Item: Frictional heating of avalanching, snow and the sintering of avalanche debris
Title: Frictional heating of avalanching, snow and the sintering of avalanche debris
Proceedings: 2002 International Snow Science Workshop, Penticton, British Columbia
Authors: D.A. Miller, E.B. Adams, D.S. Schmidt, and R.L. Brown, US Air Force Academy, Colorado, Montana State University, Bozeman, Montana
Abstract: At the Montana State University Avalanche Research Site, instrumentation has been installed to measure temperatures, flow depth, and velocities during an avalanche. A small shed protects the personnel and data acquisition equipment from the avalanche flow. Five thermocouples have been installed along a 30 meter section of the avalanche running surface. Temperatures along the base of the flow were collected during several avalanches to observe frictional heating. The flowing snow did show a temperature increase as it progressed down the slope, but did not always approach the melt temperature. Snow samples were collected before the tests in the release zone and after the avalanches in the debris. The samples were preserved in the field with isooctane and then transported to the laboratory for examination. A computed tomography (CT) x-ray scanner was used to obtain images of the microstructural details of the pretest and debris snow samples. The CT images showed an increase in grain-bond coordination number when the pretest samples were compared to the debris samples. Using the microstructural parameters from the CT images, the growth ofthe new bonds in the debris was analyzed using a vapor diffusion sintering model. New bonds were shown to grow rapidly at the expense of small high-energy structures that resulted from the avalanche. The analysis showed vapor movement and sintering of new bonds due to surface curvature differences may be the primary debris bonding mechanism in snow that does not approach melt temperatures during an avalanche.
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Keywords: snow and ice, snow crystal, snow crystal growth, snow crystal structure, snow metamorphism, avalanche debris
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