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Evolution of a deep-seated rock mass movement observed with satellite SAR interferometry

Tazio Strozzi(1), Urs Wegmüller(1), Eric Perruchoud(2), Reynald Delaloye(2), Andreas Kääb(3) and Christian Ambrosi(4)

(1) Gamma Remote Sensing, Worbstrasse 225, 3073 Gümligen, Switzerland
(2) University of Fribourg, Ch. du Musée 4, 1700 Fribourg, Switzerland
(3) University of Oslo, Postbox 1047 Blindern, 0316 Oslo, Norway
(4) University of Applied Sciences of Southern Switzer, P.O. Box 72, 6952 Canobbio, Switzerland

Abstract

The displacement of an unstable slope in the Aletschwald region (Canton of Valais, Switzerland) has been observed between 1992 and 2007 with satellite SAR interferometry. Analysis of ERS-1, JERS, ERS-2, ENVISAT and ALOS differential SAR interferograms revealed an acceleration of the movement. The ERS-1 / ENVISAT-IS2 line-of-sight displacement rate increased from about 3 cm/year at the beginning of the observation period to more than 15 cm/year in the summer of 2007 in the centre of the unstable slope. These values correspond to about 5 cm/year and 30 cm/year, respectively, when projected on the direction of maximum slope derived from a digital elevation model, and are consistent with the rates detected with JERS and ALOS differential SAR interferograms.

The observed phenomenon can be explained by pressure release from the retreating Grosser Aletsch glacier, that has lost in the region of interest 200 m and more of ice thickness since the Little Ice Age (ca. 1850). The deep-seated movement of the rock mass can be well delimited from the differential SAR interferograms as a fairly consistent unit affecting an area of more than 1 km2. However, aerial photography and field observations so far do not disclose the landslide through its surface features, possibly because the displacement is recent, morphological evidences associated to the displacement are masked by moraines, and sparse forest is largely covering the area. Differential GPS measurements, matching of repeat air photos, and further aerial photography interpretation are ongoing to complement the differential SAR interferometric analysis, which will be extensively presented in this contribution.

 

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry