The Element of Surprise

Making sense of a senseless 2011-12 snowpack

Once it pops the fun stops. PHOTOL RE WIKSTROM

A series of natural avalanches covers Highway 210, blocking the path up Little Cottonwood Canyon Road. The Class 2 and 3 torrents rumbled across the road at Black Jack and White Pine Chutes. Fortunately, no one is harmed.

"That night was particularly difficult in that I, and us as a group, significantly underestimated the avalanche hazard," says Utah Department of Transportation's Liam Fitzgerald. "I have learned to expect to be surprised in recreating, personally and in my profession."

That incident and several others like it, depicted the winter in Utah and the Rocky Mountain West during the 2011-12 season. Dealing with the snowpack's unpredictability became an unrelenting challenge last year. But for those responsible for managing mountains, they leaned heavily on the research of the late Monty Atwater and other snow science professionals.

In the 1940s, Atwater was a member of the 10th Mountain Division. He was honorably discharged from the military and landed in Alta to assist the Forest Service as a snow ranger. Atwater's tenacity and patience led to the proliferation of heavy artillery and explosive use in the mountains. He and Ed LaChapelle, the renowned avalanche researcher, author and mountaineer, formed the staff at an avalanche research station at Alta, the first of its kind in the western hemisphere.

Bruce Tremper, the Director of the Forest Service Utah Avalanche Center, has built upon the findings of Atwater and continues to evolve the field of avalanche forecasting and education. "Last year took people by surprise," says Tremper. "It was a completely different animal than they were used to dealing with."
The differences from the previous season were twofold. The overall poor structure of the snowpack made forecasting even more complicated. And second, the average skier was coming off a year where avalanches were scarce, as the conditions had been incredibly stable.

"It was a season of early snowfall followed by long, clear dry spells," says Randy Trover, Snowbird's assistant director of snow safety. "The most difficult part of this kind of year with a faceted snowpack is that there isn't a high level of trust or confidence in what you are doing."

That doubt stemmed from the formation of facets deep in the snowpack, dating to October 2011. The first snow of the year came in strong at the upper elevations, then sat around under intense sun for nearly a month. In early November, the storms returned and laid down a fresh blanket of white gold, covering the few remaining ribbons of snow on the upper mountain. This setup--a slab on top of unconsolidated sugary, faceted snow--is precisely what caused the avalanche that took the life of Jamie Pierre at Snowbird before the resort was open for the season.

The snowfalls that did come in December and January were never profound enough to stabilize the pack and reduce the strong temperature gradients. Tremper likens the depth hoar facets to "a pane of glass ontop of a pile of potato chips." With the right trigger, the whole thing fails, he says.

These failure points were nearly impossible to predict, but the overall pattern seemed to point to shallow trigger points where the snowpack was completely rotten. With the energy stored in the snowpack, fractures were able to propagate great distances, even onto slopes of less than 30 degrees. As Atwater said years ago, "No snow can be called stable which has that miserable stuff in its base."