The sun is out. The powder is fresh. The slope is clear. Meet the ice men trying to keep you alive on your next killer run.
On a sunny Sunday last winter, two 27-year-old men snowshoed up toward Piz Grialetsch, a serrated peak north of Davos, Switzerland. They were far from the groomed ski trails of the surrounding resorts, and aside from the wind, all they could hear were each other's trudging steps and hard breathing. After spending the previous night in a cabin atop a neighboring mountain, they started the morning with a long snowboard ride downhill. Halfway through the descent, they stopped and began hiking back up the other side of the valley for their final run of the weekend, down the Scaletta glacier to the hamlet of Durrboden through a mile of untouched powder.
Born and raised in the mountains, they knew that route could be dangerous: In 1981, around the same time of year, an avalanche there killed five skiers. But the two men had ridden down from Piz Grialetsch a couple of times that season alone. To be safe, they had stopped to test the snow during their morning run. In an area much like Scaletta - a 40-degree incline facing north - they dug into the snowpack with shovels, examined it for weak layers, and judged it stable. With temperatures rising rapidly, though, the men knew the slope could turn fragile, so they decided to ride one at a time.
The first man launched downhill, his board carving silently through the powder. Suddenly, both of them heard a noise like a bridge cable snapping. Uphill from the rider, a fault line 5 feet deep erupted through the snowpack, and the slope disintegrated into car-sized boulders of ice. According to the police report filed later, the snowboarder disappeared in a massive cloud of white as his companion watched, helplessly, from above. For a moment, the rider reemerged. Then the fault line extended, more of the mountain slid down, and he vanished again.
Perhaps he screamed, but just a foot of snow will muffle any sound. Within seconds, the avalanche had roared a mile downhill, leaving behind a crater the size of Times Square. The man on the ridge scrambled after his friend, tracking the signal from the radio transceiver the trapped rider wore, and within minutes dug him out from under 5 feet of snow. But he uncovered only an asphyxiated corpse.
From a kinetic standpoint, any snowy slope steeper than 35 degrees has the stability of a fleet of 18-wheelers suspended by fishing line over a layer of bowling balls. An ounce too much pressure in the wrong spot at the wrong moment and the entire structure comes down in a catastrophic crescendo. Immediately after a heavy snow, powder avalanches can storm downhill. Once the fall compacts, slab avalanches, like the one below Piz Grialetsch, can unleash tons of snow and ice. Finally, when spring melt moistens the pack, flow avalanches can steamroll downhill like white mud slides. Often, just hours before an avalanche destroys a slope, you'd be safe racing down it with a team of polar bears.
Like hurricanes, forest fires, and floods, avalanches arise from known meteorological conditions. Unlike those disasters, though, avalanches cannot be tracked as they swell, since they start, strike, and subside in mere minutes. The internal physics of even a stable slope are poorly understood. Resting on a mountain, snow seems inert, but its microstructure mutates constantly. Individual crystals rapidly bond to each other; unlike a sand dune composed of discrete grains, the snowpack functions as a sintered mass, its structural coherence dependent upon millions of tiny bonds. Over time, gravity pulls the entire mass downward, often causing the top sections to shear loose, since they're unhindered by friction with the terrain. Depending on the type of crystals that compose adjoining layers, they can fuse perfectly or slip over one another like greased glass. Heat from the sun above or the earth below courses through microscopic air pockets, weakening the bonds. "Snow is just so complex in terms of the processes affecting its structure," says Bob Brown, who studied avalanches for 30 years at Montana State University. "When I worked on the Apollo space program, I thought rocket science was the hardest form of physics, but snow science is even harder."
The premier center for avalanche science is Switzerland's Institute for Snow and Avalanche Research (commonly known as SLF, its German abbreviation), located in a rustic two-story building in Davos a few miles from Piz Grialetsch. Founded by the Swiss military in 1937, the snow institute is now a branch of Zurich's Federal Institute of Technology, the MIT of Europe, and its subject is studied on a scale that runs from minute to mega. A 100-foot-long "snow slide," riddled with radar detectors, charts the action with millisecond precision. A wind tunnel tracks how individual snowflakes move, critical because gusts can deposit heavy drifts on already fragile slopes. Each winter, the institute detonates test avalanches in a private valley in western Switzerland. "The SLF is the world's top avalanche research outfit, because it works more broadly than anyplace else," explains Bruce Jamieson, an adjunct professor of geophysics at the University of Calgary. "It tackles all the tough problems, and it isn't limited to projects that show results in a year or two."
Since 1992, the institute has been led by Walter Ammann, a wiry 53-year-old civil engineer who himself skies the backcountry. "We have a lot of natural scientists here, but we don't do ivory-tower work," Ammann says. "We want to help the people living in the mountains and doing alpine sports." Ammann's resolve intensified in 1994, when his best friend from childhood was killed by an avalanche in Disentis, near where they grew up. "His death didn't change my work," Ammann says, "but it surely strengthened my will to have a public impact."
Fatalities occur often in Switzerland, a country dominated by the Alps. Hundreds of thousands of the country's citizens live in areas where avalanches can affect their daily lives. Swiss law requires that every mountain settlement be mapped by engineers into avalanche zones. Construction is forbidden within red zones, while buildings in blue zones must include reinforcements or other defenses. As with any zoning, politics come into play. In the Swiss village of Evoléne, recalls former SLF staffer Urs Gruber, "the locals kept saying, 'Don't listen to these stupid theoreticians. There's never been an avalanche in the red zone they drew - the buildings there are hundreds of years old.'" Then, in 1999, an avalanche crashed through the town, destroying 39 buildings and killing 12 people.
Right now, many ski domains make avalanche risk assessments by observing weather conditions and using the SLF's Nearest Neighbor software, which digests regional conditions and spits out avalanche patterns for the 10 most meteorologically similar days on record. Running on everyday PCs in ski domains as far away as Utah and Kazakhstan, Nearest Neighbor offers statistically sound predictions for the likelihood of disaster. But it's only as good as the data available, and it's useless in cases when there aren't enough similar days.
Ammann envisions a more scientific solution. Over the past decade, researchers studying hurricanes have abandoned so-called black-box regression analysis in favor of computer simulations. Ammann wants to do the same thing for avalanches: build a complete, seamless model that encompasses the entire gestation of an avalanche, from new-fallen flakes to mutating layers to thundering slabs. Although he has the processing power to handle the number crunching, he's still awaiting the scientific principles that would drive it.
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."
