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Idaho 21 closed only 30 days by avalanches in '07-08

Avalanche-related closures on Idaho 21 were significantly reduced this winter by using explosives to bring down unstable snow before it could slide and block the highway.

The avalanche season officially ended last weekend.

Idaho 21, one of Idaho's popular winter recreation routes and host to the most of the state's avalanches, is typically closed 60 days per year, but was closed just 30 days this winter through these pre-emptive measures.

"This is a great accomplishment given the heavy winter we had," said ITD lead avalanche forecaster Jon Barker. "We had 53 avalanches slide onto the roadway - the second highest number of slides ever recorded in one winter."

According to Barker, the largest avalanche to slide onto the highway this winter measured more than 16 feet in height.

Three different methods were used in this first-year program to deliver explosives:

An avalauncher (a cannon-type device) to deliver explosives into avalanche chutes
"Heliblasting" to drop explosives in avalanche-prone areas by helicopter
When conditions warrant, ITD avalache mitigation crews ski into areas and set charges by hand

Those procedures bring down the snow accumulating in the chutes, reducing avalanche hazards and allowing ITD crews to safely clear snow from the roadway.

ITD received a special-use permit from the U.S. Forest Service to use these measures to reduce the avalanche hazard on Idaho 21 between Grandjean Junction and Banner Summit. The 11-mile Canyon Creek section, part of the Boise National Forest, has 64 avalanche chutes and experiences about 90 percent of the state's avalanches affecting roadways.

The agencies worked together closely to ensure natural resources in the region are protected in the development of a long-term avalanche control program.

The department also uses other tools to manage avalanche danger. Information is gathered using technology such as weather stations and snow-density testing to determine when avalanches are likely. ITD recently installed an additional weather station to provide the best possible weather-related information for avalanche forecasters.

"Our primary goal is to ensure safety," said ITD Regional Engineer Tom Points. "The expanded program also provides more reliable access to winter recreation areas along this highway and to the community of Stanley."