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A million tons (1,016,050,000 kilograms) of snow rumble eight miles (13 kilometers) downhill, kicking up a cloud of snow dust visible a hundred miles (161 kilometers) away.
This is not a scene from a disaster movie—this describes reality one day in April 1981. The mountain was Mount Sanford in Alaska, and the event was one of history's bigger avalanches. Amazingly no one was hurt, and luckily avalanches that big are rare.
An avalanche is a moving mass of snow that may contain ice, soil, rocks, and uprooted trees. The height of a mountain, the steepness of its slope, and the type of snow lying on it all help determine the likelihood of an avalanche.
Avalanches begin when an unstable mass of snow breaks away from a mountainside and moves downhill. The growing river of snow picks up speed as it rushes down the mountain. Avalanches have been known to reach speeds of 245 miles an hour (394 kilometers per hour)—about four times as fast as the speediest downhill skier.
This winter in the western United States alone, about 100,000 avalanches will tumble down mountainsides. In the United States and Canada crashing walls of white will bowl over about 300 people. Most will be skiers, snowboarders, or snowmobilers who set out to have fun. Many will be buried by snow. Most will survive; some will not.
Text by Allan Fallow
Photograph above by Galen Rowell/Corbis
Photograph at right by AFP/Corbis
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