Snow Science Against the Avalanche

One morning, Pierre Huguenin, a forty-nine-year-old mountaineer and snow scientist, drove me to the site in a white Mitsubishi Pajero. “You see the flakes. You see the crystals,” he said, gesturing out the window. There had been a storm the previous night. He stopped the car where the road ended, and we changed into snowshoes.

Outside, there was about a foot of pristine powder. I stooped and ran my hand through it. Bone-dry, it was the pure bright white of confectioner’s sugar, with the texture of sea salt. Huguenin pulled out his phone. The avalanche forecast for the area had us covered in orange. “We are in the third degree,” he said—the risk category in which the most avalanche deaths occur in the Alps, equivalent to the American “considerable.” He pulled out two avalanche beacons—transmitters that would relay our location to rescuers—and set them to Send. We strapped them under our jackets.

“My job before working at the S.L.F. was at a salmon plant,” Huguenin said, as we set out. (He was an engineer there.) “It was so loud.” Now we could hear the river as we walked. Beneath the blue sky, ours were the only tracks. After twenty minutes, the site came into view: a broad, bare mountainside, eight thousand feet high. Between two couloirs—the main avalanche paths—a half-dozen chalets huddled near a small wood.

“They are not allowed to live here in the winter,” Huguenin said. Two days earlier, there had been a naturally occurring glide avalanche at the site. I asked whether it had been dangerous. “You would be dead,” he said. “No chance.”

The site was built in 1997; in the winter of 1999, the snow was the heaviest it had been since 1951—perfect conditions for an experiment. Using explosives dropped from a helicopter, the S.L.F. triggered three avalanches in the course of a month. They were so massive that they destroyed most of the institute’s equipment. If you had been skiing on the mountain during the last avalanche, you might have heard a soft exhalation: air releasing from a crack in the slab. Upslope, it would have looked as though someone had slit the mountain’s forehead. Now its face was falling off; the break, nine football fields across, was as deep as eleven feet in places. Blocks of snow would begin leaping up prettily, breaking like roiling water. In the quiet, you might feel something lapping at the back of your legs before being swept off your feet.

The slide generated a powder cloud nearly two hundred feet high. It seemed to move in slow motion, like dry ice billowing, but it levelled the trees. Underneath, the core was formed by four hundred thousand tons of snow. Huguenin asked me to visualize the test peak, two kilometres distant, and the peak of the mountain on which we stood as the two sides of a half-pipe. With a deep roar, he said, the avalanche had run through the valley like a skateboarder, with enough speed to climb the other side.

“It came all the way up there?” I asked, pointing to the top of our peak, three hours’ hike away.

“Yup, and there is a trail there. One of the wards was on it. The guy at that time saw a huge amount of snow jumping the top here”—he motioned toward the ridgeline above us—“and falling on the other side.” As the snow poured over the ridge, the warden could hear tree trunks snapping like matchsticks. “He really thought he was going to die,” Huguenin said. The experiment, which destroyed much of the forest, didn’t go over well with the locals.

Huguenin and I continued walking. To our left, a Soviet-looking bunker poked out of the hill. It was two stories tall; in the 1999 experiment, it had been covered by thirteen feet of snow. To reach the observers buried inside, a crew had to cut a vertical tunnel with a chainsaw. Near the bunker, an array of continuous-wave radar antennas, designed to measure the flow at the avalanche’s core, craned toward the peak. Huguenin pointed to “obstacles” on the slope—pressure and velocity sensors mounted on concrete-and-steel structures. Against the mountainside, the largest obstacle, a sixty-foot-tall pylon studded with flow-measurement devices, looked like a toothpick.

Avalanche country is like bear country. The threat hardly ever comes, but it defines the place, and lends it its grandeur. Outside the bunker, the mountains rose around us; flat clouds gathered in a distant valley like steam. We had lunch: bread, cheese, chocolate. The snow was warming in the sun. Scooping it up, I found that, instead of seeping through my fingers, it now formed a perfect snowball—metamorphism within a matter of hours. I thought of how plants observed in time lapse seem to move with animal purpose. I imagined the crystals in this newly fallen snow sintering and crackling with life.

