ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

Our project attempts to model the topographic evolution
backward as well as forward in time. First results indicate
that the initial topography rose abruptly at the time (and
location) of Alpine metamorphism in the mid Tertiary.
Subsequent tectonic uplift appears to be largely balanced
by denudation resulting in limited change of the topography.
Slow eastward spreading of the topography accompanies
the eastwards lateral extrusion since the mid
Tertiary.
TOSHIHIKO SUGAI
River valley development by concurrent fluvial
processes and climatic changes
Department of Environmental Geology, Geological Survey of Japan,
Tsukuba, Ibaraki, Japan
River terraces are important landforms to understand the
interplay of climatic changes with fluvial processes of incision
and sediment deposition. The Usui River is a tributary
of the Tone River that is the largest river in Japan. The
Usui River has a drainage basin area of 287 km 2 with the
maximum altitude of 1603 m a.s.l. Along the Usui River,
three well-developed terrace levels are observed. Each terrace
is subdivided into two segments: a filltop terrace
along the upper reach and a strath terrace along the lower
one. Three valley fillings with coarse gravel beds in the upper
reach correspond to the last three glacial ages of oxygen-isotope
stage 2, 6 and 8 based on the ages of marker
tephras. The positions of these valley fills migrated
upstream from the older terrace to the younger one.
To clarify the response of fluvial systems to climatic change,
terrace sediments were interpreted from the viewpoint
of paleohydraulics. Using the grain diameter of terrace sediments,
paleo-tractive forces were evaluated based on the
correlation between tractive force and grain diameter of
the sediment on the present river bed. The valley filling
was caused by the diminution in tractive force related to
the decrease in heavy rain produced by typhoons during
the glacial ages. During the interglacial ages, the reverse responses
occurred due to the increased incidence of
typhoons. The curvatures of the longitudinal profile of the
river channels of the glacial ages were decreased by the aggradational
processes, resulting in migration of the front of
the valley filling area. In contrast, the curvatures during the
interglacial ages increased by the degradational processes.
From another aspect of the development of river
landforms, the positions of the valley fills during the glacial
ages migrated upstream. Due to the increase in curvature
of the longitudinal profile of the preceding interglacial
ages, the positions of the segment where the tractive force
can transport coarse gravels migrated upstream during the
following glacial ages.
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VIRGIL SURDEANU
Grands glissements de terrain dans l'espace montagneux
de la Roumanie
Faculte de Geographic, Universite «Babes-Bolyai», 5-7 rue Clinicilor,
3400 Cluj-Napoca, Roumanie
Le travail present a comme point de depart l' acception
qu'un glissement de terrain entraenant plus de 1 x 10 6 m'
de materiel peut s'inscrire parmi les grands processus de
mouvement en masse. Par consequent, on s'adonne (l'analyse
de tels phenomenes produits dans l' aire des mouvements
orogeniques de la Roumanie, en particulier, dans les
montagnes cristallines et dans celles du flysch.
L' etude entreprise vise en premier lieu, les causes qui les
ont declenches : facteurs climatiques, tremblements de terre,
interventions antropiques sur l'environnement. Selon
nous, 1'intrusion des activites humaines dans 1'espace montagneux
constitue la cause principale des grands desastres,
Dans Ie cas des glissements contemporains on en analyse la
dynamique en rapport etroit avec l'evolution des elements
cause. Les aspects morphologiques et morphometriques eu
sont soumis e 1'investigation en correlation avec le substratum,
le relief et aussi avec les surfaces affectees, pendant
des cycles anterieurs, par des processus identiques. La reinstauration
de l'equilibre s'est produite apres 10-15 ans.
Ayant a la base l'evaluation des degats anregistres a1'occasions,
nous proposons une prognose possible du processus,
tout en mettant en evidence les risques qu'il presuppose ou
entraine, Les analyses statistiques realisees concernant surtout
les montagnes du flysch nous autorisent aavancer cette
idee qu'ala fin du millenaire, il est bien possible qu'on enregistre
une recrudescence majeure de ces processus.
NICOLA SURIAN
Channel changes of a regulated river: the case of
the Piave River (Eastern Alps)
Dipartimento di Geologia, Paleontologia e Geofisica,
Universita di Padova, via Rudena 3,35123 Padova, Italy
In the last century the Piave River (Eastern Alps) has been
strongly regulated for production of electric power and for
irrigation purposes. The presence in the drainage basin
and along the main stem of many hydroelectric reservoirs
and diversions has significantly changed the river flows
and the sediment transport. Remarkable channel changes
are the river response to this regulation. The aim of this research
is to describe these channel changes trying to understand
the causes and the mechanisms of the changes. A
better understanding of the river dynamics in the past is
important both to improve regulation strategies and for
the management of the river in relation to floods.