Item: Interpreting snowpack structure
Title: Interpreting snowpack structure
Proceedings: Proceedings of the 1980 International Snow Science Workshop, Vancouver, BC, Canada
Authors: Sue A. Ferguson, Geophysics Program, University of Washington, Seattle, WA.
Abstract: The traditional method of snowpack analysis by construction of a detailed snow profile is tedious, slow, and includes a large amount of data which is not directly relevant to snow slab stability evaluation. This paper suggests reorganizing field procedures by specifically emphasizing those features of the snowpack which are known to be prerequisites for slab avalanches. For example, there are two elements known to be features of all snow slabs: a cohesive slab of snow and a lubricating layer or weak layer over which the slab sits. A third element which must be considered is the bed surface roughness. The snow stability problem, then, becomes one of understanding the relationship between these elements which produce slab avalanches. In a given geographical region there may be only a few basic combinations of these elements which produce the majority of slab avalanches. Thus, it may be possible to greatly simplify the forecasting problem if enough fracture line data are catalogued for the region. Also, it seems possible that simple instrumentation could be developed which could serve to rapidly illustrate the potential instability situations specifically for the above snow slab problem. Figure I provides a possible example. In this case, a wedge is driven down through the slab forcing it to slide over any potential weak layers. Instead of a quantitative measurement of a property of one element of the problem, such as shear frame tests in weak layers, the emphasis here is upon the interaction of the slab and the weak layer as it must occur in some fashion in snow slab release. This test is rapid and is easily performed and interpreted. Such a test procedure, when combined with the previously mentioned simplified stratigraphy catalogue procedures, opens up the possibility that even relatively inexperienced personnel can participate meaningfully in a snowpack stability evaluation at some future point in time. Due to the overall complexity of the problem, however, it is doubtful whether all of the difficult, rare, and subtle cases occurring in a given area could be included. In these cases, the experienced forecaster will be more difficult to replace. Full length paper is available by writing to the author.
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Keywords: weak layer, bed surface roughness, stability, slab avalanche
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