Item: Effectively using and interpreting stability tests
Title: Effectively using and interpreting stability tests
Proceedings: Proceedings of the 1998 International Snow Science Workshop, Sunriver, Oregon
Authors: Ron Johnson and Karl Birkeland
Abstract: Determining the likelihood of an avalanche occurring on a given slope is a critical decision faced by both avalanche professionals and backcountry enthusiasts. An important part of that decision-making process is using stability tests and interpreting their results. Though a variety of stability tests are available, we use the rutschblock and stuffblock tests since they both identify weak layers in the snowpack and, to a limited extent, quantify the stresses necessary for weak layer failure. However, there are several limitations to these stability tests, including site selection and interpretation of results, both of which require experience. While site selection may be the most important limitation, we focus on the interpretation of results. Such interpretations can be problematic, since those without the benefit of avalanche experience often latch onto stability test values as an absolute indicator of stability. However, our experience indicates that occasionally dangerous avalanche conditions exist when stability tests show a stable snowpack and that sometimes the snowpack is more stable than , stability tests indicate. In order to partially address the difficulties in test interpretation, we have begun to qualitatively define the quality of the shear failure into three separate categories. This paper will focus on combining the interpretation of rutschblock and stuffblock tests, and describing the shear failure quality, thereby giving useful qualitative field information about the avalanche conditions in a given location. In the end, users must realize that stability tests do not provide a numerical description of the snow stability, but are instead just a piece of the puzzle for avalanche prediction.
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Keywords: snow stability, stability tests, avalanche forecasting, avalanches
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