Avalanche mitigation program reduces number of winter closures on Idaho 21

Avalanche-related closures on Idaho 21 have been significantly reduced this winter through the use of explosives that bring down unstable snow before it slides and blocks the highway.

The highway, one of Idaho's popular winter recreation routes and host to the vast majority of the state's avalanches, is typically closed 60 days per year. But this winter – one of he hardest in recent years – Idaho 21 has been closed just 28 days, largely because of ITD’s preemptive measures.

"Given the heavy winter we have had this season, this is a positive sign that we will be able to reach our goal of reducing closure days by about half," said ITD lead avalanche forecaster Jon Barker.

Three primary methods have been used in this first-year program to deliver explosives:

1. An avalauncher (similar to a cannon) that delivers explosives into avalanche chutes
2. "Heliblasting" a process of dropping explosives from helicopters into avalanche-prone areas
3. When conditions warrant, ITD avalanche mitigation crews ski into areas and set charges by hand

Those triggers bring down the snow that has accumulated in the chutes, reducing avalanche hazards and allowing ITD crews to safely clear snow from the roadway. Bringing down snow accumulations enables crews to clear highways faster and more efficiently than if avalanches are left to occur naturally.