Item: Snowpack temperature and decreases in tensile strength
Title: Snowpack temperature and decreases in tensile strength
Proceedings: Proceedings of the 1998 International Snow Science Workshop, Sunriver, Oregon
Authors: R. S. Rosso, D. Howlett, S. Calhoun, Alta Ski Lifts Co, Alta, Utah
Abstract: In an effort to understand post-control and other natural avalanches that occur shortly after rain begins or the sun's rays start to warm the starting zone, several experiments were conducted. The use of inexpensive, commercially available data-loggers for in-situ temperature data acquisition and recording is presented. By monitoring the snowpack temperature at various depths we found warming from the sun to reach as deep as 50 cm within hours after the sun's rays reached the slope. At shallower depths the sun's radiation warmed the snowpack (not just the surface) to temperatures well above the air temperature much more rapidly. Under conditions artificially created to simulate rain, the snowpack temperature was found to increase at depths of as much as 20 em as the rain crust froze on the snow surface above. Finally, by conducting in-situ tensile strength tests on the upper snow layers during simulated rain we found average decreases in snow strength of 15% to 30%. We theorize that a snow slab over an extensive weak shear layer that is being supported mostly by the slab tensile strength could fail as it warms within a brief period of time after the onset of the sun's radiation or a rain event.
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Keywords: rain-on-snow, snow temperature, snow strength
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