Item: The spatial variability of snow strength on potential avalanche slopes
Title: The spatial variability of snow strength on potential avalanche slopes
Proceedings: 1990 International Snow Science Workshop, Bigfork, Montana USA, October 9-13
Authors: K.W. Birkeland, R.L. Brown, K.J. Hansen-Bristow
Abstract: (Note: The complete paper is being submitted to the Journal of Glaciology, and only an abstract is provided in these proceedings. Please write to the author to receive a copy of the complete paper.) Since snow avalanches are believed to release from zones of localized weakness, knowledge of snow strength patterns is important for determination of slope stability and for the application of effective avalanche control measures. In this study, the spatial variability of average snow resistance (an index of snow strength) and depth were measured and compared with terrain features on two inclined slopes in Montana during two winter field seasons. An instrument that indexes snow strength by measuring snow resistance was refined (Brown and Birkeland, 1990), allowing the strength of an entire snow slab to be characterized in a short time. The spatial pattern of trees -app,ears to affect the pattern of snow depth at the first site (Figures 1 and 2), where a significant linear relationship was found between snow depth and average snow resistance during both years of study (p-values < 1 X 10-6) (Figure 3). These results suggest that localized snow depth variations may be important in snow strength genesis. Although a linear relationship existed at that site, low r2 values for the two years (r2 < 0.357) indicate additional factors may be critically relevant. A second site with greater cemplexity of terrain features and less localized wind drifting did not show a linear relationship between depth and average resistance. Complicated patterns of resistance at that site demonstrate that many factors contribute to snow resistance. In particular, the snow over rocks was found to have significantly weaker resistance than adjacent areas which were not over rocks (p-value < 1 X 10-6). Results may provide predictive information of weak zone locations in snow slabs, which would improve avalanche forecasting and control techniques.
Keywords: avalanche slopes, snow strength, slope stability, avalanche control
Digital Abstract Not Available