Open Session - SWISS GEOSCIENCE MEETINGs

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Differentiation of rock avalanche deposits from lateglacial moraines in
Val Ferret (Mont Blanc Massif, Italy) using cosmogenic 10 Be
Deline Philip*, Akçar Naki**, Ivy-Ochs Susan***, Kubik Peter W.**** & Schlüchter Christian**
*EDYTEM Lab, Université de Savoie, CNRS, 73376 Le Bourget-du-Lac, France
(pdeli@univ-savoie.fr)
**University of Bern, Institute of Geological Sciences, Baltzerstrasse 1-3, 3012 Bern
(akcar@geo.unibe.ch, christian.schluechter@geo.unibe.ch)
***Institute of Particle Physics, ETH Hönggerberg, 8093 Zürich (ivy@phys.ethz.ch)
****Paul Scherrer Institute c/o Institute of Particle Physics, ETH Hönggerberg, 8093 Zürich (kubik@phys.ethz.ch)
On September 12th 1717 AD, inhabitants of the upper Ferret valley (Mont Blanc Massif, Italy) witnessed one of the largest
rock avalanches of the Alps, destroying two small settlements with 2 causalities and lost of their cattle. This avalanche
mobilized a rock volume of larger than 10 millions m 3 and huge volume of ice from Triolet glacier. This mass, composed of
ice and sediment, moved more than 7.5 km down valley and reached lower part of the valley. Although this natural hazard
is historically recorded, extend of its deposits in the Ferret Valley is still under discussion due to the insufficient number of
absolute dates.
Quaternary deposits in the upper Ferret valley have been attributed for a long time to glacier advances (Figure 1). In the
1960’s it has been suggested that rock avalanche sediments was forming only a small part of these deposits (e.g. Mayr, 1969).
Later Aeschlimann (1983) argued for lateglacial moraines whereas
Orombelli and Porter (1988) controversially stated that the whole valley was covered by this rock avalanche. Using the new
findings, and relative and absolute ages, Deline and Kirkbride (2008) have recently shown that 1717 AD rock avalanche was
deflected along northern side of the valley floor, preserving older slope and glacial sediments along the southern side
(Figure 1). Moreover, deposits of an earlier rock avalanche onto the Triolet Glacier, probably occurred before 1000 AD, was
also identified (Deline & Kirkbride, 2008). Despite several radiocarbon dates on peat and wood buried in or overlying the
avalanche deposit, the extend of avalanche deposits in the valley floor still remains undetermined, which in fact delimits
the modeling of its propagation.
Our study focuses on the surface exposure dating of Quaternary deposits of Ferret valley with 10 Be. Such exposure dates
would allow us to differentiate these deposits and build up their chronology. With this aim, nine samples from the granite
boulders were collected (Figure 1) and prepared for AMS analysis. The first results of this study will be presented.
REFERENCES
Mayr, F. 1969: Die postglazialen Gletscherschwankungen des Mont Blanc-Gebietes.
Orombelli, G., & Porter, S.C. 1988: Boulder deposit of upper Val Ferret (Courmayeur, Aosta valley): Deposit of a historic giant
rockfall and debris avalanche or a lateglacial moraine? Eclogae Geologicae Helvetiae, 81, 365-371.
Aeschlimann, H. 1983: Zur Gletschergeschichte des italienischen Mont Blanc Gebietes: Val Veni – Val Ferret – Ruitor. Ph.D.
thesis, Universität Zürich, Switzerland.
Deline, P., & Kirkbride, M.P. 2008: Rock avalanches on a glacier and morainic complex in Haut Val Ferret (Mont Blanc Massif,
Italy), Geomorphology, in press. doi:10.1016/j.geomorph.2007.10.020
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Symposium 5: Quaternary Research