Preliminary experimental evidence of heating at the running surface of avalanching snow

At the Montana State University Avalanche Research Site, instrumentation has been installed to measure temperatures, flow depth, and velocities during an avalanche. Five thermocouples have been installed along a 30-m section of the avalanche running surface. Temperature time histories were collected during several avalanches at the flow running surface. The flowing snow at the running surface did show a temperature increase as it progressed down the slope, but did not frequently approach the melt temperature. Snow samples were collected before the tests in the release zone and after the avalanches in the debris for microstructural comparison. A computed tomography (CT) X-ray scanner was used to obtain images of the microstructural details of the pretest and debris snow samples. Using the microstructural parameters from the CT images, the growth of the 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 a significant debris bonding mechanism in snow that does not approach melt temperatures during an avalanche.