Slip rates variability and sediment mobilization on a shallow landslide in the northern Swiss Alps

Abstract

Geomorphic and morphometric data imply that process rates of the Schimbrig landslide, located in the Entle watershed (Central Switzerland), are still limited by the elevation of the LGM base level. At present, the Entle watershed is in a stage of adjusting to the lowered post-glacial base level as indicated by knick zones in the trunk stream. Some thousands of years later when these knick zones will reach the Schimbrig site, we anticipate a substantial increase in process rates and sediment flux for the landslide.The pattern of slip rates was measured on the Schimbrig landslide over a 14-months period. We propose that a Bingham plastic model explains much of how measured slip rates are linked to the observed topography, climatic variations and thickness variability of the landslide mass. This model explains why slip rates have been highest where the thickness of the material is substantially higher. It also explains why slip rates are highest in late summer/autumn and early spring. It appears then that snow melt in spring and decreasing temperatures in late summer/autumn potentially result in a high retention of the pore water and thus in a low viscosity of the material, which, in turns, promotes slip rates. Interestingly, an extreme rainstorm like the one of August 2005 only had a local impact on the landslide mass by triggering small scale earth flows and debris flows. This implies that the earth slide material does not directly respond to an episodic pattern of rainfall. Such precipitation events, however, superimpose a smaller-scale imprint on the landslide relief.

Spatial statistical modeling of shallow landslides—Validating predictions for different landslide inventories and rainfall events

“…3a) that was overthrusted 15-25 km northwards and uplifted. shaped by glacial erosion with moraines and fluvial deposits (Schlunegger, 2006;Schwab et al, 2007). The elevation ranges from 820 to 1680 m, and the distribution of the slope angles has a mode at about 30° (Fig.…”

Unravelling earth flow dynamics with 3-D time series derived from UAV-SfM models

“…Seasonal slip rate variability of the area has been determined by Schwab et al (2007) based on GPS measurements over a period of 14 months between 2004 and 2005. Slip rates were more intense in early spring and late summer and ranged between 0.1 and 0.25 m month −1 .…”

“…For further surveys of the Schimbrig earthflow, our workflow has to be adapted to include direct georeferencing. In this case study, a 1-year time interval between surveys was suitable to capture the internal dynamics of the earthflow (Schwab et al, 2007). With respect to this, our 3-D temporal database is considered as dense.…”

“…As such, the very high-resolution topographic reconstructions allow analysis of the spatio-temporal evolution of earthflow-prone terrain, as well as going beyond conventional survey methods and expert knowledge (Savi et al, 2013;Schwab et al, 2007Schwab et al, , 2008. Savi et al (2013) provide a historical insight into the Schimbrig sliding activity based on dendrochronology over the last 150 years.…”

“…These qualitative data on hillslope processes provide information on surface displacements that extends beyond the time span of photogrammetric techniques, but the temporal information has its limits regarding quantitative and continuous data on displacement rates. A first attempt to quantify slip rates of the earthflow was carried out by Schwab et al (2007), who tracked control points using GPS measurements. However, we are now able to compute slip rates over the entire extent of the earthflow at very high temporal resolution applying image correlation algorithms to very high-resolution aerial images.…”