Wikstrom Jones, K.M., Loso, Michael, Bartelt, Perry, and Vera Valero, Cesar, 2016, Modeled mass and temperature effects of released and entrained snow on the lubricated flow regime of avalanches at Bird Hill, south-central Alaska: International Snow Science Workshop 2016 Proceedings, Breckenridge, CO.
The unpredictable effects of released and entrained snow on avalanche run-out distances make hazard analysis difficult. At Bird Hill in southcentral Alaska, snow entrainment has caused small re-lease volumes (< 25,000 m3) to develop into surprisingly far-running avalanches which endanger a highway and railroad below. In this graduate thesis project, the dynamical avalanche run-out model RAMMS was calibrated and used for the first time in southcentral Alaska. With numerical experiments on a high resolution Digital Elevation Model (DEM), produced with Structure-from-Motion photogrammetry, we examined how mass and temperature of released and entrained snow affected the lubricated wet flow regime and run-out distances. We found that temperature of the released and entrained snow was more critical than mass in determining the flow regime. Meltwater production was the predominant contributing factor to long run-out distances due to reduced basal friction as the avalanche makes the transition from the fluidized to the lubricated flow regime. The temperature of the entrained snow was most important when the entrained mass was large relative to the release mass. Warm (? -1?C) entrained snow in the path made very small -3?C releases warm up quickly and become lubricated. With colder (? -3?C) snow, such releases remained cold throughout the flow and stopped quickly. Monitoring of warming snow cover temperatures in the path is therefore critical for predicting flow regime transitions. The results of this project also showed that terrain features can strongly influence avalanche flow, and that detailed DEMs are therefore important, especially during shallow snow conditions.
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