Friday, February 21, 2014

The Risk of Avalanche

The number and severity of avalanches have been exceptionally high in Colorado this season, especially in the northern and central mountains.  A series of heavy snowstorms, accompanied by high winds, have created conditions that favor the development of these powerful snowslides; unfortunately, a number of fatalities have occurred.

Avalanches occur on slopes that are steep enough to exert gravitational forces on the snow but not so steep that deep snow will not accumulate; in general, that includes slopes with grades of 25 to 65 degrees.  In addition, they are most likely to develop after heavy snowstorms, before the new fallen snow settles and binds to basal layers; windblown snow is especially unstable.  While the typical freeze-thaw cycle helps to stabilize the snow, rapid and dramatic changes in temperature increase its instability.

Though avalanches endanger humans, wildlife and structures, they open swaths in the forest that, in the end, are vital to the health and diversity of the mountain ecosystem.  Those killed in avalanches are generally snow-shoeing, snowboarding or skiing at sites that do not lie within the boundaries of ski areas or parks and where avalanche experts have not had the chance to evaluate and mitigate the risk.  Regional or Statewide avalanche warnings should always be heeded and backcountry recreation should be avoided in the days following a heavy snowstorm.  Of course, it is the occurrence of such storms that often draws those individuals into the mountains; while many are prepared with helmets, shovels and locator beacons, collision with boulders and trees will negate the value of those measures and the only reliable means of preventing injury or death is to heed warnings and avoid high risk terrain.