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Different types of avalanches exist and are generally classified according to their physical characteristics. An avalanche can release from a single point or a whole area (loose or slab); it may be the whole snow cover or only part of it that slides (full or partial depth); and it can be channelled or not (confined or unconfined). It may also be airborne or flow along the ground.

A full-depth avalanche on The Great Slab, Coire an Lochain

Avalanches are initiated because of either changing internal factors, such as bonds between layers being weakened by rising temperatures, or external factors, such as snowfall or a person walking or skiing on the slope. The details of the release process are complex and poorly understood. However, some basic principles are well known. Avalanches can release on slopes between about 20° and 60°, although slopes between 30° and 45° are the most likely to release, with about 38° being the optimum angle for slab avalanches. Above about 60° snow tends to slide off in small sluffs rather than building up to reach dangerous quantities. The greatest danger usually exists during and for approximately 24 hours after a period of heavy snowfall. This danger period is longer in cold temperatures, when the snow consolidates more slowly. Thaws, especially if accompanied by rain, produce a wet-snow hazard, as well as the danger of collapsing cornices. Even in the absence of snowfall or thaw, a significant avalanche hazard may be created by the wind redepositing the snowpack.