Avalanches are large snow slides sweeping down mountain slopes at high speed carrying trees, rocks and debris at great speed. Avalanches often kill people and destroy homes at incredible speed. Some can travel over 100 miles an hour with devastating results. Avalanches typically occur during the winter season when an unstable layer of snow becomes unstable and releases all at once; weather conditions, terrain features or human activity such as careless skiing/boarding can trigger an avalanche; natural events such as earthquakes or landslides also contribute to an avalanche’s potential cause.

Sluffs and slabs are the two primary types of avalanches. Sluffs involve small slides of powdery snow that travel down slope without ever leaving any trace behind them; slab avalanches occur when weak layers deeper within the snowpack cause all layers to collapse into one massive block known as a slab and descend en masse downslope as one huge slab, often more dangerous than their counterpart sluffs.

An avalanche is created when there is a combination of steep, unconsolidated snow layers, a weak spot in the snowpack and favorable weather conditions that combine to cause it. Snowpack specialists at avalanche centers regularly document snow conditions and combine this information with meteorological data to calculate an avalanche danger level that is then posted online and broadcast over radio – the higher this number is, the more likely avalanches are likely to happen and more destructive they are.

An avalanche begins at the top of a slope when unstable snow breaks loose from more stable portions and races down at great speed, carrying debris with it in an avalanche track all the way down until reaching its runout zone at the bottom of slope. An avalanche may also generate an air blast zone around its path that blows snow and sand into the air for hundreds of yards around its path, creating an air blast known as smoke zone.

Although avalanches tend to occur more often during winter, they can happen any time of the year and in certain locations can even be deadly in summer when there is deep and dense snowfall.

There are a number of steps you can take to lower the likelihood of becoming trapped in an avalanche. Avalanche prevention includes learning more about different types of avalanches, watching for signs of instability such as convex rolls on slopes, and avoiding leaning or overhanging trees. Ski areas employ avalanche control teams to minimize risk by initiating slides before skiers hit the slopes and using explosives to clear away any unsafe accumulations of snow. Forest rangers use similar tactics in remote mountain regions of Canada and Switzerland to protect villages and towns from snowslides. Avalanche experts also work in mining operations and military positions; backcountry skiers and snowboarders may also opt for using beacons and detectors to avoid potentially hazardous slopes.