Monday, March 18, 2024
Gigantic avalanches breaking in southwest Montana
Unusually large avalanches have been raking the backcountry of southwestern Montana, the biggest one on Henderson Mountain near Cooke City stretching 2,000 feet wide and breaking 10 feet deep.
Big avalanches
“That is a HUGE slide, especially for one that was human triggered,” wrote Ian Hoyer, of the Gallatin National Forest Avalanche Center, in his March 8 forecast. “Thankfully, remarkably, the rider wasn’t caught,” although the snowmobiler was partially buried.
Amazingly, no one has been killed this winter by a slide in the region despite the hair-trigger snowpack, but that hasn’t stopped avalanche forecasters from worrying.
“The magnitude of the slides makes my stomach turn,” wrote avalanche forecaster Dave Zinn on Tuesday.
“Things really fell apart about 10 days ago,” said the center’s Alex Marienthal.
That’s when heavy snowfall — about 9 to 10 feet in some places — stacked up. Strong winds helped create large cornices that were also stressed by the additional snow weight. Even more unusual, slides began occurring on lower angled slopes where people had been able to safely travel in the past and some slides were being triggered from far away.
“Cooke City is a place that almost every year impresses us, or surprises us a little,” Marienthal said. “A place with that many big mountains and avalanche terrain and people, there’s just a lot going on there.”
The weak layer of snow dates back to December and early January, Marienthal said. Dry, cold snow and weather meant the snow didn’t adhere to the surface, even when milder weather swept through the valleys.
“We always have weak snow to some extent,” Marienthal said. “We always see some activity here and there, but to have it on almost every mountain … and going out so wide is because the weak layer has stayed so intact and continuous.”
In his March 11 report, Marienthal wrote is was “possibly the most widespread large avalanche cycle” he has ever seen with avalanche danger across a large area rated “considerable.”
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