Item: Simple calculations of avalanche risk for backcountry skiing
Title: Simple calculations of avalanche risk for backcountry skiing
Proceedings: International Snow Science Workshop, Davos 2009, Proceedings
Authors: Bruce Jamieson, Jürg Schweizer, Cora Shea, Dept. of Civil Engineering, University of Calgary, Calgary Canada 2 Dept. of Geoscience, University of Calgary, Calgary Canada, WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
Abstract: The avalanche risk from backcountry skiing and its dependence on the regional danger ratings have not been estimated—notably in North America. To get around this data gap, we have tried to calculate the risk using an event tree which breaks the avalanche risk to backcountry skiers into the probability of triggering, the probability of being caught in a triggered avalanche, and the probability of death if caught. An expert survey estimated the probability of triggering a potentially fatal avalanche while making fresh tracks in a trigger zone for each level of regional avalanche danger. A previous study found that 40% of people who trigger a potentially fatal avalanche are caught. Based on accident reports, the probability of being killed depends on the avalanche size, the distribution of which is known for skier-triggered avalanches in Canada. To calculate the daily risk, we modelled making fresh tracks in a specified number of trigger zones as an encounter probability. Based on our assumptions, a person can directly ski a dozen or so trigger zones in a day while the regional danger is Low or Moderate with comparable risk to kayaking. For a person skiing directly 5-10 trigger zones while the avalanche danger is Considerable, the daily risk is likely higher than kayaking and in the range of rock climbing ormountaineering.
Keywords: avalanche risk, backcountry skiing, comparative risk, skier-triggering, regional avalanche danger
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