Baron, L.

Lambiel, C.

Marescot, L.

Reynard, E.

Scapozza, C.

Serveur académique lausannois

                     Thermal State of Frozen Ground in a Changing Climate During the IPY Abstracts from the  Third European Conference on  Permafrost 13-17 June 2010                    Thermal State of Frozen Ground in a Changing Climate During the IPY  Abstracts from the  Third European Conference on Permafrost 13-17 June 2010 Editors: Jordan R. Mertes, Hanne H. Christiansen and Bernd Etzelmüller           Published by The University Centre in Svalbard ISBN: 978-82-481-0010-2               Cover page picture: Reindalen Pingos Svalbard, Norway, April 20, 2010 Jordan R. Mertes Distribution and Structure of Permafrost in Two Alpine Talus Slopes, Valais, Swiss Alps C. Scapozza1, C. Lambiel1, L. Baron2, L. Marescot3 & E. Reynard1 1Institute of Geography, University of Lausanne, Lausanne, Switzerland 2Institute of Geophysics, University of Lausanne, Lausanne, Switzerland 3Risk Management Solutions (RMS), Zurich, Switzerland 1 INTRODUCTION AND STUDY SITES In order to determine the spatial extension and the characteristics of the permafrost within alpine talus slopes, geophysical measurements were carried out in several sites of the Swiss Alps, proposing a model of the permafrost distribution in talus slopes located within the Alpine periglacial belt (e.g. Lambiel and Pieracci, 2008). According to this model, permafrost appears likely in the lower part of the slope, whereas it is generally improbable upslope. In order to vali-date this model, two periglacial talus slopes located in the western part of the Swiss Alps (Valais) have been studied thanks to destructive borehole drilling and electrical resistivity tomography (ERT) profiles: Les Attelas talus slope, composed of paragneiss, (Verbier area, 2600-2800 m a.s.l.) and the Petit Mont Rouge talus slope, composed of dolomites and limestone (Arolla area, 2600-2700 m a.s.l.). 2 RESULTS AND DISCUSSION Three boreholes have been drilled along an upslope-downslope transect in the two talus slopes. For both sites, frozen sediments are present only in the two lowest boreholes, whereas the upper borehole does not present ice (Fig. 1 – for more details, see Scapo-zza et al., submitted). The stratigraphy is confirmed by ground temperatures registered in the boreholes. In both sites, an upslope-downslope ERT profile has been measured in summer 2009. These two profiles show a difference in inverted resistivities between the lower and the upper part of the slope. In the At-telas talus slope, a resistive body with values higher than 15 kΩm (with maximal resistivities higher than 50 kΩm) and a thickness of about 15-20 m is present in the lower part of the slope, with resistivities that decreased with increasing elevation. In the Petit Mont Rouge talus slope, maximal resitivities are comprised between 100 and 200 kΩm in the lower part of the talus slope (between 54 and 82 m), and higher than 200 kΩm in the protalus rampart (be-tween 88 and 116 m). In the uppermost part of the profiles, the resistivities are lower than 5 kΩm for the Attelas talus slope, and lower than 15 kΩm for the Petit Mont Rouge talus slope. These results confirm that, in the two studied sites, the presence of permafrost is probable in the lower parts of the talus slope, whereas it appears to be im-probable in the upper parts. The borehole data al-lowed validating the stratigraphy obtained from the ERT profiles, both for the distribution of frozen sediments in the talus slope and for the depth of the detected structures.    Figure 1. Inverted ERT profiles and boreholes with stratigra-phy along an upslope-downslope transect. References Lambiel, C., Pieracci, K. 2008. Permafrost distribution in talus slopes located within the alpine periglacial belt, Swiss Alps. Permafrost and Periglacial Processes 19: 293-304. Scapozza, C., Lambiel, C., Baron, L., Marescot, L., Reynard, E., submitted. Internal structure and permafrost distribution in two alpine periglacial talus slopes, Valais, Swiss Alps. Geomorphology. Third European Conference on Permafrost 158

Distribution and structure of permafrost in two alpine talus slopes, Valais, Swiss Alps

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Distribution and structure of permafrost in two alpine talus slopes, Valais, Swiss Alps

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