The Kandersteg rock avalanche (Switzerland): integrated analysis of a late Holocene catastrophic event
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Corinne Singeisen I Susan Ivy-Ochs I Andrea Wolter I Olivia Steinemann I Naki Akçar I Serdar Yesilyurt I Christof Vockenhuber
The Kandersteg rock avalanche (Switzerland): integrated analysis of a late Holocene catastrophic event
Abstract In this study, we focus on the Kandersteg rock avalanche in the central Bernese Alps in Switzerland. We achieved an improved understanding of the release and emplacement of the rock avalanche through a combination of detailed field mapping, remote image analysis, reconstruction of deposit and source area volumes, and runout modelling with DAN3D. Based on cosmogenic 36Cl dating of siliceous limestone boulders all across the landslide deposit, we determined an age of 3210 ± 220 years for the event. This age is markedly younger than the previously suggested age of 9600 years. An estimated 750–900 Mm3 of Cretaceous limestones, siliceous limestones (Oehrlikalk, Kieselkalk and Bänderkalk formations) and Tertiary sandstones of the Doldenhorn nappe detached along pre-existing discontinuities from the northwest face of the Fisistock peak. The sliding body fragmented upon encountering the valley floor and the steep opposite valley wall. Next, the dry fragmented rock avalanche propagated northward over a substrate of fluvial sediments. As it moved, the debris became more fluid through entrainment of water and water-rich sediments, until it finally came to a halt 10 km downstream. The final volume of the deposit is estimated at 1.1 km3. Our multi-method approach allowed us to establish that the deposit stems from one colossal event at 3.2 ka and to reconstruct the processes that dominated each phase of the rock avalanche. Our research contributes significantly to understanding not only the Kandersteg event but also complex emplacement processes and mechanics of large rock slope failures. Keywords Landslide . Cosmogenic 36Cl exposure dating . Runout modelling . Kandertal . European Alps Introduction Large slope failures constitute impressive features in mountainous landscapes and are part of the distinctive landscape of high-relief regions such as the Alps (Heim 1932; Abele 1974; Eisbacher and Clague 1984; Hewitt et al. 2008; Fort et al. 2009; Korup et al. 2010; Clague and Stead 2012). Although large-volume (> 10 6 m 3 , Hermanns and Longva 2012) rock slope failures are infrequent, their often catastrophic effects pose a significant hazard to populations and infrastructure in mountainous areas. This is especially true when the mobility of the released material is increased significantly by transformation into debris flows as shown by the recent 2017 Piz Cengalo events in the Swiss Alps (Walter et al. 2020). Rock mass strength, structure and topography are three of the major factors determining the stability of rock slopes (Gerber and Scheidegger 1969; Evans et al. 2006; McColl 2015; Stead and Wolter 2015). The strength of a material is mainly dependent on lithology and the condition and density of discontinuities, and it can be reduced through different processes such as weathering, tectonic a
