If plan on going outside to hike this winter or spring in snow-covered terrain, you need to consider avalanches as a viable hazard. An avalanche occurs in mountainous or even hilly terrain when snow and ice suddenly cascades down a slope. Each year, avalanches cause many fatalities, with hikers, snowmobilers, and skiers as the most common victims of avalanche fatalities.

As a first defense against avalanche hazards, use your brain.

Knowledge of the “Avalanche Triangle” can help you make an intelligent, informed decision about whether or not you are at risk of being harmed by an avalanche. The three components of the avalanche triangle include terrain, weather, and snowpack. But consider yourself the human factor in the middle of this triangle, as your presence in avalanche territory is what ultimately puts you in danger.

The Avalanche Triangle: Terrain

Terrain is a key factor to consider when deciding whether or not you are at risk of encountering an avalanche. Most avalanches occur on slopes whose angles are between 30 and 55 degrees, and specific terrain features may also make a slope more prone to avalanche than its steepness alone.

Common avalanche trigger points include a cornice, an overhanging snow feature, which could break off and trigger an avalanche on the slope below. Convex slopes are also generally more hazardous that convex or uniform slopes, and the leeward side of a slope will be more dangerous that the windward side of a slope, especially following a snowstorm.

Look out for snow pillows and depressions near rocks and trees, as these areas may be more prone to avalanche than other more uniform and open areas.

Choosing to travel across a ridge is usually safer than choosing to travel below a steep slope or in a gully, which will act as a funnel in the event of an avalanche. Avoid traveling in the area of other terrain traps, which include abrupt changes in the steepness of the terrain. Trees, cliffs, and icefalls area also considered terrain traps because these terrain features could cause increased trauma to a person swept over or through them.

If you know you will need to cross, ascend, or descend a slope that matches these terrain characteristics, think carefully about the other factors below, and consider taking an alternate route or planning your trip for another day on which the avalanche danger is lower.

The Avalanche Triangle: Weather

Several weather variables affect the likelihood of avalanches, so always be sure to check weather and avalanche forecasts before setting out into avalanche-prone terrain. Amount of snowfall, temperature, wind speed, and wind direction are all factors that you should consider, as changing weather and recent snowfall can quickly create unstable conditions.

Use extreme caution when travelling during or following a storm with high winds and a large amount of snowfall, as the avalanche hazard is higher at these times. Sun-exposed slopes and warmer temperatures may mean more stable conditions in the winter, but sun-exposed slopes may be more at risk for avalanches in the spring due to rapid warming and melting patterns. Wind generally picks up snow from the upwind, or windward, side of a slope and deposits it on the leeward side. Therefore, leeward slopes are usually less stable.

The Avalanche Triangle: Snowpack

As snow accumulates on a slope, it settles in layers. Snowpack is the term that describes how snow accumulates, settles, and bonds between layers. Factors such as snow density, temperature, wind, ground vapor, snow depth, and snow structure can all affect the stability of the snowpack.

Spatial variability, or change in snow from top to bottom, is important to consider when assessing an area for avalanche danger. As the snowpack forms in layers, some of those layers may be weaker in others. Granular snow, sometimes called sugar snow, for instance, may not bond well to others layers of snow. Other areas may be weakened by rotten snow or irregular melting patterns. Weak areas in the snowpack can become more dangerous when combined with the other terrain and weather factors that contribute to avalanches.

Terrain, weather, and snowpack are the three key elements that contribute to Avalanche Triangle, but don’t forget that you--the human factor--are the most important element of all. Go into the backcountry with the necessary knowledge and tools you need to assess avalanche risk, and be willing to turn around or alter your route if you’re not willing to accept the consequences.