ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

magurskie layers, hieroglyphic and others are medium resistant
or soft. The roof of the overthrust is folded into numerous
anticlines and synclines and in some places there
were developed small overthrusts. Anticlines are mainly
very narrow with thrust slices and their axis zones are built
of soft rocks. Synclines, in hard magurskie sandstones are
wide and flat. Besides there are numerous horizontal
faults. Deposits of magurska overthrust have been flattened
by the Beskidian planation surface, age of which was
estimated for the sarmatian. In the result of epicyclic uplifting,
lower planation surfaces have been formed and relief
inversion has taken place. Inversion has been the most
clearly marked in places where wide vales have been formed.
Wide, isolated hills have also been formed and plateaus
of them are on axes of crossing synclines. Wide, flat
plateaus turn into steep slopes with 30-50° inclination and
into gentle foothills of glacis-pediment character. Isolated
hills are separated by inversional valleys or dales formed
on anticline axes. Analyzing the valley pattern it can be stated
that big valleys were formed in soft deposits and they
are accordant to the run of layers. They are subsequentinversional
valleys, longitudinal profiles of which are
smooth. The valley pattern is rectangular and is accordant
to longitudinal and transversal elevations or horizontal
faults.
Evolution and transformation stages of relief in the Beskid
Wyspowy was greatly influenced by varied lithology, resistance
of deposits and rectangular pattern of anticlines and
synclines within the magurska overthrust.
Hill slopes are modelled by numerous, deep, rocky landslides
which mark present development and pattern of valleys
which cut the slopes. Researches on origin and pattern
of landslides pointed out that in spring areas of the Beskidian
streams there is a step-like pattern of deep, post-landslide
embarked niches or crevices filled in with debris.
Landslide pattern is often radial or bifureated and their niches'
formed within resistant sandstones, are very clear.
There are subsequent landslides within loosening zones
and within schists. Landslides within the Beskid Wyspowy
have been many times rejuvenated and presently they move
back up the slopes. In the result bodies of younger landslides
are stopped in bottoms of old landslide niches and
form step-like profile of landslide slopes. Bodies of fresh
landslides built of clay-debris material are easily dissected
during heavy rainfalls. Mud- and debris-flows take place in
depressions then. In the result of those processes valleys
are formed. Majority of valleys radially cutting the slopes
of the Beskid Wyspowy were formed on traces of old, big
landslides.
Valleys which are cut in slopes create different patterns
which cannot be explained only by an activity ·of flowing
down waters. Distribution of longitudinal and transversal
cracks, location of rocky packs and stages of development
of landslides going backwards up the slopes or rejuvenated
in their lower parts make conditions for v-shapped valleys.
They are formed in depressions, often without outlet
within the landslide areas.
- Wide, valley landslides in the upper part form single,
forked valley pattern which in the first stage of develop-
ment is irregular. It often consists of depressions without
outlets in which periodically or continuously flowing water
disappears (northern slope of Salasz, Jaworz),
- Landslides rejuvenated in their lower parts make semicircular
(western slopes of Wielka G6ra) or zigzag (eastern
slopes of Lopien) valley pattern.
- Narrow, valley landslides influence formation of concentric
pattern of v-shapped valleys (southern slope of Salasz
and northern slopes of Lopien). It can be disturbed during
landslide rejuvenation.
- Wide, frontal slope landslides made forked-parallel
valley pattern (north-eastern slopes of Lubogoszcz and
Snieznica).
- Subsequent landslides on flaked flysch deposits make
post-landslide basins with steep slopes and often with
swampy, flat bottoms. Above the landslide niches there are
low passes in soft rocks.
JEAN-LOUIS BALLAIS
Evolution of a gully in Lower Provence (France):
preliminary results (October 1991-February 1996)
Institut de Geographie et Cagep-Ura 903 Cnrs, Universite de Provence,
29 avenue Robert Schuman, 13621 Aix-en-Provence Cedex, France
The Aurigon gully is about one hundred meters long ant
its watershed is about one hectare. It is cut into Upper
Cretaceous claystones on the Sainte-Victoire mountain
southwestern piedmont.
In view of putting in an erosion measurement station, a
preliminary equipment has been made using 42 pegs. The
goals of this equipment were to locally measure accumulation
and erosion and to know the present day processes.
The main methodological problem has been the instability
of pegs: we were obliged to use 275 of them. This instability
is due to natural causes (pegs washed away mainly in
the main talweg or in the rills) and to human causes (pegs
pulled out by strollers). 54 series of measurements have
been performed but the longest continuous series is only
51 measurements. The uncertainty about the true location
of the lost peg and the disruption of the claystones due to
driving in of the new peg reduce the validity of the results.
On the whole, 2734 measurements have been performed
that is to say 63,5 per peg.
Fields observations show that claystones are superficially
altered by several processes: hydroclasty and pellicular solifluction
everywhere and gelifraction and pipkrakces gelifluction
in winter on the ubacs. This centimetric layer produces
small dry screes that can be assisted by wind or by
strollers passages. This thin layer is also removed by hydraulic
processes during rains: very efficient splash and rill
erosion. Rills are cut into the non altered claystones, excepted
on the ubacs. The most important part of erosion
occurs during intense pluviometric phenomenons (september
1993).
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