Item: Potential release areas and return period of avalanches: is there a relation?
Title: Potential release areas and return period of avalanches: is there a relation?
Proceedings: Proceedings of the 2006 International Snow Science Workshop, Telluride, Colorado
Authors: Margherita Maggioni, Urs Gruber, Ross S. Purves and Michele Freppaz, Di.Va.P.R.A. – Laboratorio Neve e Suoli Alpini, Università di Torino, Italy, WSL, Swiss Federal Institute for Snow and Avalanche Research, Davos, Switzerland, Department of Geogr
Abstract: Avalanche hazard zones are usually defined in terms of impact pressures and run-out distances for avalanches with a specific return period (T). Calculating these parameters through avalanche dynamics models requires a range of input parameters including the extent of the release area, which gives, together with the fracture depth, the total avalanche volume. Today, in Switzerland and Italy release areas for a 30, 100 and 300 year avalanches are assumed to have the same size while fracture depths are varied with T. This paper focuses on the question of whether it is possible to find a reliable relationship between the extent of a release area and the return period. Following the same approach that is used in Switzerland to determine the fracture depth of avalanches, we analyzed with Gumbel extreme-value statistics the relationship between T and the extent of the release area of previously observed events in specific avalanche paths. This study is based on avalanche databases of the regions of Davos, Switzerland and the Aosta Valley, Italy. The results show that for 300yr-avalanches the total extent of the potential release area has to be considered. However, for more frequent avalanches, it is often appropriate to specify only a subarea of the total potential release area. This result suggests that avalanche hazard mapping experts could use the proposed procedure as a help to determine the extent of the release area with a given return period. However, such an approach also emphasizes the need to extend avalanche release area databases by adding new regions and by improving the quality of the release area information collected.
Keywords: avalanche hazard maps, release area, return period, extreme-values statistics
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