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TIME BOMB

18-Jun-2010
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At 13,642 feet, the Jungfrau is the tallest peak in a massif that includes the Eiger (13,025 feet) and the Mönch (13,474 feet). These craggy and windswept mountains, located in the Bernese Oberland region of the Swiss Alps, were once inaccessible, but the completion of the Jungfraubahn cog railway in 1912 simplified access to the Jungfrau massif, and the easy routes on the peaks became popular with climbers. This popularity, combined with the inherently volatile snow conditions throughout the Swiss Alps, has resulted in numerous fatal accidents. According to an Associated Press report, 32 people have been killed by snow slides in the Swiss Alps during July and August in the last 36 years.

At 10 a.m. on the morning of July 12, 2007, 12 Swiss soldiers from the Mountain Specialists Division accompanied by two guides were traversing a 45-degree slope on the southwest face of the Jungfrau when a slab avalanche, probably human triggered, swept two rope teams of three each 3,000 feet to their deaths. The eight remaining members of the party, including the two guides, were rescued unharmed. It was Switzerland’s worst military accident in 15 years. All healthy Swiss men are required to complete an average of 10 months of military service. The victims aged 19 to 23.

THE SOUTHWEST FLANK of the Jungfrau is the normal route and is considered an easy climb, but on the morning in question the mountain was blanketed by almost two feet of fresh snow and the avalanche risk was graded a three (on a scale of five) by the Swiss Federal Institute for Snow and Avalanche Research (SFI). According to avalanche-center.org, there are “at least three points along the route where avalanches come down regularly,” and the slide occurred on a slope that experts consider extremely dangerous. On the day before the accident, another group of climbers had triggered a slab avalanche on the adjacent Mönch and several guides sharing the Mönchsjoch hut with the army contingent warned the soldiers against trying the Jungfrau route. Soon after the tragedy, families of the victims demanded to know why the group went forward with the climb despite the warnings and clear indicators that the mountain was unsafe. In October the SFI opened an investigation into the accident. At the same time, the two guides were charged with “multiple homicides by negligence” as an examining magistrate from the Swiss military tribunal launched a separate investigation. Chris Huber, the investigating magistrate, has stressed that the guides are presumed innocent until proven guilty, but several prominent guides have been critical of the decision to attempt the peak given the hazardous conditions. The Swiss media has been particularly harsh in their censure of the army and the guides. The inquiry is ongoing.

Four variables determine avalanche danger: slope angle (terrain), snowpack, weather and you, the climber. In the case of the Jungfrau on July 12, all of the signs suggested that avalanche danger was high. The weather had been unstable and a slab avalanche had already occurred on a nearby peak, indicating that the new snow was not bonded to the layer below it. The guides and soldiers placed themselves at grave risk by entering dangerous terrain. Slab avalanches can run on any incline, but most frequently occur at an angle of 38 degrees, the steepest angle any granular substance (like sand) can achieve. This is called the angle of repose. Snow can hold on steeper slopes because the grains can bond, but as the angle of repose climbs above 38 degrees, the slope’s propensity to slide increases. Snow will rarely slide on slopes under 25 degrees. On slopes steeper than 55 degrees, snow sluffs off continuously rather than forming slabs. A snow-loaded slope of 45 degrees, however, like the one that slid on the Jungfrau, is a time bomb. 

There are many ways to assess avalanche danger including monitoring snow conditions—check out avalanche.org or csac.org, or digging a pit to check the layers—but the best way to stay alive when conditions are iffy is to stay home. As the authors of The ABCs of Avalanche Safety point out, “Nothing substitutes for formal instruction, routine practice, and plenty of experience.” Avalanche science is complex and beyond the scope of this article. See “Avalanche,” No. 141, for a more complete discussion, and a list of further reading and suggested courses.

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