Maximum frontal speeds, alpha angles and deposit volumes of flowing snow avalanches

Approximate maximum frontal speeds from 89 snow avalanches were analyzed to yield probabilistic estimates of maximum speed scaled with path length parameters. In addition to speeds, 88 companion values of runout for the events in terms of the alpha angle (tanα = H0/X0 : total vertical drop/total horizontal reach) as a simple index of runout were analyzed and compared to the estimated frontal speeds. The results showed alpha angle decreases with maximum frontal speed but with wide scatter. Size estimates for 68 of the avalanches were obtained consisting of final deposit volumes. Correlation between speed and alpha angle measurements showed speed increases with size and alpha angle decreases with size. The probability estimates provided contribute to the definition of the design avalanche for a given avalanche path.