Gravitational slope deformation in the western Swiss Alps: characterization, spatial distribution and implication for recent mountain range evolution

Thursday, 18 December 2014: 8:30 AM
Andrea Pedrazzini, Michel Jaboyedoff and Florian Humair, University of Lausanne, Lausanne, Switzerland
The influence of Gravitational Slope Deformations (GSD) on mountain belts’ erosion rate has been identified worldwide and more particularly in valleys that were affected by quaternary glacial retreat. However, owing to the lack of comprehensive identification of the predisposing factor influencing their spatial distribution, size and failure mechanisms, their effective impact on the landscape evolution remain difficult to quantify. In this contribution, we present the first regional-scale detailed GSD inventory of the entire upper Rhone catchment (Western Switzerland). The detection and mapping of GSD are performed by combining different remote sensing approaches. Moreover, a detailed characterization of the different inventoried events is proposed, taking into account their geometry, morphology and failure mechanism. Based on these analyses, more than 300 GSDs, corresponding to 11% of the entire study area, are identified. Spatial and statistical analyses highlight that GSDs are not uniformly distributed within the study area but that six clusters, encompassing more than 80% of the detected instabilities, can be highlighted. Our investigations demonstrate that the GSD clusters are mainly related to the coexistence of active tectonic processes (including high uplift gradients and seismic activity), large scale brittle tectonic weakness zones and high local relief. In addition, climate forcing is also identified to influence the distribution of GSD, via relief creation and in particular by the formation of overdeepened areas operated by glaciers during LGM. Conversely, lithological and structural conditions appear to primarily control the failure mechanism and the size of the detected GSDs but do not influence their spatial distribution. The strong impact of active tectonic processes on GSD distribution suggests that its effective role needs to be revaluated in order to better understand and quantify post-glacial erosion rate.