Explainer: Know how avalanches are caused!

A fully developed avalanche can weigh up to one million tonnes and reach speeds of up to 320 km per hour.

When an unstable mass of snow detaches from a slope, it triggers an avalanche. As it descends, the snow accelerates, forming a powerful flow and a towering cloud of ice and snow that ascends high into the air. As it continues downhill, the avalanche gathers more snow, increasing its mass. A fully developed avalanche can weigh up to one million tonnes and reach speeds of up to 320 km per hour.

Avalanches are caused by a combination of factors related to snowpack stability, terrain characteristics, weather conditions, and human activities.The stability of the snowpack is a critical factor. Avalanches often occur when a weak layer of snow collapses under a stronger layer above it. This weak layer can form due to factors like temperature changes, wind loading, or the type of snow crystals present.

Weather plays a significant role in avalanche formation. Heavy snowfall can rapidly increase the weight of the snowpack, increasing the likelihood of instability. Rapid temperature changes, particularly warm temperatures after a period of cold weather, can weaken the snowpack and trigger avalanches.

The shape and steepness of the terrain contribute to avalanche risk. Slopes between 30 to 45 degrees are most prone to avalanches because they allow snow to accumulate and become unstable. Terrain features like gullies, cliffs, and convex slopes can also increase the risk by creating areas where snow can accumulate in unstable layers.

Human activities
Human activities, such as skiing, snowboarding, snowmobiling, and hiking, can trigger avalanches. The additional weight and movement of people can stress the snowpack, causing it to collapse and slide downhill. Activities that involve crossing or being on steep slopes increase the risk significantly.

Avalanches can also be triggered naturally by factors like earthquakes, wildlife movement, or even falling ice or rocks.