Forecasters in Colorado are warning of “very destructive” avalanches as heavy snowfall and strong winds are expected Wednesday.
Avalanches have already buried cars, killed skiers and left chunks of forest scattered across highways — even dangling from power lines — in what’s considered a historic avalanche season. But Colorado isn’t alone.
“We've had a number of large storms coming across and hitting California and then hitting Utah, Wyoming, Idaho, Montana and with some of these large storms we've had very large avalanches as well,” says Karl Birkeland, who directs the National Avalanche Center with the U.S. Forest Service. “It's just that the events in Colorado have been historic.”
He says Colorado hasn’t seen avalanches this big in 50, maybe 100, years.
“They've been landscape-changing events in some cases where they've been knocking out acres and acres and acres of trees and forests,” says Birkeland.
He says it isn’t as simple as the amount of snowfall, it also has to do with the timing -- in this case, early snow in October followed by a dry November, which formed a weak layer in the snow.
“And then just in March we've gotten this very, very large storm and that large storm was enough to finally overload the snowpack and create these conditions that resulted in all these large avalanches,” he says.
When it comes to hurricanes and floods, the refrain is that climate change will mean more extreme events in the future.
“I would say that we don't know if that applies. And I think it's going to change from one location to another,” says Ethan Gutman, a hydrologist with the National Center for Atmospheric Research.
Scientists studying studying climate change in western ski areas have predicted that in 2100, wet avalanches could start between 16 and 45 days earlier than usual based on greenhouse gas emissions in coming years.
“This year has really been a big year just because of the volume of snow we've had and it starts to make one wonder whether climate change plays a role in this or whether this is just within the realm of natural variability,” says Gutman. “There is a possibility that increasing temperatures means there will be less snow at some times, which would decrease the risk of avalanches. But increased temperatures can also increase the amount of water in the air so that when you do get snow, you might get more snow, and that could actually increase the risk of avalanches.”
Erich Peitzsch, a physical scientist with the USGS Northern Rocky Mountain Science Center, says part of the difficulty in disentangling how climate change could affect avalanches has to do with the lack of historical data.
“Most of the records come from historical observations,” he says, like reports from railway workers and highway workers. “It's a limited historical data set.”
Peitzsch is trying to fill gap that, at least for four mountain ranges in northern Montana, by looking at tree rings.
By slamming into trees, avalanches can leave scars or sometimes actually squish a tree ring so that it’s thinner on the side that got slammed and thicker than on the downhill side. Peitzsch says he’s found such scars going as far back as the mid-1600s.
“At least here in the northwest part of Montana, we found that there seems to be some relationship with the El Nino southern oscillation as well as the interaction with what we call the Pacific Decadal Oscillation,” says Peitzsch, who is still analyzing his results.
The Colorado Avalanche Information Center says, “Quickly changing conditions will make human-triggered avalanches likely.”
As a post on the center’s Facebook page recently warned, “This is not the time to try and outsmart Mother Nature.”
This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Boise State Public Radio in Idaho, KUER in Salt Lake City and KRCC and KUNC in Colorado.