Item: High frequency avalanches: release area characteristics and run out distances
Title: High frequency avalanches: release area characteristics and run out distances
Proceedings: 2002 International Snow Science Workshop, Penticton, British Columbia
Authors: Urs Gruber Schmid and Stefanie Sardemann, WSL Swiss Federal Institute for Snow and Avalanche Research SLF, Davos, University of Munster, Germany
Abstract: The motivation of this study was a hypothesis of permafrost researchers, that the occurrence of permafrost is more likely in areas that are usually covered by avalanche deposits and therefore have a retardation of a snow free state. In the past, this phenomenon was modeled by simple average slope and curvature rules that proved to be not precise enough. First, the avalanche database of the region of Davos covering the events of 43 years was analyzed with respect to the avalanche frequency using a Geographic Information System. The release areas of avalanches with a return period of less than two years were identified and characterized using topographic characteristics, i.e. slope, distance to the next ridge, size, curvature and aspect. Then, a two-dimensional numerical avalanche model was calibrated to run out distances of the high-frequency avalanches in the database. As input the determined release areas were used with an initial fracture depth corresponding to the maximum snow cover increase within three days with a yearly return probability. The calibrated values for the friction revealed to have a remarkably higher friction than the ones for extreme avalanches with return periods of 300 years. Based on the parameters found, a procedure was developed to automatically determine the release areas of frequent avalanches and to calculate their run out distances over large regions. The method was then transferred and applied to a permafrost region in the Swiss Alps. The modeled deposition areas were compared to both the permafrost measurements at these places as well as to the currently existing permafrost model PERMAKART.
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Keywords: release area characterization, frequent avalanches, numerical modeling, permafrost
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