Colorado most dangerous state in nation for avalanche fatalities

December 27, 1999

Avalanches in the state have already claimed the lives of three people this winter, a somber reminder of the risks that hikers, skiers, snowboarders and snowmobilers face in the Colorado mountains.

In the United States, 514 avalanche fatalities were reported in 15 states from 1950 to 1997. Colorado has the dubious distinction of claiming about one third of those deaths, said Richard Armstrong, a glaciologist and avalanche expert at the CU-headquartered National Snow and Ice Data Center.

"In looking at the long-term statistics on avalanche fatalities, Colorado has about twice the number people killed than Alaska, the next highest-ranking state," he said. "While there is a lot of variability in avalanche fatalities from year to year, we have the dubious distinction of leading the nation."

Each year avalanches claim more than 150 lives worldwide. The numbers have steadily increased over the past few decades with the increased popularity of winter sports such as backcountry skiing and snowmobiling, said Armstrong. To assist with preparedness, the NSIDC has posted avalanche awareness information on its Internet home page at:

The site discusses avalanche basics such as ways to evaluate snowpack stability, recognize danger signals and evaluate survival gear. It also offers links to related sources, said NSIDC Outreach Coordinator Annette Varani.

Following is a short summary of avalanche information posted by NSIDC, which is part of the Cooperative Institute for Research in Environmental Sciences. CIRES is a joint venture of CU and the National Oceanic and Atmospheric Administration.

* According to the Colorado Avalanche Information Center, 89 percent of avalanche victims are men and most victims are between the ages of 20-29. About 75 percent are experienced backcountry recreationists. Climbers, backcountry skiers and snowmobilers are by far the most likely to be involved in an avalanche.

* A coarse, grainy form of snow crystal known as "depth hoar" is often the culprit underlying avalanches. Because of its sand-like structure, depth hoar bonds poorly to other snow layers and creates a very weak layer in the snowpack. Conditions that produce depth hoar most often occur early in the season, and the weak layers are buried under subsequent snows. All too often, depth hoar layers are discovered only after an avalanche has swept off the overlying layers.

* Backcountry recreationists are most likely to trigger avalanches as they cross hazardous terrain. Traveling across steep slopes should be done cautiously, without spending too much time on them. Also to be avoided are avalanche "chutes," where large vertical swaths of trees are missing from a slope or chute-like clearings.

* Although avalanches can occur on any slope given the right conditions, certain times of the year and certain locations are naturally more dangerous than others. Most avalanches "run" from December to April, although avalanche fatalities have been recorded during every month of the year in Colorado.

* The highest number of fatalities occur in January, February and March, when the snowfall amounts are highest in most mountain areas. A significant number of deaths occur in May and June, demonstrating the hidden danger behind spring snows and the melting season that catches many recreationists off-guard.

* Avalanches are most likely to run either during or immediately after a significant snowfall. The 24 hours following a heavy snowstorm are the most critical. Temperature, wind and snowfall during storms can create fatal avalanche conditions.

* Most avalanches occur on slopes between 30 degrees and 45 degrees, but can occur on any slope angle given the right conditions. Very wet snow is well lubricated with water, meaning it can run on a slope of only 10 degrees to 25 degrees. Compacted, well-bonded layers of snow can cling to steeper slopes until a weak layer is created.

* New snowfall puts extra strain on the existing snowpack, especially if it does not adequately bond to the pre-existing surface layer. The extra weight of new snow can cause a slab to break off and slide. Amounts of six inches or more pose the largest threat to skiers and recreationists.

* Conditions like temperature and snowpack can change on a daily or even hourly basis. Weather changes such as warm fronts can gradually increase temperatures that cause melting within the snowpack. This can weaken the upper layers of snow, increasing avalanche potential.

* In between snows, rising temperatures may partially melt exposed surface layers which often re-freeze and create a slicker, less stable surface for the next snowfall. Light snowfalls and cold temperatures help strengthen the snowpack and make it more resistant to avalanches.

* Although avalanches will run on slopes facing any direction, most avalanches run on slopes facing north, east and northeast. Slopes that are under shadows throughout most of the day are more dangerous because the snowpack undergoes less melting and bonding that can make the snow layers stronger. Bowls and gullies can be dangerous at any time because snow can accumulate deeply and quickly in these areas.

* There are ways to gauge snowpack stability. Look for cracks shooting across the surface, or small slabs shearing off. These are signs of weakened snowpack. Also, listen for "hollow" or "whumping" noises as you walk or ski. This indicates that there is a weaker layer underneath, leaving the surface layer more prone to collapse.

* Avalanche victims usually die from either trauma caused by collisions with rocks or trees or suffocate after they are buried by snow. Avalanche beacons are the most commonly used rescue device and provide the fastest way of locating a victim when used by people properly trained with such equipment. When a victim is buried, the beacon emits a frequency that other beacons can home in on. It is critical to have your beacon set to "transmit" during your outing.

* Beacons, ski-poles, collapsable probes and shovels are a necessary part of your backcountry gear. Carrying this equipment may mean the difference between life and death for someone buried in an avalanche. Statistics show that most survivors are dug out within 15 to 30 minutes.

* If you are caught in an avalanche, yell and let go of ski poles and get out of your pack to make yourself lighter. Use "swimming" motions, thrusting upward to try to stay near the surface of the snow. If you are buried over your head, try to maintain an air pocket in front of your face by punching into the snow. Keeping your breathing steady will help preserve your air space and extend your survival chances.

University of Colorado at Boulder

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