Also known as "snowslides", an avalanche is a mass of snow sliding down a mountainside. Avalanches can occur in any situation where snow, slope and weather conditions combine to create proper conditions. Adirondack backcountry recreational users should know that avalanche danger does exist in New York. This web page and the accompanying brochure provide the basic ideas of what to look for and avoid. To learn more about avalanche awareness, consider attending professional courses.
- Know basic avalanche rescue techniques. Visit the National Avalanche Center's webpage (leaves DEC website) for more information.
- Check the snow depth.
- Check how much new snow has fallen.
- Practice safe route finding.
- Check the degree of the slope.
- Check the terrain.
- Carry basic avalanche rescue equipment.
- Never travel alone.
- Let someone know where you are going.
- Do not be afraid to turn around.
- Use common sense.
An avalanche occurs when the stress (from gravity) trying to pull the snow downhill exceeds the strength (from bonds between snow grains) of the snow cover. Four conditions must be present for an avalanche to occur:
- a steep slope,
- snow cover,
- a weak layer in the snow cover, and
- a trigger.
Avalanche danger increases with major snowstorms and periods of thaw. About 2,000 avalanches are reported to the U.S. Forest Service Avalanche Center in an average winter. More than 80 percent of these occur during or just after large snowstorms. The most avalanche-prone months are, in order, February, March, and January. Avalanches caused by thaw occur most often in April.
About 90 percent of all avalanches start on slopes of 30-45 degrees; about 98 percent of all avalanches occur on slopes of 25-50 degrees. Avalanches release most often on slopes above timberline that face away from prevailing winds. This is because leeward slopes collect snow blowing from the windward sides of ridges. Avalanches can occur, however, on small slopes well below timberline, such as gullies, road cuts and small openings in the trees. Very dense trees can anchor the snow to steep slopes and prevent avalanches from starting, however, avalanches can release and travel through a moderately dense forest. Most avalanches occur in the backcountry, outside of developed ski areas.
How to Minimize Risk
You can reliably avoid avalanches by recognizing and avoiding avalanche terrain. Travel on the valley floor away from large avalanche runouts, along ridgetops above avalanche paths, in dense timber, or on slopes of 25 degrees or less that do not have steeper slopes above them. Avoid cornices, or hanging masses of hardened snow.
You cannot entirely eliminate risk if you travel in avalanche terrain, but you can minimize risk by using good technique: climb, descend, or cross avalanche areas one at a time; cross a slope at the very top or bottom if possible; climb or descend the edge of a slope rather than the center; carry and know how to use avalanche rescue gear; and turn back or alter your route if you detect signs of unstable snow.
Signs of Danger
When the snow cover is very unstable, nature often broadcasts clear danger signals. Fresh avalanches are the best clue. Snow that cracks, collapses, or makes hollow sounds is also unstable. Weak layers that are found by digging snow pits are signs of unstable snow. Snow that has become wet from thaw or rain can be dangerous.
Even if you find no signs of unstable snow, you should always travel observing the techniques listed above to minimize risk.
You should always have an avalanche transceiver (or beacon), shovel, and a collapsible or ski-pole probe. You should practice frequently to be proficient in using your beacon. However, you should not take extra risk just because you have rescue equipment. Always carry a day pack with enough equipment to spend the night.
What to do if You're Caught in an Avalanche
Surviving avalanches can depend on luck, but it is always better to avoid them in the first place. Remember that only 1 of 3 victims buried without a beacon survives. If you are caught, first try to escape to the side, or grab a tree or rock. If you are knocked down, get rid of your poles, skis, and a heavy pack. Swim with the avalanche to try to stay on top and avoid trees. When the avalanche slows down, reach the surface or make an airpocket.
Safe Travel Techniques
- Never put everyone on the slope. Only one person should be on the slope at a time.
- Have an escape route planned. Always think avalanche. What will you do if the slope slides. Have a plan before you travel.
- Use slope cuts. Keep your speed up and cut across the starting zone, so that if the slope slides, your momentum can carry you off the moving slab into safer terrain. You can do this on skis, snowboards or on snowmobiles.
- Watch out for cornices, which tend to break farther back than expected. Always give them a wide berth. NEVER walk out to the edge of a drop-off without first checking it out. Many people have died this way.
- If it looks too dangerous, find a safer route. Use terrain to your advantage. Follow ridges, thick trees and slopes with safer consequences. You can almost always go back the way you came. The route got you there, it will most likely get you back as well.
- If there's no other choice, go underground. You can almost always weather out a bad storm or bad avalanche by digging a snow cave or seeking the shelter of a crevasse. You may be uncomfortable but you will be alive.