High-frequency avalanches: release area characteristics and run-out distances

This study is motivated by 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 modelled by simple average slope and curvature rules that proved to be not precise enough. This study aims to determine the locations of frequent avalanche deposits more accurately using a threefold approach. First, avalanche tracks with frequent avalanche events were located using four long-term avalanche observation data sets. In a second step, the topographic terrain characteristics of the release areas of these frequent avalanches were analysed using a Digital Elevation Model (DEM). In the last step, the run-out distances of these frequent avalanche events were back-calculated with a two-dimensional numerical avalanche model in order to calibrate the model for frequent avalanche run-out distances. As input for the numerical model the determined release areas were used with an initial fracture depth corresponding to the maximum snow cover increase within 3 days with a yearly return probability. The calibrated friction parameters showed 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 modelled deposition areas were compared to both the permafrost measurements at these places and the currently existing permafrost model PERMAKART.