Snowflakes and Avalanches

05102237

High on a mountainside, ski patroller Karl Birkeland dug a pit into a drift to check the snow's stability. He declared the slope safe for skiing. The danger of an avalanche appeared low.
It was 1985, and Birkeland was out with friends near the Snowbasin ski area in Utah. After he tested the drift, the skiers set off down the mountain. \"I let my guard down and skied out of sight of the others,\" Birkeland says.

That was a big mistake. The snow started to break and slide, creating an avalanche that threatened to bury him.

\"Unbeknownst to us, the snow changed quite a bit from where we dug the pit,\" Birkeland says. \"It was pretty terrifying,\" he recalls. \"I didn't have anyone watching me.\"

Birkeland was lucky that day. He managed to ski out of danger, and the avalanche passed him by.




An avalanche roars down a mountainside.

National Park Service



Some people are less fortunate. Every year, avalanches kill as many as 30 people in the United States and more than 150 people worldwide, including experienced skiers, snowboarders, and mountaineers. And the numbers are going up.

Avalanches are masses of snow and ice that slide down mountains. In the past, predicting such movements was mostly a matter of guesswork. To make better predictions, scientists are now analyzing ice crystals, studying snow-stability patterns, and looking for connections between weather and avalanche danger. Protecting people from the dangers of avalanches is a major goal of this research.

Snowflake crunch

Snowflakes appear soft and delicate as they fall. But once the icy flakes get packed together on the ground, they can turn into a destructive force of nature.

An ice block that measures 3 feet on each side can weigh 1,000 pounds, says Birkeland, who's now an avalanche scientist at the U.S. Forest Service National Avalanche Center in Bozeman, Mont. The snow in an avalanche measuring 3 feet deep, 100 yards long, and 50 yards across could weigh a crushing 5 million pounds.




Karl Birkeland examines snow crystals as he stands in a snow pit in Montana's Bridger Range.

Photo by Ron Johnson



As an avalanche moves, it picks up nearly anything in its path, including rocks and other debris that can smack a skier senseless. Once a person is buried, it can be nearly impossible to get out of the snow without help. Suffocation often follows.

Snowflakes are crystals of ice. They often have a lacy, six-sided shape. But, Birkeland says, \"the minute they touch the ground, snow crystals start changing.\"

Depending on the temperature of the air and ground, snow crystals change size and shape. Some stick. Some don't. Snow can be soft, slippery, wet, or icy, and it can change quickly as weather conditions change.

\"The snowpack is a very dynamic thing,\" says Jeff Dozier. He's a snow researcher at the University of California, Santa Barbara.

Experienced skiers know how tricky snow can be. They have various words to describe the types of snow they may run into: sugar, corn, powder, grapple, champagne, foof, mashed potatoes, Sierra cement, and more.