Eluding The White Death

By J. MADELEINE NASH

To a seasoned skier, nothing could be more alluring than a descent into a high-country valley carpeted with fresh-fallen snow. And nothing could be more treacherous. The same pristine slopes that offer powder hounds the thrill of carving first tracks can conceal thrills of a more perilous kind: avalanches, known to mountaineers as the "white death." Avalanches have already claimed 19 lives in the U.S. this winter. And last week five Coloradans, who lost their way in a subzero Aspen blizzard, were almost added to that number, raising awareness of the hazard.

"We never doubted we would make it," declared 50-year-old Ken Torp. Along with one companion, Torp fought his way to a trading post after five days in the wilderness. "It was just a question of how ugly and how nasty and how difficult and how uncomfortable it was going to be, and how many fingers we would freeze on the way." The three other lost skiers were found by a search party.

There is no question that Torp and his friends were tempting fate. They set out despite storm and avalanche warnings. During their sojourn, the skiers repeatedly heard the roar of snowslides letting loose. "It was sheer luck they didn't get caught in one," says Doug Bitterman, the avalanche forecaster who posted that day's warnings. Nearly three dozen avalanches rumbled through the area, posing an enormous risk to the rescuers.

For the Colorado Rockies, this has been a season of slides. So far, this winter is shaping up as a record breaker. There have already been 2,260 avalanches, some of them powerful enough to topple full-grown trees. The reason for the surge is simple: big storms have dumped record amounts of snow throughout the Mountain West. Too much snow falling in too short a period sets up the slopes for a slide. The most recent avalanches, for instance, occurred in the wake of a storm that dumped as much as 8 ft. of the white stuff.

Avalanche danger is highest just after a storm because the snow crystals have not had time to forge bonds to one another and to crystals in the existing snowpack. Typically, bonding occurs over a few days' time. Under certain conditions, however, the crystals never bond, but remain loose like a pile of poker chips. This dangerous situation commonly occurs in Colorado, where temperatures are very cold (snow crystals bond most readily close to their melting point). The shape of the crystals is important too. A layer of graupel -- soft hailstones that behave like miniature ball bearings -- substantially increases the avalanche hazard. In essence, graupel provides a high-speed conveyor belt for the layers of snow deposited on top. Another kind of trouble comes in the guise of sugar snow -- coarse grains created when water vapor freezes and refreezes. In Colorado a layer of sugar snow formed early in the season, and has greatly added to the risk.

Once conditions are right, it doesn't take much to trigger a slide. And usually, there is very little warning. "Sometimes you hear a crack like thunder," says U.S. Forest Service research scientist Sue Ferguson, who has been caught in several small slides. "Sometimes the avalanche releases quietly, like rustling silk." Traveling at speeds that can exceed 80 m.p.h., the rushing snowpack compresses the air at its prow, generating a wind blast strong enough to smash windows and hurl skiers into trees. Once the avalanche stops, the snow mass solidifies, entombing its victims in an icy grip.

For skiers who stick to groomed runs, avalanches pose little hazard. Most major ski resorts operate military-style control programs that rely on explosive charges to trigger slides on avalanche-prone slopes before skiers head for the lifts. But increasingly, skiers are stepping beyond the boundaries set by resorts -- prompted in part by long lift lines and the high cost of lift tickets as well as the thirst for adventure. "What they don't realize," says Dale Atkins, who forecasts avalanches for the state of Colorado, "is that once they cross under that quarter-inch rope, they've gone from a safe, managed area to the wild unknown of Mother Nature."

Backcountry skiers can substantially reduce their risk by heeding avalanche- center warnings, which rank the danger as low, medium, high and extreme. Forecasters routinely dig pits into targeted slopes to probe the condition of the snow below. Sometimes they even check the stability of the slope by carving ski-size slices through a test area, then standing or jumping on it. In general, south-facing slopes are less prone to avalanches because warmth from the sun promotes the bonding of the snowpack. Avalanches are also rare on slopes with inclines of less than 30 degrees. But there are exceptions to all these rules.

Though Coloradans were relieved that no lives were lost in last week's episode, many expressed resentment that the ski party had glided so recklessly into danger. At week's end Torp announced that he and his companions would raise money to defray the estimated $20,000 cost of a rescue effort that put dozens of others face-to-face with the white death.

With reporting by Joni H. Blackman/Denver