From where we were sitting, we could see the glide avalanche from two days earlier. It was hard to get a sense of scale. Huguenin handed me his binoculars. Through them, I saw chest-high boulders of snow. Without them, the avalanche was a scratch on the mountainside.

One is unlikely to encounter an avalanche on the bomb-cleared trails of a ski resort like Alta. Avalanche accidents happen far more often in the backcountry, where skiers search for what the First Nations author Richard Wagamese called “the great white sanctity of winter.” In a recent survey, more than half of backcountry skiers said they had triggered an avalanche; a quarter said they’d got caught in one. It’s telling that the standard kit separating them from resort vacationers consists of a beacon, a probe, and a shovel.

I grew up skiing at small mountains in the Laurentians, just north of Montreal. Well groomed and popular, they were often scraped to ice. It was only a few years ago that I went with a friend to a large ski resort in Colorado. One day, we travelled to a remote part of the mountain. There had been fresh snow that morning, and I whooped as I dropped in, not another soul in sight. The snow felt like a cloud underfoot; falling evoked the childhood joy of jumping in leaves. Carving slow curves, I recognized the feeling of discovery: I was writing my name on the mountain. I also understood, for the first time, how powder and silence lure skiers into the backcountry.

To some extent, backcountry skiers can rely on avalanche forecasts. At the Utah Avalanche Center (motto: “Keeping You on Top”), forecasters make daily field observations (“+” means fresh snow; “.” round grains; “Ʌ,” depth hoar), integrating them into uncannily specific recommendations: “It remains possible to trigger a wind slab avalanche. . . . This snow will feel upside down and stiff.” Different kinds of terrain are assigned levels of danger, on a one-to-five scale; colorful diagrams with cartoon icons show which parts of the mountain—above the treeline, say, or southern aspects—are to be avoided.

Some experts worry that such diagrams give skiers a false sense of security. My sixty-seven-year-old godfather, Richard, happens to be the most experienced backcountry adventurer I know; a snowboarder for decades, he has logged more than a hundred thousand vertical metres in the past two years, in Kashmir, Antarctica, and other places. In the backcountry, he relies not just on forecasts but also on guides, to whom he attributes extraordinary diagnostic powers. Before taking a group out, a guide might dig a small column out of the slope. He’ll examine the layers, sussing out weakness, assessing the look of the crystal grains. Then he’ll tap the top of the column with his hand ten times, bending from the wrist. If the column survives, he’ll do it again, bending from the elbow; finally, he’ll do it from the shoulder. His interest is in when the column collapses, and how. Once, on a slope that seemed risky, a guide told Richard’s group that, whatever they did, they must follow, one by one, to the right of his line. Each skier followed in turn, carefully staying to his right. As Richard descended, a layer of snow unsettled beneath him, a few feet to the left of the guide’s tracks, and sent a wave across the bowl. The slope fell like a sheet.

“Big mixup at the airport. I’ll tell you about it later. I see my bag waiting for me.”
Cartoon by Pia Guerra and Ian Boothby

One way to avoid avalanches is to ski shallower slopes. Slopes of around twenty-five degrees are perfectly enjoyable; steeper ones are only marginally more fun. And yet it’s hard for skiers to hold back. “The tricky part is controlling our lust,” a forecast reads. After a student of his died in an avalanche, Jordy Hendrikx, a professor at Montana State University, shifted his focus from geophysical research to behavioral science. (“Understanding how a crystal grows is not enough to change the current fatality profile,” he told me.) In one long-running study, he had a large group of backcountry skiers log their activity with a G.P.S.-enabled app. He found that experts chose steeper terrain, as did all-male groups, especially younger ones. (“Quantifying the obvious,” he has said.) When Tremper published his book, in 2008, he reported that, although a third of those who used the backcountry in Utah were women, women accounted for only 3.3 per cent of fatal accidents.

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