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Direct observations of a three million cubic meter rock-slope collapse with almost immediate initiation of ensuing debris flows

  • Walter, Fabian Laboratory of Hydraulics, Hydrology and Glaciology (VAW), ETH Zurich, Zurich, Switzerland
  • Amann, Florian Chair of Engineering Geology and Hydrogeology, RWTH Aachen University, Germany
  • Kos, Andrew errasense Switzerland Ltd, Buchs SG, Switzerland
  • Kenner, Robert WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
  • Phillips, Marcia WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
  • Preux, Antoine de Marti AG, Bern, Switzerland
  • Huss, Matthias Laboratory of Hydraulics, Hydrology and Glaciology (VAW), ETH Zurich, Zurich, Switzerland - Department of Geosciences, University of Fribourg, Fribourg, Switzerland
  • Tognacca, Christian Beffa Tognacca Gmbh, Switzerland
  • Clinton, John Swiss Seismological Service, ETH Zurich, Zurich, Switzerland
  • Diehl, Tobias Swiss Seismological Service, ETH Zurich, Zurich, Switzerland
  • Bonanomi, Yves Bonanomi AG, Igis, Switzerland
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    15.02.2020
Published in:
  • Geomorphology. - 2020, vol. 351, p. 106933
English Catastrophic collapse of large rock slopes ranks as one of the most hazardous natural phenomena in mountain landscapes. The cascade of events, from rock- slope failure, to rock avalanche and the near-immediate release of debris flows has not previously been described from direct observations. We report on the 2017, 3.0 × 106 m3 failure on Pizzo Cengalo in Switzerland, which led to human casualties and significant damage to infrastructure. Based on remote sensing and field investigations, we find a change in critical slope stability prior to failure for which permafrost may have played a destabilizing role. The resulting rock avalanche traveled for 3.2 km and removed over one million m3 of glacier ice and debris deposits from a previous rock avalanche in 2011. Whereas this entrainment did not lead to an unusually large runout distance, it favored debris flow activity from the 2017 rock avalanche deposits: the first debris flow occurred with a delay of 30 s followed by ten debris flows within 9.5 h and two additional events two days later, notably in the absence of rainfall. We hypothesize that entrainment and impact loading of saturated sediments explain the initial mobility of the 2017 rock avalanche deposits leading to a near- immediate initiation of debris flows. This explains why an earlier rock avalanche at the same site in 2011 was not directly followed by debris flows and underlines the importance of considering sediment saturation in a rock avalanche’s runout path for Alpine hazard assessments.
Faculty
Faculté des sciences et de médecine
Department
Département de Géosciences
Language
  • English
Classification
Geology
License
License undefined
Identifiers
Persistent URL
https://folia.unifr.ch/unifr/documents/308465
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