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Precautions in snowy terrain

Snow safety includes precautions in snowy terrain, except those for cold weather.

AvalanchesEdit

 
Avalanche in Switzerland. Note the ski lift building in the foreground for scale.
 
Easy way to assess slope, 30° or more involves risk

Avalanches are a danger of mountain areas. At winter resorts the risk of avalanches is monitored and warnings given when the risk is high.

Avalanches are not an abnormality; steep slopes can hold only so much slow, and the excess volumes will come down as avalanches. The problem is that snow is sticky, so it needs some triggering to come down, and some snow coming down can be the triggering event for the rest. Sometimes the original trigging event is the sun warming the snow, sometimes some more snowfall, sometimes other natural events, often a human. The risk for avalanches depends also on the structure of the snow. Layering can facilitate upper layers gliding down on lower layers, or a middle layer can collapse (progressing over a large area) causing the upper layers to glide down.

Most accidents happen when people go downhill off piste – the risk of being a victim of a spontaneous avalanche is much smaller than the risk of actually causing an avalanche (or getting in the way of one started by others). When the risk is high, also spontaneous avalanches will still happen.

In addition to off piste skiing, other disturbances may start an avalanche e.g. driving a snowmobile.

If going off piste despite warnings you should know how to evaluate the current risks, avoid them where possible, and have safety equipment and know how to increase your survival chances would you be unlucky.

Avalanches start on slopes steeper than 30° (50 %) grade, roughly the same as traditional, moderately pitched roofs in Norway and Northern Europe. If you go back-country skiing or off-piste skiing, learn how to gauge the steepness. If in doubt, don't do it. Once started, the avalanche can run down 20–30° slopes, and some distance over level terrain or even uphill. An avalanche never reaches further than 20° from the starting point. Avalanche hazard depends on local conditions, ask locals for advice.

Those moving in terrain prone to avalanches can reduce risks by choosing their path: avoiding weak areas where it is easy to cause an avalanche, and avoiding areas where being hit is easy or especially dangerous because of likeliness of being trapped, hurt by obstacles, swept over cliffs etc. Narrow river valleys or gullies can be "avalanche traps" and even small avalanches can be fatal. Wind-swept ridges with little snow are among the safest places to move.

Where an avalanche is possible, a group should move one by one, so that only one is likely to be hit if it does occur, leaving the others ready to call for help, and start searching or give first aid. A tight group of skiers is also more likely to cause an avalanche than several individual ones. Ensure good communication, so that everybody is aware of and understands decisions made.

Risk factorsEdit

 
Wind-swept ridges are safe, cornices are not
  • Layered snow
  • Snow cornice
  • Wind
  • Snowfall, rainfall
  • Rising temperature, sunlight
  • Skiing
  • Narrow river valleys

Safety equipmentEdit

  • Warm dressing, to delay hypothermia if buried
  • Avalanche transceiver (beacon): sends signals at regular intervals, enabling locating you under the snow; use purpose made modern ones and get at least some training in how to use them
  • Collapsible probe
  • Sturdy shovel: the energy of the avalanche causes the debris to pack dense and hard, even when the snow was powder before

(Avalanche cords are obsolete.)

In case of an avalancheEdit

 
Skiing is fun but not without risk on steep slopes

Try to get away from the path of the avalanche. Have a wide stand, ski in a 45° angle to the slope and aim for high ground. If you are caught, get rid of skis, poles and large packs. Fight for the surface and create an air pocket in front of your face. When the avalanche stops, the snow will suddenly freeze, making any movement nearly impossible. Stay calm and wait for rescue. If you are very close to the surface you may be able to get a hand through the snow, but this is unlikely.

If your company is hit, those buried should be found quickly; the first ten to twenty minutes survival is very likely, while only some survive for more than two hours. Thus effective companion rescue is paramount. Immediately calling for help is still important: the rescued victims can be injured or otherwise in need of medical help, and there is still a chance for a victim to survive long enough under the snow to be rescued by the arriving team.

Assess whether there is a risk of further avalanches and take safety measures as appropriate. Check how many are missing and where they were last seen. Call for help. Check any clues about where they might be buried, mark the position. Turn the switch to make the beacons receive instead of transmit. Plan how to search and whether some areas should be prioritized. Be systematic without unnecessarily loosing time.

The beacons can be used for locating a buried victim (i.e. the victim's beacon). The signal should be quite reliably received from about 20 m. The beacons are quite easy to use, but training and regular practice is needed for using them effectively.

Digging out the victim is time consuming and should be efficient while safe for the victim. Avoid standing on the victim, not to destroy any air pocket or compressing the chest cavity. Digging out a "V" downhill from the victim may be the best tactic, tallness 1–2 times the depth depending on terrain steepness.

Covered dangersEdit

Snow covers features of the landscape, including clefts, streams and other dangers. Be sure to know where you are to avoid them, rather than relying on what you see. On glaciers rope is used to stop somebody falling into a cleft, but this requires some know-how, for best protection and to avoid everybody being dragged into it. Do not go near the rim of a drop, as the snow may extend further than the cliff, or may collapse.

Low visibilityEdit

Thick snowfall can bring visibility down to a few metres. Even light snowfall considerably lessens visibility, so that distant landmarks can get out of sight. Wind-drift lower visibility in a similar manner near the ground.

Snow blindnessEdit

See also: Eye care
 
Goggles used by Inuits.

Snow blindness is a variant of ultraviolet keratitis, caused by extreme levels of ultraviolet light reflected by snow, similar to sunburn. Sunglasses with good UV protection are the very least you should do to protect yourself. Emergency lenses can be made by cutting slits in dark fabric or tape folded back onto itself.

Symptoms usually come hours after the exposure. Treatment is covering the eyes to let them rest, and possibly pain relief (remove contact lenses). Trekking as blind is not nice, but may be better than worsening the condition. Consider stopping as soon as you can at safe shelter to recover (with eyes covered). The eyes usually recover in one to three days.

See alsoEdit

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