Scientists Risk Their Lives to Study Avalanches

If a scientist stands in the way of 150 tons of snow crashing down a mountain at 50 mph, can he figure out why it let loose and when it will again?

Wednesday, December 01, 1999
The eastern face of the mountain is avalanche terrain. There are no trees to anchor the snow. A screaming wind picks up even more snow from the mountain's far side and deposits it onto a bulging cornice that threatens to crack under its growing weight. The slope here is steep, 40 degrees, and the snowpack must cling like a prostrate man on an A-frame roof. Inevitably it loses its grip. To ski this slope after a heavy snowstorm, you would have to be either exceptionally unwise or an avalanche researcher. Four of the latter—Bob Brown, Ed Adams, Jim Dent and Karl Birkeland, of Montana State University—are making plans to do just that. Their destination is a plywood shack in the protective embrace of a small rock outcropping—directly in the path of an avalanche. The structure is nine by six feet, enough room, barely, for two scientists (the rest retreat to the edge of the slide path), an array of instrumentation, a gas-powered generator, and one rather nervous journalist. 

When all is ready, one of the men will ski to the top of the ridge, hoist four pounds of explosives on a pulley out over the crown of the slope, and light the fuse, sending vast amounts of snow down on his colleagues’ heads. If you want to understand the dynamics of avalanches, these men reason, what better place than smack dab in the middle of one?

In the weeks leading up to this event, I have been in the Swiss Alps, because the best way to learn about avalanches is to pay a visit to the very impressive, very modern Swiss Federal Institute for Snow and Avalanche Research (SLF), located in a small ski resort town called Davos. Switzerland spends $2.5 million a year on avalanche research. The architect who designed the raised-marble snow crystal motif on the lobby floor probably got paid more than Bob Brown’s entire budget for 1999. But the Swiss have a compelling reason to spend this kind of money on understanding avalanches: More than 50 percent of them live in avalanche terrain. In the 1998-1999 season, hundreds of major avalanches hit the Swiss Alps, causing more than $100 million in damages and killing 36 people. It was the most destructive season in more than 45 years.  

Like Bob Brown and his Montana team, the Swiss also have a mountain avalanche hut. At the moment, it’s out of commission. Last week an avalanche of unanticipated ferocity let loose and destroyed millions of dollars’ worth of test equipment. Just hours before, two men had been in the avalanche’s path installing radar equipment that clocks the speed of tumbling snow. Had fate been running on a slightly different timetable, they would be dead. Immediately after the avalanche, a group of researchers who had watched the destruction debated whether they should venture out and salvage what remained of the equipment. “We thought: Okay, it’ll be very rare that two avalanches hit within five minutes,” recalls physicist Dieter Issler, SLF’s reigning expert on avalanche dynamics. While they deliberated, a second avalanche let go. Avalanche research is a lot like lion taming. Most of the time, it’s safe, but when it’s not, it’s very, very not.

Why do researchers risk their lives like this? In part, because few other jobs require one to ski through some of the planet’s most reliably gorgeous scenery. And although there is an inescapable sense that the danger itself is appealing, they do it to save lives. The more that is known about the dynamics of avalanches, the easier it becomes to accurately predict where, and how far, they’ll tumble down any given slope into any given valley. Flow models are employed to make zoned maps that Swiss planners use to keep people from building homes in the runout path of potentially catastrophic avalanches. If researchers know the steepness of the mountain slope, along with various friction parameters, they can calculate how far an avalanche is likely to flow given any number of different slab depth scenarios—a slab being the layers of snowpack that break off and slide down the mountain. One former director of the SLF lives in what is now a blue zone—the second-highest risk zone. In 1968, an avalanche of humbling dimensions stopped, literally, at his door. “Actually, it came in under his door,” Issler says. “Then it stopped.”

Issler stands beside a 10-foot-long Lucite tube containing water and dandruff-sized polystyrene particles. It’s essentially a big, long, banana-shaped snow dome. When Issler presses a button, a sliding door will retreat, sending the particles plunging down the slope, roiling and billowing into a tabletop-scale avalanche.

Issler presses the button, then peers up into the top of the tube. “Hmm,” he mutters. He thumps the Lucite with the heel of his hand. “The person who was in charge of cleaning it has retired,” he says. Finally, his captive avalanche plunges to life. “See, there’s the powder cloud.” A major avalanche—one that runs for 1,000 feet or more—will develop a towering cloud of agitated, airborne snow crystals that rides along above the tumbling snow.

No puff of air in your face, this cloud. This one kills. It snaps conifers like matchsticks and turns vacation chalets into kindling. While the snow portion or “dense flow” of an avalanche will typically stop when it hits an uphill grade, a powder cloud often rushes on, ushering mayhem up and over the top of the hill. The largest powder cloud Issler ever studied was a quarter of a mile high; its 100,000-ton mass traveled three miles before halting.

