Bombs away - avalanche research in the Bridgers

by Evelyn Boswell

February 21, 1996 BOZEMAN - Jim Dent and Ed Adams would sure like to set off some more bombs in the Bridger Mountains over the next few weeks.

With two or three people stationed in a shed behind a rock, Dent and Adams want to see what happens when a two-pound bomb triggers an avalanche just north of Bridger Bowl near Bozeman. The shed sets in the path of the avalanche.

"There's a great big window. You can see the avalanche go by," said Dent, associate professor of engineering mechanics at Montana State University-Bozeman.

Dent and Adams are part of group at MSU that's been studying avalanches for about 20 years. The group has looked at everything from avalanche initiation and stability to avalanche velocities and impact pressures. Avalanche velocities is the current focus of their experiments.

"We will have as many more experiments (this season) as we get storms that dump enough snow," Dent explained. "We will typically go through the end of March."

"We've got plenty of winter yet," Adams predicted in mid-February.

A helicopter flies most of the group's equipment to the site in the fall. From then on, the researchers have to ski in their supplies on their backs. They ride to the top of the Bridger ski lift, take a rope tow to the ridge, hike along the ridge until they're out of the ski area, and drop down to their avalanche study area.

Depending on the weather, the researchers then set off a two-pound cast primer bomb, Dent said. They set off one bomb per avalanche and normally trigger five or six avalanches from January through March.

People running the instruments get run over by the avalanche, but they're protected by a wooden-frame shed bolted onto the downhill side of a rock, Dent said. The rock is the size of a small car, and no one has ever gotten hurt.

"The slope we are working on is fairly small so we can control things," Dent continued. "Our avalanche is only about two feet deep. The avalanche path ... is about 10 yards wide and maybe 200 yards long."

The group has made several discoveries so far, but the main one lately is that "the avalanche pretty much slides as a whole instead of flowing like water," Dent said. "It's more like a block sliding than like a liquid."

That discovery might not affect the average skiier or snowmobiler, but it helps researchers predict various aspects of an avalanche, Dent said.

Please send your name and city/state/country to Evelyn Boswell and Carol Flaherty, MSU Communications Services, Bozeman, MT 59717. If your browser (NetScape) supports the "MAILTO" tag then email us at carolf@montana.edu.

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