ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

dence, however, that local Torngat ice tongues had retreated
up valley to the glacial cirque zone prior to disintegration
of the Laurentide ice sheet filling Ungava Bay.
Extreme contrasts in sediment cover, and in weathering of
bedrock at different altitudes in the Torngat Mountains
were observed, as they have been by several researchers
since the beginning of the century. Well preserved knifeedged
cirques are also characteristic features of the high
mountain zones, whereas subdued, worn down cirques
characterise the lower plateaux edges. The hypothesis developed
here is that these contrasts can be related to transitions
from cold-based to warm-based thermal regimes at
the base of local, thin and vigorously outflowing ice
streams. In order to support this interpretation, and to
provide chronological evidence for the latest, and possibly
for previous glacial events, cosmogenic dating results of
lOBe in bedrock and erratic rock samples are presented.
FLORINA GRECU & IONEL BENEA
The risk availability of the hilly regions:
mapping stages
Department of Geomorphology, University of Bucharest,
1 Bd. N. Balcescu, 72952 Bucharest, Romania
The Risk Map represents the final stage of a laborious analytical
approach. For the hilly regions, this map expresses
the vulnerability the lands have for degradation processes.
The most important variables that influence the risk availability
of the hilly lands, under temperate climate, are: lithology,
landforms (geomorphic processes, slopes, drainage
density), soil and vegetation. The stages of the risk availability
mapping are: geomorphic processes careful mapping,
confronting this map with the geological, soil and soil erosion
maps and with slopes, drainage density, fragmentation
depth and vegetation maps as well.
Then we took into account the geomorphic state indices
for the vertical erosion, areal erosion and the landslides.
These have been identified on the basis of a 1 square km
grid (scale 1:25000), considering the surfaces or the
lengths affected by the processes (SJ and the total area
(S}, and we used the formula Ix=(Sx/Sr)x100. The vulnerability
has been graded, according to the risk factors, into five
classes: 0.20; 0.21-0.40; 0.41-0.60; 0.61-0.80; 0.81-1.00.
We have selected for our study the Calva River Basin because
of the somehow uniform lithology (i.e, Pontian deposits
of sands with marl layers in-between) and a monodine
structure that materialises into a cuestas- type relief. The
size of the basin is 5 in the Horton-Strahler classification
system. The confluence ratio is 4.32 and the achievement
index is 1.34, these denoting a close-to-equilibrium stage
that the system has reached. There is still a high potential
for regressive erosion and valley deepening denoted by the
great number of first order size segments within the basin.
The interaction of the system's variables vary from horizontal
or merely horizontal surfaces to those of the slopes
riverbeds and floodplains as well. The result is a different
risk availability of each of these.
A. Flat interfluves and terraces (less than 5° inclination
angle) are generally not exposed to risk. The narrow interfluves
are incised by first order size torrents with regressive
erosion. Such interfluves are noticed along the Steana and
Valea Satului streams, under forests.
B. Hillslopes are the predominant landforms in the Calva
river-basin.
Slopes having low risk availability extend on both sides of
Calva, Valea Satului and Steaua rivers. They are represented
by slightly inclined glacises - less than 5° - which are
exposed to floods and coluvio-proluvial sedimentation
from upslope.
Flat interfluves, terraces and glacises are not degraded
lands and are used for agriculture.
Slopes having medium risk availability have different inclinations
(from medium to high) and are covered by forests
and brown luvic and albic luvic soils. This kind of slopes
extend on the left side of Calva river in its upper course.
Slopes having medium to high risk availability are deforested
slopes, very inclined, with deeply eroded soils. Geomorphic
processes as sheetwash and superficial landslides
affect them. Their agricultural potential is low and therefore
they are used for pastures or hay-making. There are also
old teracettes, all abandoned nowadays, that have favoured
land degradation.
Slopes having very high risk availability are the most inclined
ones, totally deforested, and the soils have been deeply
eroded. Sheetwash is overpassed by gully erosion and agriculture
is no longer possible on these slopes.
Slopes excessively eroded are also very abrupt, the free face
showing the bare rock. Soils have been completely eroded
away and torrents incised deep to 15-30 meters. Accacio
trees have been planted on small surfaces, but not very
successfully.
C. Floodplains present a medium risk availability mainly
because of flooding processes, while talwegs have been cut
into the floodplain deposits, being bordered by steep banks.
ROGER G. GRIBOULARD 1 , CLAUDE BOBIER 1,
PASCALE HUYGHE 2,
JEAN CLAUDE FAUGERES 1 & ELIANE GONTHIER 1
Morphologie sous-marine et tectonique active.
La partie meridionale du prisme d'accretion
des Petites Antilles
1 Departernent de Geologie et Oceanographic,
Ura/Cnrs 197,Universite de Bordeaux I,
Avenue des Facultes, 33405 Talence Cedex, France
2 Lgca, Universite de Grenoble, 15 Rue M.Gignoux,
38031 Grenoble Cedex, France
Le prisme d' accretion tectonique des Petites Antilles constitue
l'un des modeles les plus spectaculaires de zone de
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