Direct observations of a three million cubic meter rock-slope collapse with almost immediate initiation of ensuing debris flows
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Date
2020-02-15
Publication Type
Journal Article
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yes
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Abstract
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 × 10^6 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.
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Publication status
published
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Book title
Journal / series
Volume
351
Pages / Article No.
106933
Publisher
Elsevier
Event
Edition / version
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Geographic location
Date collected
Date created
Subject
Rock avalanche; Debris flows; Permafrost; Environmental seismology
Organisational unit
09558 - Walter, Fabian (ehemalig) / Walter, F. ((former))
09599 - Farinotti, Daniel / Farinotti, Daniel
02818 - Schweiz. Erdbebendienst (SED) / Swiss Seismological Service (SED)
Notes
Funding
157551 - Glacial Hazard Monitoring with Seismology (GlaHMSeis) (SNF)
183719 - Seismic investigations of englacial and subglacial environments (SNF)
183719 - Seismic investigations of englacial and subglacial environments (SNF)