But it doesn’t take a big avalanche to kill people—the vast majority of deaths occur in slides that run no farther than 200 yards. Avalanche debris is nothing like the airy, fresh-fallen snow of skiers’ dreams. The snow crystals in the debris pile left by an avalanche are packed together so densely that they feel more like concrete than snow. The snow that buries the typical victim is only 50 percent air, as opposed to fresh snow, which is 80 percent air. You cannot move—or even expand your chest to breathe—let alone dig your way free. Suffocation is the means to the end in two-thirds of avalanche deaths. The remaining third die from the trauma of being flung against boulders and trees at speeds of up to 80 mph. Some victims are done in by their own breath, which condenses and then freezes on their faces, forming an ice mask that slowly cuts off what little air remains. Only one avalanche burial victim in four lives to remember it.

Clearly, the best thing to do in an avalanche is to stay up near the surface. How to do that was, until recently, not clear. For years, people were told to wriggle out of their backpacks and try to “swim” to the surface. But recent research suggests that you are better off keeping the pack on and covering your face with your hands to create a breathing space. This is because the larger you are, the more likely you are to end up at the top of the avalanche debris. Why? For the same reasons that the biggest potato chips are always at the top of the bag. Through a process known as “squeeze expulsion,” particles big (you and your pack) and small (rocks, chunks of snow) knock into each other at the bottom of the avalanche, where the most impacts occur, and eventually get bumped up to the top. Simultaneously, due to a process called “random sieving,” the small chunks drop back down through the voids between particles. The rest—too large to fit through those spaces—remain near the top.

Even without a pack on, a person caught in an avalanche is usually a large enough entity to remain within a couple of feet of the surface. People who end up six to 10 feet under are usually caught in slides that drop down into a gully or get stopped abruptly by an obstacle, allowing the snow behind them to pile up on top of them. To quote Schweizer: “They’re done for.” But plenty of people have suffocated under less than two feet of tightly packed avalanche debris. Fifty-nine percent of victims buried in 2 to 2.9 feet of snow perish.

Car four of the davos cable car holds the regular assortment of brightly hued skiers and teenage snowboarders. But one man carries no skis. It’s Martin Schneebeli, the resident snowpack structures expert, commuting to the SLF’s field research area, a series of cold labs at the top of a mountain directly above the town.

Three-quarters of the way up the mountain, Schneebeli, my guide for the day, points out a patch of snow checkered with deep square pits. These snow pits, as they are called, are the basic tools of avalanche prediction. The layers visible on the walls of the pits reveal the history of the past few months’ snowfalls. To determine the avalanche risk, forecasters visually assess these layers to ascertain the stability of the resulting snowpack.

The snow piling up outside right now is wild snow—light, dry, freshly fallen—the very stuff of dangerous avalanches. If the wind picks up, the risk will ease: High winds will pack a pile of snow crystals together tightly, making the snowpack sturdier.

In the world of avalanche prediction, weather calls the shots. Spring thaws can weaken the bonds that form between crystals as the snow melts and refreezes, paving the way for deadly, heavy, wet snow avalanches. A strong sun will melt surface snow, which then refreezes at night into an icy crust, off of which the next layer of snow can easily slip. A similar slippery and fragile snow layer is something called “surface hoar”— essentially a morning frost on top of the snow that gets buried by more snow.

Sharing top billing in the rogues’ gallery of weak layers is a wily meteorological entity known as “depth hoar.” In early winter, when the ground is still warm, heated and moistened air rises through the snow and cools into a layer of spiky, recalcitrant, depth-hoar crystals—pretty to look at, but weak as kittens. In a 32-degree Fahrenheit room in the Institute’s field station, researchers Charles Fierz and Thorsten Baunach create depth hoar in a box to determine how quickly it grows under various snow and weather conditions.

Schneebeli looks at my Timberlands. I assure him they’re warm. “They are not warm,” he tells me in the same deadpan monotone in which he claims that Schneebeli means “snowman” in Old German. He leads me to a cabinet full of voluminous goose-down snow pants and bulbous rubber “moon” boots that appear to be sized for Clydesdales.

Now I am warm. In the corner of the cold lab are 12 cardboard Chiquita banana boxes filled with snow. Fierz scoops some of it into a sieve and hands it to Baunach. “Now we make a snowfall!” Baunach says, grinning like a kid. He shakes the sieve over a box to re-create inside the lab what has been happening outside for the past 12 hours. Like a hypercritical head chef, Fierz points to lumps in the mound of sifted white: “Try double sifting,” he suggests.

