Avalanches are masses of snow sliding down slopes. There are several types, but the most dangerous are slab avalanches. Slab avalanches can form when stronger snow overlies weaker snow. The difference in strength can be very subtle or quite dramatic. Often, human triggered slab avalanches are 1-2 feet deep, have an area about half the size of a football field, and can reach speed over 20 mph within seconds.
The other problematic avalanche type in Colorado is a loose snow avalanche. Loose snow avalanches are a greater issue in spring, when the snowpack surface is rapidly warming and losing strength. Loose snow avalanches happen when the surface snow has little strength. They usually start from a point, often under trees or cliffs. A chunk of snow starts tumbling, and knocks more snow loose. The loose avalanches fan out as they descend. Loose avalanches can be big enough to tumble a rider or climber around, and can have serious consequences if they carry you into trees, confined gullies, or over cliffs.
There are many resources to learn more about avalanches. Some of the best information on avalanches and avalanche safety are in these three books:
There are many good online resources
On average, around 2300 avalanches are reported the CAIC every season. This includes natural, deliberately, and accidentally triggered avalanches. We estimate that 10 times that number of avalanches occur in Colorado each season, but go un-reported.
On average, avalanches kill six people in Colorado each year. There were 8 avalanche fatalities in the 2009-10 season. Over the past 10 years, the average number of people caught in avalanches was 60; over the last 15 years, the average is 65. In spite of Colorado’s rapid population growth and the accompanying increase in winter recreation, the average number of people caught has held steady or decreased slightly.
The CAIC investigates every fatal accident, and as many of the other accidents as possible. Accident reports are published so we can learn from the mistakes of others, or learn what went right.
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