International Snow Science - Montana State University Library

Item: Melt-induced deformation in an isothermal snowpack

• • Title: Melt-induced deformation in an isothermal snowpack

    Proceedings: Proceedings of the 2004 International Snow Science Workshop, Jackson Hole, Wyoming

    Authors: Simon A. Trautman1, Stephan G. Custer1, Karl W. Birkeland 1,2 1Dept. of Earth Sciences, Montana State University, Bozeman, MT 59717 USA 2U.S. Forest Service National Avalanche Center, P.O. Box 130, Bozeman, MT 59771 USA Contact: simont@montana.edu

    Date: 2004

    Abstract: Bridger Bowl Ski Area outside of Bozeman, MT, USA, has encountered annual problems forecasting large, wet loose avalanches that occur during warming events in the spring. These avalanches terminate within the ski area boundary and create a potential hazard to skiers and equipment alike. A study is being conducted at Montana State University in order to further understand wet snow processes the Intermountain Climate Zone and their relation to melt-induced avalanche activity. We believe that creep plays a significant role in wet-loose avalanche events. This poster discusses methods employed in the documentation of creep in the Bridger Range, as well as the timing and rate of deformation in March and April of 2004. During the spring of 2003, sawdust filled boreholes showed accelerated downslope movement near the surface of the snowpack. The depth of accelerated motion was similar to the depth of melt-water accumulation and surficial instability. In March of 2004 we used an array of string potentiometers in an attempt to quantitatively document creep during melt events. Preliminary results show snow moving differentially at three levels in the snowpack, with the highest velocities being near the surface, and the lowest being near the ground. The maximum velocity logged throughout the period is ~1.0 cm/day, while glide rates ranged from 0 to 3mm/day. Borehole excavations show that in an isothermal snowpack, surficial melt layers deform at rates higher than in underlying snow and that stratigraphic boundaries such as ice layers can control local rates of deformation.

    Presenters: Unknown

    Keywords: loose avalanche, hazard, deformation

    Subjects: snowpack bridger bowl ski area wet avalanches

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