Thursday, February 13, 2014

Avalanche Clip

Came across this rather unusual video of an avalanche. The avalanche shown starts off in the typical billowy pattern of snow rushing at high speeds down a steep mountain slope but then morphs into a rather unique ice movement that is highly destructive.

While avalanches do kill too many people in Washington State, most of the hazard is in the back country in areas where cross-country skiers, snowshoe, and snowmobile enthusiasts enter risky areas. The mountain passes and ski areas are routinely monitored and purposeful avalanches are triggered to greatly reduce the risk. In he case of the passes over the North Cascades and Cayuse Pass that hazard is reduced by simply shutting  the passes for the winter.
I have had only one project in Washington State that involved avalanche hazards to home sites. The site was identified as an alluvial fan hazard area. I began the assessment with the idea that the hazard was debris flows down a stream channel. A review of areas on ground of the fan and up the stream did not fit the debris flow model, but infrequent avalanches did. I was not able nor was it necessary to work out a potential frequency of the event. The avalanche shown in the video would have a very low frequency, hence the houses. But that is the nature of hazard assessment - thinking in terms of worse case scenarios.

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