Item: Field tests of snow stability
Title: Field tests of snow stability
Proceedings: Proceedings of the 1980 International Snow Science Workshop, Vancouver, BC, Canada
Authors: Chris J. Stethem, Avalanche Consultant, Whistler, B.C. and John W. Tweedy, Rossland, B.C.
Abstract: Snow stability evaluaton is a critical element in avalanche hazard evaluation. The procedure of stability evaluation encompasses an analysis of avalanche activity, snow cover distribution, snow stratigraphy, and meteorological data. The objectives of this study were to develop field tests of snow stability which can be used as input data in stahility evaluation for avalanches or as direct tests of snow stability. The tests were applied on Whistler, Blackcomb, and Granite mountains in study plots representative of the avalanche starting zones. Whistler and Blackcomb mountains are located at Whistler, B.C. in the centre of the South Coast mountain region. The climate here is of a mild, moist type typical of West Coast mountain regions. Granite Mountain is located at Rossland, B.C. in the West Kootenay district of the South Columbia mountain region. The climate here is of the cool, moist type typical of the interior highlands. Observations taken in the study plots were correlated with time and type of avalanche occurrences, depth of slab fractures, and observations of snow structure at avalanche fracture lines. Study plot observations included the shear frame test, the shovel shear test, the ram profile :test, and the tilt column test. Ram profiles were taken through the weak zone of the snowpack using both the standard Haefeli ram penetrometer and a lightweight ram penetrometer. Snow crystal forms and temperatures were observed in the critical layers. The ramsonde data is not discussed in this report. Dynamic penetration of the heavy 1 kg ram causes it to pass through the surface of the snow cover which often contains critical failure planes. The 0.1 kg lightweight ram yields a complex illustration of the new snow cover which is fairly difficult to interpret. During a portion of the study period, the tilt column test was also employed. It was found to be a time consuming duplication of the shovel test and it was discontinued.
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Keywords: snow stability, hazard, sheer frame test, shovel shear test, avalanche control
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