Full-depth avalanche occurrences caused by snow gliding, Coquihalla, British Columbia, Canada

Snow glide is the translational slip of the entire snowpack over a sloping ground surface, and it is thought that rapid rates of snow glide precede full-depth avalanches. The nature of avalanches that release at the ground makes them difficult to predict and difficult to control using explosives. On-slope instrumentation comprised of stainless-steel "glide shoes" was used to measure rates of snow glide for two winters on a bedrock slope adjacent to the Coquihalla Highway, Cascade Mountains, British Columbia, Canada. Climate data and avalanche occurrences were recorded by the British Columbia Ministry of Transportation and Highways. Our results show that the supply of free water to the snow/ground interface by rain or snowmelt is the most important influence on full-depth avalanche release. Full-depth avalanche release responds to rainfall and snowmelt events within 12-24 hours. Occasionally, full-depth avalanches occur unexpectedly during clear, cold periods. Snowmelt by radiation is thought to contribute enough meltwater during these cold periods to induce higher rates of snow glide and full-depth avalanche release. The results also indicate that snow glide alone is not a reliable indicator for full-depth avalanche release.