Crews in Idaho are working to reopen State Highway 21 in Central Idaho after a massive avalanche buried it over the weekend.
BOISE, Idaho – A large avalanche has closed a section of a central Idaho highway, and officials say the road will remain closed “until further notice” until the massive amounts of snow are removed and conditions are determined to be safe for drivers.
Officials with the Idaho Transportation Department (ITD) said State Highway 21 between Grandjean and the Banner Summit was closed on Sunday when the massive avalanche slid down a mountain and buried the road.
This image shows the massive avalanche that closed State Highway 21 in Idaho.
(Idaho Transportation Department/Facebook / FOX Weather)
The closure currently impacts the highway from Milepost 93.7 to 105.5 and will remain closed until further notice.
“We do not close highways without reason, and this slide is a perfect example,” the ITD said in a Facebook post.
According to the department, the biggest section appeared to be about 40 feet deep.
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This image shows the massive avalanche that closed State Highway 21 in Idaho.
(Idaho Transportation Department/Facebook / FOX Weather)
The department shared dramatic images of the avalanche and showed snow covering the highway, as well as crews working to remove it from the road.
The ITD said crews were hopeful that the road could be reopened by Monday afternoon or Tuesday. However, according to Idaho 511, conditions would be reassessed on Tuesday morning.
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Deadly avalanches have been reported across some western U.S. states recently.
Officials said an avalanche killed a skier and injured another at Utah‘s Big Cottonwood Canyon over the weekend. Also in Utah, a Wyoming man was killed in an avalanche while he was snowmobiling with a friend earlier this month.
In this episode of the FOX Weather Ski House, FOX Weather Meteorologist Bob Van Dillen joins a Steamboat Ski Resort crew as they conduct avalanche mitigation at the summit of Mount Warner in Steamboat, Colorado. FOX Weather Ski House is sponsored by Eddie Bauer. (Video from January 2025)
An avalanche is a rapid flow of snow down a mountain, hill or any steep incline and can be triggered from below or from a distance.
Avalanches can happen any time there is snow, but the risk is increased at certain times of the year.
They often occur when fresh new snow falls on top of an already-compacted snow base. That newer snow becomes unstable, triggering an avalanche.
A dramatic video shows a snowboarder triggering and then outpacing an avalanche on New Hampshire’s Mount Washington last month. The video shows the moment a layer of snow started to slide down the mountain behind the snowboarder going down Tuckerman Ravine. (Video from December 2024)
Heavy snow and strong winds can also result in natural avalanches, but the National Weather Service says that manmade avalanches are much more common.
“In 90 percent of avalanche incidents, the snow slides are triggered by the victim or someone in the victim’s party,” the NWS says. “Avalanches kill more than 150 people worldwide each year.”