White death

Slide into oblivion
Avalanches unveiled
Rotten snow
Avalanche forecasting
Staying safe
Anatomy of a snowflake

 
This slide, in Big Cottonwood Canyon, Utah, killed one person.

Photo by Neil Ryland. Courtesy Westwide Avalanche Network.
















 
















Avalanche-busters shoot towards an overhanging cornice at Alyeska's Glacier Bowl. Alyeska, Alaska.

Courtesy Westwide Avalanche Network.

 
A slab avalanche is visible in a mountain bowl behind a 'Closed: Avalanche Danger' sign. Slide with pride
If you've read descriptions of being at the mercy of tumbling snow, you've probably figured out that avoidance is the only intelligent approach to avalanches. And a major part of avoidance is making good avalanche predictions. Prediction remains as much art as science, wrote Edward LaChapelle, a godfather of avalanche research who worked at the University of Washington.

"Known physical and mechanical principles of snow behavior provide a qualitative understanding of avalanche origin, but quantitative extension of these principles to specific situations is difficult, for nature presents too many variables to allow exact calculation of snow stress and strength variations with time. The precise time a given slope will avalanche cannot be predicted, but the general degrees of instability in a given area can be estimated with reasonable accuracy."

Translated: We forecasters can help, but you'll still have to watch your buns on those steep slopes...

A key part of avalanche forecasting is evaluating snow, often by digging snow pits and looking for specific weaknesses. Problem is, nobody wants to dig a pit on the steepest part of the slope, and what's true of one location may not be true of another.

Indeed, Richard Armstrong, a snow-and-ice researcher at the University of Colorado, observes that avalanches reflect so many local factors that widely applicable forecasts are questionable.

Three men watch a cannon shooting explosives that disturb the snow and trigger avalanches before skiers arrive. "You might be able to do a very good job of developing a model for one particular path -- say one that affects a road. But if you're responsible for the entire state, that's a very subjective thing." Nor does an accurate forecast mean that every slope will avalanche, Armstrong adds. "A storm could trigger 20 percent of the avalanches, and the rest are still there, waiting for the next storm..."

No worse than weather forecasting...
Avalanche forecasters like to compare themselves to weather forecasters, who, as Colbeck notes, have a glut of money, data and supercomputers. Colbeck asserts that the atmosphere is transparent compared to snowpack, with its various layers, instabilities, sun exposures and slopes. Combine that opacity with the paucity of avalanche research, and you can predict the result: unpredictability. Still, Colbeck says that since the 1950s, avalanche researchers have made "slow, steady progress. As we learn more about snow physics, develop better instruments for meteorology and measuring snow, better data relay techniques, and better education, we'll get some progress."

So will it ever be possible to predict avalanches with certainty? "I don't see something that will solve this problem," Colbeck says.

That means you'll have to (The horror! The horror!) exercise some judgment...


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