Untitled Document

Avalanche mitigation efforts alleviate
potential hazards on U.S. 12

ITD and Lewiston Morning Tribune reports
U.S. 12 between Lowell and Powell was reopened Wednesday afternoon following successful avalanche mitigation efforts in the narrow Lochsa River corridor near Lolo Pass.

The only route between Lewiston and Missoula, Mont., closed Tuesday afternoon between mileposts 99 and 160 to allow ITD experts to assess the potential for avalanches and to try preemptive measures to control snow slides. The intent was to remove the threat of naturally occurring avalanches and reduce closure times that would have resulted.

Avalanche danger increased after rain began falling on more than two feet of new snow in the area. The addition of rain on the fresh snow caused a number of small slides to reach the roadway and cover both lanes. Other slides stopped before reaching the road, said Jon Barker, an ITD avalanche control expert.

"It looks like there were about eight places where little slides hit the road," Barker said. "Two of those went across both lanes up to 3 feet deep, some of them up to 6 feet deep on the near hill side."

Mark Schuster, a foreman at Lowell, said several trees weighted down with freezing rain fell across the road. He said closing the highway was the right call.

"I'm glad we closed the road," he said.

Barker said the avalanche chutes along the highway are now in much better shape because of the rain that fell in the area and melted much of the snow.

"This (weather) system did eat a lot of the snowpack out of the chutes and gullies. We are ahead in stability from where we were before this storm cycle started."

When temperatures cool to below freezing again, he said, the layers in the snowpack should bond.

"The more it cools, the stronger and stronger it is going to get."

He added some of the lower chutes still have a lot of snow in them and could become vulnerable to release as the snowpack builds.

The highway was also closed New Year's Day to early in the morning Jan. 3 when a number of small slides reached the road.

"One of them put snow four feet deep across both lanes and all the way to the bank toward the river. Another one stopped about 50 yards shy of the road. Another one stopped five yards short of the road."

An avalanche in the same area last year blocked U.S. 12 and extended into the Lochsa River, temporarily stranding about a dozen semi trucks and trailers. Removal of the debris and concern over continuing avalanches prompted closure of the important commercial route for more than two weeks early in 2008.