24 February 2020
The giant Kandersteg rock avalanche in the Bernese Alps in Switzerland
In a paper just published in the journal Landslides, Singeisen et al. (2020) provide a very comprehensive analysis of the landslide, including the deployment of a new set of dating methods to try to ascertain the timing of the failure. The description of the landslide is impressive – it started as a planar rockslide high on the mountain side. The authors estimate that 750 to 900 million cubic metres of limestones sandstones detached along pre-existing discontinuities from the northwest face of the Fisistock peak. As the image above shows, the landslide descended a very steep slope into the valley below – the schematic diagram below, from Singeisen et al. (2020), provides some details of the geometry of this part of the landslide:-
The large descent into the valley caused the rock mass to fragment, forming a rock avalanche that traveled northwards along the valley, during which time it entrained sediments from the valley floor. By the time the landslide stopped moving it had increased in volume to about 1,100 million cubic metres – i.e. 1.1 cubic kilometres. The landslide traveled a total distance of about 10 km, as the map from the paper below shows. The source zone of the landslide is the red area highlighted in the southeast corner of the map, whilst the landslide deposit is outlined in purple:-
The map above provides some of the dates from the research. Singeisen et al. (2020) suggest that this failure occurred about 3,200 years before the present. Of course it is hard to know what might have triggered this landslide, but the authors note that there is a cluster of large Alpine landslides with dates from about this time. There is some evidence that this was period in which glaciers advanced and conditions were wetter. However, giant landslide may collapse through progressive failure rather than triggering, so such interpretations are inevitably uncertain.
Singeisen, C., Ivy-Ochs, S., Wolter, A. et al. 2020. The Kandersteg rock avalanche (Switzerland): integrated analysis of a late Holocene catastrophic event. Landslides. https://doi.org/10.1007/s10346-020-01365-y