Extreme avalanche runout in space and time

The distribution of avalanche runout varies in space and time for individua l avalanche paths and from mountain range to mountain range. In this paper, such variations are considered based on the assumption (supported by data worldwide) that the spatial distribution of extreme avalanche runout follow s a Gumbel distribution and that the arrival rate of avalanches can be mode lled as a Poisson process. The input required is a set of extreme avalanche runout distances for the mountain range and a knowledge of avalanche frequ ency at the beginning of the runout zone for the path in question. Such inf ormation allows theoretical estimation of the effective return period as a function of position, which is very important in zoning applications. In ad dition, general expressions are derived to relate Gumbel parameters for dif ferent mountain ranges to a frequency index to explore general frequency im plications from one mountain range to another. The estimated Gumbel paramet ers imply consistent relationships for expected avalanche frequency and ter rain from one mountain range to another.