Item: Field observations of skier-triggered avalanches
Title: Field observations of skier-triggered avalanches
Proceedings: Proceedings of the 2000 International Snow Science Workshop, October 1-6, Big Sky, Montana
Authors: J. Schweizer and J. B. Jamieson, Swiss Federal Institute for Snow and Avalanche Research, Davos, Switzerland, Dept. of Civil Engineering, Dept. of Geology and Geophysics, University of Calgary, Calgary, Canada
Abstract: Snowpack characteristics for skier-triggered avalanches are described in order to better understand skier triggering, to improve snow profile observation and interpretation, to make suggestions for route selection and to provide a basis for further research. Our analysis is based on field observations of skier-triggered avalanche sites in the Columbia Mountains of Canada and the Swiss Alps. Although these two mountain ranges have different climates the characteristics for skier triggering are similar. The analysis has focussed on slab properties and weak layer properties, and in particular their interaction. The findings support the simple model of skier loading. The slab should preferably be soft to enable the skier to efficiently impart deformations to the weak layer. The slab has to be relatively shallow (50 cm), since the skier's impact strongly decreases with increasing depth. A distinct difference in hardness between the slab and the weak layer causes stress concentrations and favours fracture initiation. Accordingly, when travelling in the backcountry, areas of thinner-than-average snowpack may be potential trigger points, especially when a persistent weak layer exists in the snowpack. Therefore areas of thinner-than-average snowpack are as well the preferred sites for snow profiles and for testing snow stability.
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Keywords: avalanche forecasting, avalanche formation, skier triggering, snow cover stability, physical properties
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