Les avalanches ne sont peut-être pas la première chose à laquelle vous pensez lorsque vous explorez les montagnes, mais savoir comment se protéger contre les avalanches est un aspect important des sports d'hiver en montagne.
Cette page explique brièvement certaines des notions les plus importantes à connaître avant de partir. Si vous souhaitez en savoir plus, nous vous recommandons de suivre notre tutoriel en ligne, Avy Savvy, avant de suivre une formation de sécurité en avalanche offerte par Avalanche Canada.
Most avalanches happen on slopes that are between 30° and 45°.
Convex rolls on a slope are trigger points—places where avalanches are likely to start. You can also be at risk when you are directly under these convex rolls.
Cornices develop when wind-deposited snow forms an overhanging shelf along ridges and above slopes. Cornices are unstable and should be avoided, whether you are on the ridge, or below it.
In a forested area, avalanche paths are identified by the openings in the trees. In the alpine, avalanche paths are identified by slope steepness and shape. Even if you are on low-angle or flat terrain, it’s important to always be aware of the possibility of avalanche slopes above you.
You don't have to be doing anything extreme in the mountains to find yourself in avalanche terrain, as this video demonstrates. Calgary Realtor Bryon Howard was running on a trail around Lake Louise, Alberta, when an avalanche came down a slope across the valley from him. Fortunately the avalanche wasn't a very big one and he was only dusted by the powder cloud. However, that slope can easily produce much bigger avalanches, and the results could have been much more serious. This is a great example of the need to be aware of not only where you are, but also what’s above you.
A terrain trap is any terrain feature that makes the consequence of an avalanche more serious. Steep-sided depressions, such as gullies, creek beds, and ditches will trap moving snow and cause the avalanche to accumulate much more deeply in a small area. Trees, rocks, and cliffs can lead to greater injury if you’re caught in an avalanche.
Terrain traps might include:
Gullies, creek beds, ditches
Flat areas under steep slopes
Trees or rocks in slide paths
Look for signs at the trailhead that warn you of avalanche terrain. These signs indicate which areas are more, or less likely to produce avalanches. These signs do not exist at all trailheads. In the mountains, you are likely to encounter avalanche terrain in areas that don't have warning signs.
Avalanches are more likely when there has been:
Heavy snow is when 30 cm or more falls over 48 hours, or if 2 cm of snow (or more) has fallen every hour for several hours.
Strong sunshine, warm temperatures, and rain all have a destabilizing effect on the snow. The first warming (close to 0° or warmer) after a storm is often when avalanches occur.
There are some warning signs you can look and listen out for that tell you the snowpack is unstable and avalanches are more likely. If you see or hear any of these signs, it is best to stay away from avalanche terrain and avoid being under any areas that might avalanche. If you don't see any signs of instability, it does not mean that avalanches are not possible.
If you see cracks shooting out from under your weight, that is a clear sign of unstable snow.
If you witness avalanches, or see signs of recent avalanche activity, that is a sign of instability.
A whumpf is the sound the snowpack makes when layers are collapsing within it. It sounds exactly like the word sounds. Whumpfs indicate instability and can signal the start of an avalanche in avalanche terrain.
The avalanche forecast tells you how likely avalanches might be on a certain day in a certain area, based on the snowpack and the weather forecast. You can find the danger rating at the top of the forecast. This is the first place to look before planning your trip.