An avalanche is a swift-moving mass of snow and other materials such as rocks or earth that is propelled at high speed by gravity, usually occurring in mountainous regions with persistent, deep snowpacks and can be one of the most dangerous natural hazards to people living nearby. They typically occur between December and April (in the Northern Hemisphere) but can occur year-round.

An avalanche requires certain conditions in order to occur: a steep slope, layers of snow and pressure from weight, wind, rain or movement exerted upon these layers from weight, wind, rain or movement exerted from weight or body pressure or movement. Once these conditions have been fulfilled an avalanche may be set off downslope quickly taking trees and boulders with it as it moves rapidly along. Its path often creates chaos which results in serious injury and death to both victims and innocent bystanders alike.

There are various kinds of avalanches, each classified by their origin point, path and material transport method. An avalanche path can either be open or channeled, smooth or steep and narrow – wet or dry conditions also play a factor; loose material or dense accumulations, with surfaces either clean or covered by rock and wood debris can result in different kinds of avalanches occurring at various speeds; large and small avalanches alike can occur simultaneously or rapidly over a short distance.

Avalanches can be caused by human activities and weather; however, heavy snowfall with strong winds is the most likely to trigger them. An overloaded snowpack often ruptures under this strain as its weak links break apart under strain; other weather events that could be triggers include sudden warming of existing snowpack, heavy or intense rainfall on existing snow, or new precipitation that quickly turns from water into ice precipitation.

Once an avalanche is initiated, its danger can increase with every passing moment. While its path may be hard to follow, clues such as clear zones and lack of fallen tree trunks and branches may help people navigate to safety more quickly. Avalanches can also be stopped by throwing objects into its flow to deflect its flow or using explosives to detonate snowpack.

An avalanche that carries people downhill causes many deaths each year, with trauma being the primary cause. An avalanche can also bury victims deep beneath snow layers, leading to slow suffocation that may prove fatal – this is why having a survival plan and trained rescue team in case an avalanche occurs is so critical. Survival chances also change over time: peaking midday before dropping at sunset before rising again at midnight in this data. Figure 2 displays this survival probability graphed against time of day for 957 fully buried victims sampled over 18 hours and 22 hours for this dataset sample of 957 victims.