Avalanches are powerful, unpredictable and can occur at any time. The best way to avoid an avalanche is to recognize the warning signs and to steer clear of avalanche-hazard areas. There are two types of snow avalanches: (1) Loose snow avalanches that begin in a small area, but grow larger, taking on more snow as they descend; and (2) Slab avalanches that start as a large slide. A slab avalanche usually has a well-defined fracture line where moving snow breaks away from stable snow. There are usually chunks or blocks of snow in the slide. The fracture line may be visible before the avalanche slides down the mountain. Avalanches are more likely to occur during or after a snowstorm if snow has been blowing and drifting because the "new" snow hasn’t bonded to the underlying snow pack and is unstable. Avalanches may occur on slopes ranging from 25 to 60 degrees. Snow on north-facing slopes is more dangerous in mid-winter. South-facing slopes are dangerous during spring, especially on sunny days. Historic avalanche areas can be identified by the lack of vegetation, such as trees or brush, or by where existing vegetation is bent or broken. Avalanche chutes are particularly noticeable in heavily forested areas because the snow path is void of the tree cover that surrounds it. A recreationist’s safest route is on a ridge top, slightly on the windward side and away from cornices. Cornices, the overhanging banks of snow on ridges, are more likely to develop on leeward slopes because the wind carries the snow from the windward slope over the ridgetop and deposits it on the leeward side. The next safest travel route is out in the valley, far from the bottom of slopes. Recreationists should not cross the lower part of slopes, especially long, open areas or known avalanche paths. Avoid disturbing cornices from above or below. Before recreating in avalanche country you should inspect and practice using your avalanche survival gear, which is a transceiver, probe pole and shovel. If you are caught in an avalanche:
- Discard all equipment and, if you are a snowmobiler, get away from your machine.
- Make swimming motions and try to stay on top of the snow; work your way to the side of the avalanche.
- As you feel the avalanche slow, try to thrust your hand or another part of your body above the snow surface.
- Before the snow settles, move your arm in front of your face to clear an air space.
- Try not to panic, you need to preserve oxygen.
If you are a survivor or an observer:
- Keep your eyes fixed on the moving mass of snow in which he or she is trapped.
- Mark the place where you last saw the victim.
- Search for the victim directly down slope from the last sighting when the snow stops moving. Use a probe pole, ski pole or stick to probe the snow.
- Stay with the victim unless help is only a few minutes away. After 30 minutes, the victim has only a 50 percent chance of survival.
- When the victim is found, treat him or her for hypothermia, suffocation and shock.
Avalanche advisory information is available from the U.S. Forest Service in the following areas: northwestern Montana: 800-526-5329; west-central Montana: 800-281-1030; and southwestern Montana: 406-587-6981. For more information about avalanches or winter recreation safety, contact: Montana Fish, Wildlife & Parks, Conservation Education Division, PO Box 200701, Helena, MT 59620-0701; or call 406-444-7317.
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