Field measurements on maximum runout from two different mountain ranges in Canada are presented and compared: the Coast Mountains in British Columbia and the Rocky Mountains. We include a statistical analysis of topographic terrain parameters such as starting zone catchment area, horizontal reach, vertical drop and relevant slope angles. Following McClung and Mears (1991), we derived a dimensionless parameter which is a measure of runout for each avalanche and we found that the runout ratios (defined below) for a given mountain range obey a Gumbel distribution consistent with previous results. In addition, we found that the runout ratios for both mountain ranges have a length-scale dependence which is potentially very important for land-use planning procedures: the mean value of the runout ratio decreases significantly as the horizontal reach increases. Together with data from other mountain ranges, our results show that path length effects will have to be incorporated when using statistical prediction methods for engineering zoning purposes.
The runout ratio is defined as the quotient of two lengths, Δx/Xβ, where Δ is the horizontal distance from the 10° point to the maximum runout position, and Xβ
is the horizontal distance from the start position to the point where slope angle first declines to 10°.