Slippery science: avalanche prediction still tricky


We've got one month left of prime avalanche season, and in the U.S. there have been 25 fatalities. Here is a vote for no more. Around the West this winter we've had relatively light, late snowfall and fluctuating temperatures; and recent fatalities have led to talk of of this year being especially bad for avalanches. But that's not necessarily true.

Over the past five years, about 30 people have died each year in avalanches. Almost all these fatalities -- about 90 percent -- are triggered by the person who dies or someone in the backcountry with them. 

Geologists, hydrologists and snow researchers have studied avalanche dynamics for decades.  One of the first studies, "Snow Slides and their Causes," dates from 1941, authored by Roy Lundquist, a hydrologic engineer for the U.S. Weather Bureau, but the science really didn't take off a few years later. The title of 'founding father of avalanche science' is generally bestowed upon the outdoorsy skiing enthusiast Monty Atwater. After returning from World War II, well versed in using explosives, he took a job with the U.S. Forest Service and helped found the country's first avalanche research center at Alta, Utah. His book, The Avalanche Handbook, became the gold standard for professionals involved in snow safety. But a scientific discipline never comes to the end of its rope, an, as far as avalanches go, we've still a lot to learn. Last week Science's news site hosted a live chat covering the "Science of Avalanches." 

Professors Tim Garrett and Jim Steenburg, both of the University of Utah, addressed common avalanche questions and spoke of areas within the field ripe for research. "One useful component that might go into improved avalanche prediction models would be snowflake types," wrote Garrett, an atmospheric scientist who measures and models interactions between aerosols, clouds and climate. He and his team have recently deployed a camera system that takes detailed photographs of freefalling snowflakes. (That's right, a snowflake webcam). 

Snow texture plays a large role in creating avalanche conditions. Classically, crystals with long spindly rays, such as the six-pointed Christmas card variety, were thought to interlock and create a sturdier layer than pellet-shaped crystals. This belief is in the process of being tweaked. If covered with a thick layer of snow, classic "plate" type crystals can create a weak layer that can lead to avalanches. "If weather models can improve their predictions of whether it is snowflake or graupel that falls out of the sky, then we might have a basis for improving avalanche prediction," Garrett adds.

Both Garrett and Steenburgh stressed it is hard to assess snowpack stability with certainty and it's best to "avoid generalizations when it comes to avalanche assessment." Snow and atmospheric conditions, recent temperature fluctuations and topography all factor into the complex equation of whether a slide will begin. 

There are some red flags backcountry snow goers should heed, however. If an area has seen avalanches recently, more could be likely. Unstable snow (listen for cracking or collapsing snowpack -- sounds that go "whumpf" or have a hollow drum-like sound), recent heavy snowfall or rain, winds (which load downwind slopes, even when it's not snowing), or recent significant warming can all promote avalanche conditions. Visit to access warning and advisory centers. Wear a beacon, by all means, but try to stay out of harm's path first and foremost. And for pity's sake have a shovel with you.)

While you and I should stay well away, avalanches do have benefits for the landscape. Like fire, they're a means of natural disturbance. Downed trees allow sunlight to reach the forest floor, decay and build soil, and -- if in a stream -- create good fish habitat. The U.S. Forest Service's National Avalanche Center has produced a video (complete with a trippy, jazz-rock soundtrack) exploring the ecological benefits of snowslides. Be safe people.

Danielle Venton is an intern at High Country News.   

1) Image of Monty Atwater with gunner using an avalauncher developed by Atwater, Alta, 1958, courtesy of J. Willard Marriott Library, University of Utah; 2) Snowflake gallery screenshot courtesy of University of Utah Multi Angle Snowflake Camera at Alta Ski Area.

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