access database. It should be said that as most of the entries in thedatabase to date are historic events there is no data to populate many of the fields in the various tables.However this design has been adopted because of the expectation that future slope failures will be documentedin a more detailed way so that the database can be used to the full. The exercise of populating the fields withthe data available for past events is an ongoing process.3.3 Data SourcesIn the absence of any national compilation of landslide events, an extensive trawl of as many sources aspossible has to be done to maximize the number of events recorded. Associated with this is a bibliography oflandslide and related references for Ireland. This is included in Appendix 6. In the database a reference sourceis listed for each event, so that the original source can easily be retrieved.The list of data source types includes the following:-Field Guides – published and unpublished guides by geological and other associations.Internet Search9
Page 1 and 2: Landslides in IrelandGeological Sur
Page 3 and 4: LANDSLIDESinIRELANDEditorRonnie Cre
Page 5 and 6: CONTENTSPreface ...................
Page 7 and 8: Fig. 4.3 Forces caused by water in
Page 9 and 10: PREFACEUntil recently Ireland has b
Page 11 and 12: een very important in populating th
Page 13 and 14: involves a report on the current st
Page 15 and 16: Main Objectives• Increase public/
Page 17 and 18: 1. INTRODUCTIONRonnie Creighton1.1
Page 19: 1.3 The Landslides PublicationThis
Page 22 and 23: Peat flows are not nearly so well d
Page 26 and 27: Journal - published papersLetter -
Page 28 and 29: Fig. 3.1 Two images showing the use
Page 30 and 31: Table 3.1 Landslide Events Per Coun
Page 32 and 33: Fig. 3.3 Location map of the Pollat
Page 34 and 35: 3.7.4 Quaternary GeologyQuaternary
Page 36 and 37: 3.8 The Derrybrien Landslide - 2003
Page 38 and 39: • The classification scheme shoul
Page 40 and 41: The force causing the block to slid
Page 42 and 43: Plate 4.1 Herringbone drainage syst
Page 44 and 45: 1210Number of events864Raised bogBl
Page 46 and 47: It is well known by research at Uni
Page 48 and 49: 5. LANDSLIDE SUSCEPTIBILITY MAPPING
Page 50 and 51: Two simplified hypothetical example
Page 52 and 53: 5.1.4 Mapping and GISBy definition,
Page 54 and 55: Platform / sensor pixel resolution(
Page 56 and 57: For this initial run, the criteria
Page 58 and 59: 42Fig. 5.5 Peat and peaty podzols f
Page 60 and 61: for susceptibility mapping purposes
Page 62 and 63: elationships between developed susc
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Page 66 and 67: 50Fig. 5.12. Landslide susceptibili
Page 68 and 69: 52Table 5.6. Landslide classificati
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As the dataset was not available at
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CHAPTER 5.2 - TABLE APPENDIXBedrock
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6. LANDSLIDES AND PLANNINGAileen Do
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6.2.4 Development ManagementThe phy
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6.5 Current Practice on Landslides
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7. LANDSLIDES IN NORTHERN IRELANDTe
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2. MudflowsPlate 7.1 Rotational Lan
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7.2 Carboniferous Cliff Lines (Co F
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8. RESEARCH ON IRISH LANDSLIDESKoen
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8.4 Research. Post-2003 AbstractsTa
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Identifying, recognizing, and predi
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In the case of vulnerability mappin
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Steep slopes in glacial tillMichael
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9. RECOMMENDATIONS FOR FUTURE WORK9
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Priority 1 Peat slides and peat str
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TEXT REFERENCESAcreman, M., 1991. T
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Skipper, J., Follett, B., Menkiti,
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APPENDIX 2Glossary of TermsBlanket
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APPENDIX 3Nomenclature for Landslid
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APPENDIX 4101
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Hammond, R. 1979. The Peatlands of
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APPENDIX 7Useful Web Linkswww.gsi.i
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