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Issue
11.03 - March 2003
Avalanche!
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.
By Marc Spiegler
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 198 1, 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.
Corbis
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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 Evolène, 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.
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