FOR AVOIDING AND SURVIVING SNOW AVALANCHES
AVALANCHE CONDITIONS – RULES OF THUMB
Snow avalanches may release tremendous forces and are a serious threat to the winter traveler. If you are involved with one and, in particular, if you are buried, you will probably not survive. It is most important that you learn enough about avalanches to avoid them and to increase your chances of survival if you are caught.
There are many factors that contribute to avalanche conditions. The possible combinations and inter-relationships of these factors are countless and the forecasting of avalanche danger will often require the evaluation of a very complicated situation. However, there are many practical things you can learn that will be helpful to you.
The following general guidelines must not be accepted as absolute rules. They are only an organized list that a thinking observer can use to develop an opinion about the presence and degree of danger.
Slope steepness – Slopes of 30-45 degrees (60-100%) are most likely to avalanche, but anything from 25-60 degrees (46-170%), or even more or less, can do so under certain conditions.
Slope profile – Convex slopes are the most dangerous. Concave slopes are less dangerous, but they can, and sometimes do, avalanche.
Slope aspect – North-facing slopes are the most likely to avalanche during the middle of winter. South-facing slopes become dangerous in the spring and during sunny days as the sun begins to rise higher in the sky.
Leeward slopes are dangerous because wind borne snow adds to rapid accumulation of depth; also, the hard, hollow- sounding wind slab may develop there. Windward slopes generally have less snow and benefit from wind compaction.
Ground cover – Areas with large rocks, trees and heavy brush help to anchor the snow on the mountain. Smooth, grassy slopes are much more dangerous.
New Snow – You should always suspect dangerous conditions with a foot-of new snow. However, conditions can be dangerous with less snow.
Rapid snow settlement is a favorable sign. Look for settlement cones around tree trunks and over rocks. Lack of settlement is a danger sign.
Loose, dry snows avalanche easily. Moist, dense snows tend to settle rapidly, but during windy periods can also be dangerous.
Old Snow – When the old snow depth is sufficient to cover natural anchors, such as rocks and brush, additional snow layers will slide more readily. Also, the nature of the old snow surface is important; rough surfaces being favorable for stability and smooth surfaces such as sun crusts being unfavorable.
A loose, underlying snow layer is more dangerous than a compacted one. You can check this with a ski pole, ski, or snowshoe.
Crystal Types – You can readily observe general crystal types by letting them fall on a dark ski mitt or parka sleeve. Small crystals, such as needles and pellets, result in more dangerous conditions than the usual star-shaped crystals.
Wind – Sustained winds of 15 m.p.h. and over during a storm cause danger to increase rapidly.
Snow plumes from ridges and peaks indicate that snow is being moved onto leeward slopes during clear weather and that dangerous conditions may be developing, even though it is not storming.
Temperature – Snow persists in an unstable condition longer under cold temperatures. It settles and stabilizes more rapidly during warmer weather, near or above freezing.
High and rapidly rising temperatures in the spring months may result in wet snow slides, particularly from south- facing slopes.
Beware of a rapid rise or fall of temperature. Shadows creeping across a slope may change temperatures enough to create dangerous conditions.
Rate of Snowfall – Snow falling at the rate of one inch per hour or more increases avalanche danger rapidly.
Old Slide Paths – An avalanche path that has slid once will slide again. Look for old scars in timber and avoid steep gullies and steep, open slopes.
Sluffing – Sluffing indicates that stabilization is taking place.
Recent Avalanche Activity – Look around, if you see new avalanches you should suspect dangerous conditions.
Sound and Cracks – If the snow sounds hollow, particularly on a leeward slope,conditions are probably dangerous; if the snow cover cracks and the cracks run in the snow, slab avalanche danger is high.
Check weather forecasts. Contact U. S. Forest Service Snow Ranger or the nearest winter sports area ski patrol.
Route Selection and Precaution – Rules of Thumb
The safest routes are on ridge tops and slightly on the windward side away from cornices.
Windward slopes are almost always safer than leeward slopes.
If you cannot travel on ridges, the next safest route is out in the valley away from the bottom part of slopes.
Stay high and near the top if you must cross dangerous slopes or avalanche paths; if you can see old or new avalanche fracture lines, be sure to avoid them and other similar areas.
Go straight up or down if you must ascend or descend a dangerous slope; do not make traverses back and forth across it.
Take advantage of areas of dense timber, ridges or rocky outcrops as islands of safety. Use them for lunch and rest stops and spend the least time possible out on the open slopes.
Snowmobiles must not travel across the lower part of slopes; especially long, open slopes or known avalanche paths.
Look for, and obey, all signs or other warnings of avalanche danger.
Avalanche Involvement – Rules of Thumb
Only one person at a time on a suspect slope: all others watch the person that may be in danger.
Remove ski pole straps, ski safety straps, loosen all equipment, put on mitts, cap, and fasten clothing before being exposed to avalanche danger.
Carry and use an avalanche cord, carry a sectional probe.
If Caught in an Avalanche
Discard all equipment.
Get away from your snowmobile.
Make swimming motions, try to stay on top and work your way to the side of the avalanche.
Do not cry out or open your mouth after you are in the avalanche.
Get your hands in front of your face and try to make an air space as you are coming to a stop.
If you are the Survivor
Mark the place where you last saw the victim.
Search for him in the fall line and directly below the last seen point.
Search the area of greatest deposition first.
You are his best hope for survival. Do not desert him and go for help unless help is only a few minutes away.
Remember, you must consider not only the time for you to get to help, but the time required for help to return, and the victim has only a 50% chance of surviving for an hour.
If you go for help, mark the route so a rescue party can follow it back.