Inter-Party Avalanche Involvements May Increase Quadratically With Party Density

We estimate, from first-principles, the rate of inter-party avalanche involvements. The model suggests that the likelihood of inter-party involvements is quadratic in the density of parties -- twice as many parties quadruples the likelihood. The model predicts that when the product of the party-density and the area of a day's potential avalanches approaches one, inter-party avalanche involvements will become a substantial fraction of all avalanche involvements. As a corollary, the relative rate of inter-party involvements is expected to increase with avalanche size. We argue, with selected North American inter-party incidents from 2001-2019, that inter-party involvements are a timely concern. To spur conversation, we enumerate a variety of strategies that may mitigate inter-party hazard.