Item: Case study of a deep slab instability and associated dry avalanches
Title: Case study of a deep slab instability and associated dry avalanches
Proceedings: Proceedings of the 2000 International Snow Science Workshop, October 1-6, Big Sky, Montana
Authors: Bruce Jamieson, Torsten Geldsetzer, Chris Stethem, Dept. of Civil Engineering, University of Calgary, Calgary, Alberta, T2N 1N4, Canada, Dept. of Geology and Geophysics, University of Calgary, Chris Stethem and Associates, Canmore, Alberta, T1W2R8, C
Abstract: This study considers the predictive merit of weather and snowpack data for avalanches that released throughout the winter on a layer of faceted crystals that formed on a rain crust in November 1996 in the North Columbia Mountains of western Canada. The facet-crust combinations formed as a result of a cold air mass cooling a layer of dry snow on top of a rain-wened layer. The highly ranked variables associated with natural avalanches include previous avalanche activity, accumulated snowfall over several days, changes in air temperature over four to five days, snowpack properties, including a shear frame stability index, and the difference in hardness between the facet layer and the crust. Increases in air temperature over four to five days correlate with increased avalanche activity, however current theories for warming do not explain decreased stability especially where the slab is thick. We argue that the fractures that release deep slab avalanches may be initiated where the slab is locally thin.
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Keywords: avalanche forecasting, avalanche formation, faceted crystals, snow cover stability, snow cover structure, snow stratigraphy
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