Statistical Prediction of Snow Avalanche Runout from Terrain Variables in Colorado

The prediction of snow avalanche runout distance from dynamic equations requires estimates of internal and external friction terms. Previous work indicates a wide variation in the turbulent friction term from 400 to 1800 m sec–2 according to the mean roughness of terrain traversed by flowing snow. Because of the practical difficulties of obtaining parameter estimates for individual slidepaths, an alternative approach to the problem of estimating runout distance is presented. A least-squares regression equation for runout distance is derived from a sample of 67 Colorado avalanche paths with known runout distances. Terrain variables used are starting zone area, longitudinal gradient of the avalanche track, and longitudinal gradient of the runout zone Starting zone area alone accounts for 65% of the variation in runout distance: Track gradient and runout gradient together account for less than 2 percent. A discussion of the physical dependence of runout distance on starting zone area is provided, which supports the results of the statistical analysis.