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Isabel Schumacher / Departement of Earthsciences / ETH Zürich, Switzerland

Reconstruction of the timing and runout of the Voralpsee landslide, Kanton St. Gallen

The Voralpsee landslide is situated in the Voralpsee valley just between the Churfirsten mountain chain and the Alvier mountains in eastern Switzerland (2'747'476/1'225'159). The landslide created a 30 million m3 deposit that covered the Voralpsee valley over a distance of 3 km. Based on field relations earlier investigators placed the event in the late Pleistocene and assumed a two stage emplacement of the deposit (Keller 19881). The release area is situated at a height of 2042 m a. s. l. at the Chapf peak and is comprised of a 300 m high wall composed of the Tierwis, Schrattenkalk and Garschella Formation. It is thought that the landslide damned the headwaters from the Voralpsee valley and created the Voralpsee lake (1124 m a.s.l.) (Heim 19322, Keller 19881).

The Voralpsee landslide is widely known in the scientific world for its outstanding long runout distance (2 km). However, little work has been done to investigate the time of the event as well as to reconstruct the runout pattern of the landslide. The objective of the master thesis is on one hand to obtain the age of the Voralpsee landslide deposit by surface dating and find out if the deposit was created in one event or several events. And on the other hand, to model the failure and the emplacement of the deposit to find out more about the mechanisms and significant parameters involved in such large rock avalanche. The behavior of rock avalanches is still subject of actual investigation and a lot of open questions remain. The comprehension of the behavior of large rock avalanches is very important as a greater understanding of the mechanisms that lead to such large deposits can contribute to the prevention of the catastrophic effects of future events.

Thanks to the support of CH-Quat I was able to stay 5 days in the Voralpsee valley in July 2020 to map the extent of the landslide deposit and to sample different boulders for surface dating. Thanks so much for the financial support, CH-Quat!

1Keller, O. (1988). Ältere spätwürmzeitliche Gletschervorstösse und Zerfall des Eisstromnetzes in den nördlichen Rhein-Alpen: Weissbad-Stadium/Bühl-Stadium. Geographisches Institut der Universität.
2Heim, A. (1932). Bergsturz und Menschenleben (No. 20). Fretz & Wasmuth.

Isabel Schumacher

I. Schumacher
I. SchumacherImage : S. Ivy Ochs