Abstract
The Säntis nappe is a complex fold-and-thrust structure in eastern Switzerland, consisting of numerous tectonic discontinuities and a range of hillslopes prone to landsliding and large slope failures that modify the topography irreversibly. A slope failure, namely the Sennwald rock avalanche, occurred in the southeast wall of this fold-and-thrust structure due to the rock failure of Lower Cretaceous Helvetic limestones along the Rhine River valley. In this research, this palaeolandslide is examined in a multidisciplinary approach for the first time with detection and mapping of avalanche deposits, dynamic run-out modelling and cosmogenic nuclide dating. During the rock failure, the avalanche deposits were transported down the hillslope in a spreading-deck fashion, roughly preserving the original stratigraphic sequence. The distribution of landslide deposits and surface exposure age of the rock failure support the hypothesis that the landslide was a single catastrophic event. The 36Cl surface exposure age of avalanche deposits indicates an age of 4.3 ± 0.5 ka. This time coincides with a notably wet climate period, noted as a conditioning factor for landslides across the Alps in the mid-Holocene. The contemporaneity of our event at its location in the Eastern Alps provide additional support for the contention of increased regional seismic activity in mid-Holocene.
Highlights
The Sennwald landslide is a rock avalanche associated with the Lower Cretaceous Helvetic limestones in the southeast wall of the Säntis nappe along the Rhine River valley
To address some of these open questions, we introduce a multidisciplinary examination of the Sennwald landslide with mapping of the landslide deposits, dynamic run-out modelling using DAN3D and surface exposure dating using cosmogenic 36Cl as well as an analysis of potential triggers and causes of the landslide
The numerical run-out modelling is performed for the Sennwald landslide using a dynamic simulation modelling software, namely DAN3D, which is generated for mass movements such as landslides and debris flows [71]
Summary
The Sennwald landslide is a rock avalanche associated with the Lower Cretaceous Helvetic limestones in the southeast wall of the Säntis nappe along the Rhine River valley. A toma (i.e., cone-shaped hill) is a typical hill structure at various sizes made of landslide deposits and commonly seen in rock avalanche related events in the Alps [22] Identifying such geomorphological features provides useful information in establishing landsliding patterns on a regional scale. Cross Profiles for the Release and Deposition Areas Previously produced cross section of the landslide deposition area based on borehole data [46] shows earlier depositional environments in the landslide deposition area (Figure 7) These data provide useful information for our understanding of the past landscape and sediment transport dynamics from the hillslope to the valley as well as the impact of landsliding on reshaping the topography. As shown in the geological cross section and indicated in those overdeepening reconstructions, the bedrock in the region of the landslide is 10–50 m below the ground surface
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