ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

une graduelle augmentation jusqu'a ce qu'on a 1'effet de
protection thermique neigeux. Au moment que la neige disparait
tout a fait, les variations de TS s' adaptent rapidement
a celles de TA mais avec retard (3 jours environ ala
profondeur de - 50 em et 15 jours pour profondeur de ­
150 em). Au dessous de cette profondeur les variations
sont tres faibles et les isothermes montrent une disposition
reguliere. Enfin, on a releves des ecartements qui semblent
etre lies ala variabilite granulometrique superficiel du glacier
rocheux, laquelle peut limiter ou faciliter la vitesse des
variations thermiques de l' externe al'interne.
MAURO GUGLIELMIN 1, CLAUDIO SMIRAGLIA2
& NICOLETTA CANNONE 3
The rock glaciers of the Lombardy Alps (Italy)
as indicators of mountain permafrost
1 Servizio Geologico Regione Lombardia,
via F. Filzi 22, 20124 Milano, Italy
2 Dipartimento di Scienze della Terra, Universita di Milano,
via Mangiagalli 34,20133 Milano, Italy
3 Istituto di Botanica, Universita di Pavia,
via S. Epifanio 14,27100 Pavia, Italy
The paper presents the results of the first rock glaciers inventory
of the Lombardy Alps (Italy). In this region by
means of aerial photographs 498 rock glaciers were individuated;
these landforms have been classified according to
their apparent degree of morphological activity in: active
(92) inactive (285), doubt (94); 27 landforms have been defined
complex. The following morphological and morphometric
parameters have been determined: the lowest altitude
of the front; the highest altitude of the rock glacier,
width; length; aspect; slope; form ratio defined as length/
width. It was scheduled also the topographical location of
the rock glaciers and the litology of the bedrock outcropping
around the landforms.
The lowest altitude of the active rock glaciers, that could
be used as the lowest boundary of the mountain permafrost
ranges from 2850 to 2150 m a.s.l. with a mean value of
2537 m a.s.l. This altitude corresponds to a mean annul air
temperature of about -1.3 °C. The mean value of the lowest
altitude for the inactive rock glaciers is 2108 m a.s.l, but
we think that is not correct to use this one as indicator of
the relict boundary of the mountain permafrost: according
to our field studies in fact, the inactive landforms can be
aged very different. The morphometric parameters indicate
that the widespread form is lobate (ratio L/l=2); the
mean length is 535 m, the mean vidth is 326 m; the mean
slope is 27° with a minimum of 2°.
The most part of the rock glaciers is located in a cirque
(44.5 0/0) and this percentage is still greater for the active
forms (60 %); the slope location is widespread in the inactive
forms (50.3 0/0).
The relationship with the glacial pbenomena has been preliminary
approached indicating glaciers, glacierets and perennial
snow banks near the rock glaciers: only the 2.60/0
of the rock glaciers is close to a glacier meanwhile is more
frequent the occurrence of perennial snow banks or glacierets
around the rock glaciers (20 %).
Also the lithology of the bed rock is a significant factor: in
fact more than the 760/0 of the rock glaciers in the Lombardy
Alps overlies on metamorphic bedrock. The distribution
of the rock glaciers in this region appears strongly
conditioned also by the aspect; in fact more than the 60 0/0
of these landforms is located on the northward slope (NW
to NE).
On the basis of our field observations and of the remote
sensing analysis we can suggest moreover some other significanttopics:
- in the Lombardy Alps the rock glaciers are the most important
indicators of mountain permafrost, but permafrost
occurs also in correspondence of other landforms not necessarily
of periglacial kind;
- for permafrost mapping is probably more correct to
classify the rock glaciers on the basis of the relationship
between thickness of the active layer and the present climatic
conditions;
- a very promising method for mountain permafrost mapping
is the remote sensing mapping integrated with field
observations and measurements collected in a data-base.
The relationship between the holocenic glaciers evoluton
and the rock glaciers distribution and the importance of
the lithology for the formation of the rock glaciers and for
the permafrost thermal evolution will be certainly the two
most important topics for the future research in the Lombardy
Alps.
YANNI GUNNELL 1 & ANDRE LOUCHET 2
Plate tectonics, erosion cycles and structural predesign, A
tentative synthesis for southern India and Sri Lanka
1 Laboratoire de Geographie Physique, Cnrs-Ura 1562, Universite
Denis-Diderot, 2 Place Jussieu, Case 7001,75005 Paris, France
2 Institut de Geographie, Universite Paris-Sorbonne,
191 Rue Stjacques, 75005 Paris, France
With the improvements of radiometric dating and offshore
sediment stratigraphy, geomorphological research is increasingly
involved in reapparaising theoretical models of
continental landscape development.
Indian and Sri Lankan planation surfaces have recurrently
been dealt with as «stratigraphic» markers to bracket denudation
chronologies, but these need to be reinterpreted
in the light of our contemporary understanding of plate
tectonics. The present study incorporates apatite fissiontrack
data from southern India to monitor the response of
the South Indian shield to tectonic impulses of change.
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