Avalanche

An avalanche crashes through a rocky ravine on Mt. Everest

Avalanche frequency is on the rise in recent years.

Avalanches kill approximately 150 people worldwide every year, and 90 percent of these avalanches are triggered by humans. Most avalanches occur within 24 hours after a storm unleashes 12 inches or more of fresh snow. Avalanches happen when four factors intersect: a steep slope, fresh snow cover, a weak layer in the underlying snow layers, and a trigger.

Chart showing the number of deaths by avalanche from 1951 to 2016

This chart shows the number of avalanche deaths per year from 1951 through 2016. The increase in numbers in recent years reflects the growing number of outdoor recreationists venturing into the backcountry.

The majority of avalanches occur on slopes that are between 30 and 45 degrees. Slopes steeper than 40 degrees tend to shed (or slough) snow before it gets a chance to build up, and slopes that are less than 30 degrees rarely have the gravitational force to move. 

Avalanche fatalities by state from 1951 through 2016

The state with the most avalanche fatalities between 1951 and 2016 is Colorado, followed by Alaska and Washington.

Don't become a statistic: Unless you have professional avalanche training, don't venture into the backcountry in winter.  Learn how to get trained and where here.