Issue 11.03 - March 2003

Avalanche! (continued)

To find out how a slope becomes a powder keg, the SLF's Martin Schneebeli spends most of his time watching snow melt - literally. Using a tabletop device called a micro-computer tomograph, he suspends lipstick-sized samples of snow inside a cylinder the shape of a soup can. The sample rotates slowly along its vertical axis as the machine takes grain-thin (25- to 80-micrometer) density readings. Scanning the sample takes eight hours. Then Schneebeli tweaks the heat source and repeats the entire process; often, he spends 30 days observing the same piece of snow. "We always knew tiny differences in weather make huge differences in snowpack stability, but we could never pinpoint what happened," he says. "Now we can actually see the bonds changing between individual grains." Schneebeli (whose name loosely translates from German as "little snow man") also studies larger samples, collected in the backcountry and infused with an acid that preserves the snow's microstructure. Sliced hair-thin, these segments are photographed by a machine designed for large-scale medical biopsies; combining the images yields a 3-D rendering down to the individual bonds. His work is the closest thing to pure science at the SLF - at the earliest, it will start to reveal functioning physical laws within five years.

Eventually, Schneebeli's results will be factored into Snowpack, an SLF software program that simulates how packed layers change during the course of a winter. "Snow is an extremely unpleasant material for modeling," says Michael Lehning, who spearheads the project. "There's settling through condensation, there's recrystallization, there's downward movement of water after melting. In the future, I'd like to add factors like wind-drifted snow and underlying terrain." Pulling up his digitally rendered cross-section of a snowpack's predicted composition, the angular German points to blue streaks representing buried hoarfrost: a crystalline layer that forms at the surface when cold nights follow sunny days. Hoarfrost becomes a time bomb under freshly fallen powder, a slick plane that slabs can slide on. Today, Lehning says, there's a 90 percent chance that Snowpack will nail the location of submerged hoarfrost. But that's just a first step. "We're good now at predicting the types of grains that formed within individual layers," he says. "But the big challenge is relating that knowledge to stability within the snowpack."

Sometimes the only way to determine how an avalanche works is to set one off yourself. In 1997, the SLF built a private detonation site in western Switzerland's Vallée de la Sionne. Its bunker there has four concrete hatches that open toward the avalanche slope, revealing digital video cameras, a massive Doppler radar dish, and a large metal tube designed to capture airborne snow particles. Halfway up the mountain, a 70-foot pylon covered in sensors measures the force of descending snow. After a blizzard, a technician detonates explosives high on the slope. The area around the blast shatters like plate glass. The pylon disappears inside a towering flume of powder. At the last minute, the concrete hatches slam shut to protect the instruments. "What happens inside a smaller avalanche does not matter to me," says Betty Sovilla, an effervescent Italian who manages the site. "I'm only interested in the most extreme cases."

Since experiments at Vallée de la Sionne began, Sovilla has had to reconsider what "extreme" really means: The SLF's avalanches displace up to 500,000 cubic meters of snow and ice - the volume of a 25-story building with a footprint the size of a football field. That's roughly five times more than predicted, because scientists and engineers had always underestimated entrainment, the domino effect through which descending avalanches swell in size by tearing up and absorbing all that's underneath.

This data is factored into simulation programs like AVAL-1D, a software package released in 1999 that is now used by countries all over the world, including Chile, Iceland, and the US. The concept is simple: Key in the profile and maximum snow possible for a given slope, then watch a pixelized avalanche sweep onto the terrain below. "Commercializing our simulation programs forces us to turn research findings into something operational," Ammann explains. "We need to be very confident in the simulations. This is life-or-death software." This year, the SLF will release the next version, NewMix, which factors in the greater entrainment and higher avalanche speeds from the Vallée de la Sionne experiments - and will likely enrage alpine property developers as a result. "Not all the old hazard predictions are wrong based on our new data," says Sovilla. "Maybe just 10 percent. But in that 10 percent, people can die."

The SLF's multiple avenues of research might seem only loosely related, but to Walter Ammann they are all elements of a grand design. Unfortunately, that's unattainable until Schneebeli devises the laws to drive it. "Until we understand how grains change and how bonds form," Schneebeli explains, "we won't truly be able to predict the development of the critical weak areas."

In the meantime, riders in Switzerland's teeming backcountry depend on the SLF's daily avalanche bulletin, generated by a team of mountaineering experts using automated weather forecasts and reports from 80 local experts. Last winter, the bulletin drew more than 1.6 million hits online, served up 31,000 faxes, and pushed 30,000 text messages to mobile phones. The bulletin's hardly slope-specific, however, so riders still need a lot of mountain experience to avoid death off-piste.

It will take years - a decade, maybe two - before Schneebeli's days of watching snow melt pay off and Ammann has his seamless model. Perfect avalanche forecasting will require flawless weather prediction. Still, Ammann predicts that "nowcasting" - reading the current safety of a slope - can reach 95 percent accuracy. Standing at the top of a steep descent, snowboarders would be able to enter GPS coordinates and rapidly receive a risk analysis far more likely to save their lives than anything available today. "Even when the people who died were reckless, I can't blame them," Ammann says. "I always ask myself, 'Could we have warned them better?' To me, any avalanche victim is one too many. Even after 10 years, the news hurts every time."

<< Page 1

---------------------------------------------------------------------------

Marc Spiegler (avalanche@marcspiegler.com) is a freelance journalist based in Zurich.

Copyright © 1993-2003 The Condé Nast Publications Inc. All rights reserved.

Copyright © 1994-2003 Wired Digital, Inc. All rights reserved.