Item: Measurements of weak snowpack layer friction
Title: Measurements of weak snowpack layer friction
Proceedings: International Snow Science Workshop, Davos 2009, Proceedings
Authors: Alec van Herwijnen and Joachim Heierli, WSL, Swiss Federal Institute for Snow and Avalanche Research SLF Davos, Switzerland. Universität Karlsruhe, Kaiserstr. 12, 76131 Karlsruhe, Germany
Abstract: An essential stage in the release of an avalanche is the propagation of a fracture through a weak snowpack layer. As the fracture propagates, the slab looses its support and comes into contact with the bed surface. In the area of contact, the sliding motion of the slab is constrained by frictional forces. This particular friction process has received little experimental attention until today. Studies on sliding friction have mainly been performed on snow samples composed of small rounded grains in direct contact. In the present study we determine the friction coefficient of weak layers by analysing video records of snow samples sliding down-slope after a weak layer had fractured. The slab and the bed surface are then in indirect contact as the interface consists of the collapsed weak layer. The experiments were carried out in the mountains of British Columbia, Canada, and in the mountains around Davos, Switzerland , between 2002 and 2009. Assuming Coulomb-type friction the initial acceleration of the snow sample is used to determine the friction coefficients. The measurements show an initial friction coefficient on the order of 0.6 and the tendency to decrease thereafter. This is accompanied by the gradual erosion of the interface between the slab and the bed surface.
Keywords: particle image velocimetry, friction, weak layers, avalanche formation
Digital Abstract Not Available