Item: Occurrence conditions oftwo catastrophic avalanches at chamonix, france
Title: Occurrence conditions oftwo catastrophic avalanches at chamonix, france
Proceedings: OCCURRENCE CONDITIONS OFTWO CATASTROPHIC AVALANCHES AT CHAMONIX, FRANCE
Authors: Franyois RAPIN and Christophe ANCEY, Cemagref, France
Abstract: In February 1999, in Chamonix, France, a large avalanche destroyed 14 houses and killed 12 people in a village called Montroc and another flowed through a large stopping system (Taconnaz avalanche path). After presenting historical and meteorological data, the paper focuses on describing the main effects (trajectories, destructions) of the dry-avalanche flows and the consequences in terms of hazard zoning or protective measures. Depending of the chosen parameter (snow fall, snow height in the starting zone, runout distance), the return periods of these events ranged from 5 years to more than 100 years. Although the point can be still debated, our opinion is that these two avalanches were dry-snow avalanches, with most of the mass near the ground. Using two different approximate dynamic models (Voellmy and powder snow) allowed us to compute different physical parameters (heights, speeds, pressures). The effects of the rising slopes (because of the opposite mountain side or of high catching dam) in the last course part are taken into account. In terms of mitigation measures, comparison of the two different methods, (new zoning for Montroc and extension of the protection system for Taconnaz) illustrates difficulties (technical, legal, and social) encountered by public officials.
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Keywords: avalanche, mitigation, chamonix
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