Terrain Factors

Recognizing avalanche terrain and terrain traps is crucial to reduce the likelihood and severity of being caught in an avalanche.

Weather, snowpack, and people's decision-making are dynamic factors constantly changing and filled with uncertainty. The terrain on the other hand is a static variable and is therefore possible to plan for possible dangers in advance. Recognizing avalanche terrain is therefore crucial and could prevent the possibility and severity of an avalanche. However, identifying when the terrain presents avalanche danger is complicated and depends on multiple variables.

Slope Angle

The angle of the slope is the most significant terrain characteristic that determines whether an avalanche can occur or not. When the slope gets steeper the forces of gravity on the snow increase. Avalanches most commonly occur on slopes between 25° and 45°, and around 97% of all avalanches occur on slopes steeper than 30°. When the slope is less than 25°, the force of gravity isn’t strong enough to pull the snow down the mountain, no matter how instable the snowpack. For slopes greater than 45° the snow has a hard time bonding and it is rare that enough snow accumulates to form a slab.

Credit: Varsom - Norwegian Avalanche Center

Terrain Traps

Distinct terrain features increase the consequences of getting caught in an avalanche - often referred to as terrain traps. If terrain traps are present, even a small slide could potentially result in serious consequences. Terrain traps like walls in a couloir, cliffs, and trees can lead to higher trauma during the avalanche itself. Whereas cornices and gulleys can both contribute to a higher probability of being deeply buried after the avalanche has stopped. Not every terrain trap is possible to identify on a map or at a distance, so it’s critical to be alert to traps you encounter along your tour, and so that you can change your route if necessary.

Slope Shape

You are most likely to trigger an avalanche on convex shaped mountains - where the terrain starts flat at the summit and gradually gets steeper. Snowpacks on a these kinds of mountains have high levels of tension in all layers of the snowpack, meaning that their weakest layers become easier to trigger. Concave shaped slopes, on the other hand, have low levels of tension in their snowpack, and are often easier to plan around dangers given that the rider can often see the bottom of the slope from the very top. The slope shape is also important for where the snow settles during wind transportation and cornice formation. Wind slabs and cornices form on the “leeward” side of the mountain or ridge-line - or the direction which wind is going. Winds traveling from west to east will deposit snow on the eastern slopes of the mountain.

Other avalanche factors...

Weather Factors

Temperature, wind activity, and loading of new snow can all impact the stability of the snowpack on any given day.

Snowpack

Understanding the composition of the snowpack is critical to understanding the risk of avalanches occurring.

Human Factors

At the end of the day, you are the one making the final decision based on your knowledge, experience and the influence from other people in your party.

Slab Avalanches

A slab avalanche is an avalanche that loosens as a large, cohesive area of snow of snow and slides downwards.

Loose Snow Avalanches

A loose snow avalanche is an avalanche that releases from a single point and spreads downwards in a cone shape.

Find an Avalanche Course

This information is meant to be an introduction to avalanche safety and a knowledge base for backcountry travelers.

But reading it cannot replace real experience in reading conditions and making decisions in the field. We strongly recommend that all backcountry travelers take instructor-led avalanche courses to get hands-on experience in wild snowpacks.