ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

The Arlanc plain area of 100 km 2 is in the upper catchment.
Research has shown the diversity of the geomorphological
evolution in the floodplain for 2000 years:
-stability of channel and floodplain in the downstream
part of the valley;
- important instability in the upstream section.
Moreover, by means of deep soundings in the stream deposits
along the river, it was possible to obtain 14C datings
which put forward geomorphological changes during the
first part of Holocene period.
In Limagne the Dore flows away the north. We were specially
interested in the right bank. The left bank topography
had been recently modified by man.
In the right bank the alluvial plain is narrow (from 250 to
500 m). Farther to the east lies quaternary alluvial terraces
and sedimentary piedmont at the foot of crystalline mountain.
This part of valley is characterized by a lot of colluvial
fans located at the boundary between alluvial terraces and
the actual floodplain.
Indeed, the drainage network had largely dissected terraces
and sedimentary piedmont, creating steep slopes.
Many of these slopes had been deeply incised with valleybottom
gullies. Downstream of gullies colluvial fans spread
on the alluvial plains of the Dore and its tributaries. Moreover
some fans had been gullied. Therefore we have
identified two generations of colluvial deposits.
The combination of geomorphological analysis, historical
research and 14C datings gave some precisions about the
setting of these landforms. On the one hand, superior fans
were created from at least 8000 14C years BP. Usually,
deposits show fine-grained and silt load which indicates a
relationship between these accumulations and land use
changes.
On the other hand, inferior fans recover the old channel of
the Dore which is drawn on the historical plans and cadastre.
Fans were probably constructed during the 17 th and
18 th c., a period of intensive farming activities.
FRANCO CUCCHI 1, FURIO FINOCCHIARO 1 & PAOLO FORTI 2
Gypsum degradation in the Mediterranean area
with respect to climatic, textural and erosional conditions
1 Dipartimento di Scienze Geologiche, Ambientali e Marine,
Universita di Trieste, via E.Weiss, 2, 34127 Trieste, Italy
2 Dipartimento di Scienze della Terra e Geologico-ambientali,
via Zamboni 67,40127, Bologna, Italy
Many are the experimental studies performed on the meteoric
degradation of carbonate outcrops (Cucchi & alii,
1996; Trudgill 1977), but until now no one on the same
phenomenon on gypsum.
The lowering of the gypsum surfaces was measured using
the micro-erosion-meter (TrudgyIl1977): this method was
proved to be far more suitable than the tablets one (Calaforra
& alii, 1993), the systematic errors being limited to
less than 0.05 mm.
In the last 8 years over 4000 data have been collected in 35
sites of Italy and Spain, selected for their different climatic
and morphologic conditions in the range between the 47
and the 36 parallel. The study was related to over 20 gypsum
lithotypes different in petrography, texture and crono
stratigraphy.
Rainfalls ranged from 1500 to less than 150 mm/yr. and
the observed lowering from 3 to 0.05 mm/yr. The wide degradation
range reflects the dramatically different environmental
conditions in each of the experimental spot.
Anyway it was possible to detect the fundamental role of
the water flow regimen in gypsum degradation, which is significant
only with turbulent flow.
The mean degradation value for the whole area resulted of
0.78 mm/1000 mm of rain, which means an average 0.65­
0.70 mm/yr. in the Mediterranean region. This relatively high
value is the first experimental proof that the karst cycle
in gypsum is always extremely young, no outcrop of this
rock surviving more than a few hundred thousands years.
ELZBIETA CZYZOWSKA
Flood events recorded in the alluvial fan sequences
Department of the Geomorphology and Hydrology of Mountains
and Uplands, Institute of Geography and Special Organization,
Polish Academy of Sciences, sw. Jana 31-018 Cracow, Poland
The detailed reconstruction of transportation and deposition
in the very unstable environment of the alluvial fan is
very difficult.
On the base of the detailed sedimentological analyses of
the present and fossil fan sediments, we can separate several
sequences of layers recording the single flood events.
The sequences built from several layers (from three to five,
six) showing pensimetric grain size is rarest. The middle,
coarsest layer is record of the highest discharge. Underlying
layers record the rising water level (coarsening of
sediment). Overlaying layers showing finer sediments
towards the top are the record of the falling water level.
The sequences built from two or three (sometimes - four)
layers showing finer sediment towards the top are more
frequent. These layers reflect only late phase of the flood
event. The sediment sequences of the rising water lever
phase is missing, these is the erosion phase.
Third and most frequent sequences formed during single
flood events is built from one or two layers which does not
show grading changes. This record represents only end of
falling water lever or highest discharge. Discontinuity of
the record of the falling water level may be due to increase
of erosion or shift of the water course.
The flood deposition in the alluvial fan surface takes a space
variability course which is conditioned by varying fan alluvial
relief and alternate occurrence of the erosion and deposition
phases during the same flood event. The course of
the flood wave should be also taken into consideration.
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