Fierz and Baunach will take snow samples from their boxes every 12 hours, as the snow’s temperature rises from minus four to 30 degrees Fahrenheit. The snow is shallow—only about two-and-a-half inches. The shallower the snow, the steeper the temperature gradient between the ground-warmed bottom (being played, in this case, by a heated metal plate) and the air-chilled top of the snow. The warm air rises, cools quickly, and becomes frost crystals. Fierz’s experience as a skier tells him in general what his experiment will tell him in detail. “A few centimeters of new snow, followed by two or three days of nice, clear, cold weather,” he intones. “You’ll get depth hoar.”

Fierz is wearing red ski boots. At the end of the day he will ski home—through very risky avalanche conditions. The uphill-bound cable-car service ended for the day shortly after my  morning ascent. (A slide destroyed the tracks in 1968.) It wouldn’t be Fierz’s first avalanche. Like many of the avalanche researchers I spoke with, he himself has been caught—not while on the job, but while backcountry skiing. “I was not really scared,” he shrugs. “Luckily, I could always see where I was going.”

Bob Brown was scared. The Montana avalanche researcher was on a backcountry ski trip seven years ago when a companion triggered an avalanche directly uphill from him. He tried to hide in a hole in a snowdrift. “I thought it would go right over me. It blew me up out of that hole like a rag doll. Carried me 150 yards downhill. I must have gone from zero to 60 in about a second.” Brown saw a tree coming up and tried to grab hold, but the avalanche ripped it from his grasp. Grabbing the tree did help pull him to the top of the slide, however, so he wasn’t buried deeply and suffered only minor injuries.

I’d rather not hear this story just now. Fifty yards above me, an avalanche of undetermined size is about to be set off. The only thing between me and a surging wave of killer snow is a three-walled plywood shack. Brown sips hot chocolate inside the shack while his colleague Jim Dent sets up data readers. “I don’t like to say ‘shack’,” says Brown. “I like to say ‘chalet’.” I point to a pair of crossed support beams, their intersection lashed together with duct tape. Brown shrugs. “We haven’t had any trouble so far.” Dent wipes his nose. “Except the year the roof caved in.”

Outside the shack, Ed Adams and Karl Birkeland are busy with portable shovels, clearing space in the snow to lay down equipment that will log the snow’s temperature as the avalanche passes. They hope to disprove a stubborn and thus far unfounded assumption about avalanches: that the friction at the bottom of the slide is vigorous enough to heat the snow to the melting point. As the assumption goes, the melted snow then quickly refreezes, pinning the trapped victim like a Popsicle stick.

I ask Adams what would happen if the avalanche let go on its own while we were out here. “See those flats?” Adams points down the slope. “You’ll end up down there.” Brown sticks his head out of the shack. “But first, you’ll have to go through those trees. That’ll beat you up real bad.”

I mention that it hasn’t snowed that much, and that the avalanche risk is low to moderate today. Adams points out that the snow being deposited on the ridge top by a strong wind is a significant factor that shouldn’t be overlooked. It was Jim Dent’s research that revealed one of the mechanisms by which windblown snow accumulates at the top of a ridge. He discovered that when snow gets blown around, it picks up an electric charge. As windblown crystals hit the snowpack, particles with opposite charges are attracted to each other and stick together to form a cornice.

I ask Jim Dent what it’s like in the shack during an avalanche. “It just gets grayer,” he says. “I like to stick my hand out into the avalanche as it goes by. It’s like putting your hand into a river.” He tells me that if I want a good view, I should climb up onto a platform nailed to a tree 100 yards downhill and 30 feet to the side of the slide path. So I do. From my perch, I watch Adams ski up to the top, his backpack bulky with explosives. Then two other researchers ski off to the side, much farther to the side than my tree. The path from Adam to me looks like a straight line. Apparently, the avalanche turns as it flows downhill. I try not to think about it. I listen to the “wooo-hoos” of skiers on the neighboring slope and admire the big Montana sky. If these are to be my last sights on this earth, I couldn’t have picked a nicer view.

Five, four, three, two . . . A tumble of choppy white emerges from beneath the bomb’s sooty smoke cloud: Avalanche! Having only seen the slow-motion, zoom-lens rendition of an avalanche, I’m shocked at how fast it is. I’m reminded of a documentary I saw about the Hoover Dam, which showed water raging back into the riverbed for the first time. By the time the slide passes me, it has spread and flattened itself out, becoming a rippling disturbance in the snow. It’s as though something had gotten under the mountain’s skin. There’s an eerie, almost hallucinogenic quality to the sight: Fallen snow, something I’ve always thought of as stationary and benign, suddenly come to life.

Back up at the shack, Adams sits in the rubble, holding a thermometer in the snow like a concerned mother. Brown is shaking his head. He had hoped a 15-inch layer would break loose from the snowpack and slide. It was considerably smaller. “The snow set up too much,” he says. “It was too warm.” He sounds like a chef assessing a failed soufflé. But Brown has high hopes for another big slide before the season ends. It’s late February now, so he figures he’s got one more shot at it. Or it’s got one more shot at him.

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