Unusual Snowpack Means Unusual Avalanches

Jan 21, 2016

A recent avalanche on Donner Peak.
Credit Sierra Avalanche Center

Unusual snowpack conditions in the Sierra Nevada mountains are contributing to an increase of a type of avalanche quite uncommon for the area. Our contributor Luiza Vieira has the story.

Even with all the snow Northern Nevada and California are receiving, the number of avalanches has not increased. The Sierra Avalanche Center, however, is seeing a type of avalanche that has not happened in this area in years.

It’s caused by what’s called surface hoar, a type of frost. Once that frost is buried in the snowpack, it forms a persistent thin layer that can break easily and move the snowpack down the mountain, causing an avalanche.

“It’s like dew in the winter time," says Andy Anderson, a forecaster for the Sierra Avalanche Center. "You know, in the summer when you wake up in the morning and everything is moist and dew? In the winter, the same thing happens except that dew freezes and forms very feathery, fragile snow crystals on the surface. If you bury that layer in the snowpack, it forms a very weak layer.”

Anderson says the problem with buried frost is that it can cause avalanches to happen on different types of terrain, including slopes that are less steep.

“It doesn’t look like it is as big and intimidating as the upper elevation terrain is, but it is," he says. "It is just a little bit sneakier.”

Anderson says most avalanche accidents are actually triggered by the people involved and could be avoided if they had the right knowledge and tools before going out into the backcountry.