Item: The timing, size, and impact of avlanches on the milford highway, new zealand
Title: The timing, size, and impact of avlanches on the milford highway, new zealand
Proceedings: Proceedings of the 2000 International Snow Science Workshop, October 1-6, Big Sky, Montana
Authors: H. Conway, W. Carran and A. Carran, University of Washington, U.S.A, and Works Infrastructure, TeAnau, New Zealand
Abstract: The timing of direct-action avalanches that threaten the Milford Highway can often be predicted to within a few hours by keeping track of the stress from the new snowfall and the strength of sub-surface layers; avalanching is expected when the stress from the overburden exceeds the strength of a buried weak layer. For operational purposes it is also of interest to determine whether a particular avalanche will affect the highway. A flow model is used to calculate avalanche speeds and impact pressures. Although the model parameters are not well known, observations and model results indicate that the speed of an avalanche usually increases with size. The size of an avalanche depends on the initial depth of failure and subsequent entrainment/deposition of snow as it travels down the path. Avalanches gain mass above the snowline and lose mass before it; the size by the time it reaches the road depends on conditions in the track as well as the depth of the initial fracture. Keeping track of the snowline as well as the cumulative precipitation during storms may prove useful for predicting the size, speed, and impact pressure from avalanches at road level.
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Keywords: snow, avalanches, sub-surface layers
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