What Is an Avalanche?

An avalanche occurs when built-up snow is dislodged and slides suddenly down a hill or mountain. They can be small in size or very large, depending on many factors. Fatalities from avalanches are not uncommon, as skiers, backpackers and other individuals that use mountainsides for recreation can become victims. Here are some more facts about avalanches.

Types

The most frequent type of avalanche is called a loose snow avalanche, one in which the snow layer on top of other snow comes loose and cascades down a mountain. A slab avalanche happens when the entire snow pack breaks loose and comes down. Isothermal avalanches are rarer and can start when the snow becomes full of water. The powder snow avalanche is one in which air mixes in with the snow and forms a cloud that precedes the avalanche. This type will come down a mountain the quickest and has the ability to go the furthest of any avalanche.

Geography

Avalanches take place in mountainous terrain where there is the possibility of heavy snows. The United States experiences many avalanches each year in its northern states. Canada frequently has avalanches, as do European countries such as France, Austria and Switzerland. Mountains with very steep slopes do not have avalanches since the snow cannot accumulate there. The slopes most likely to have an avalanche are those with 25- to 60-degree angles.

Considerations

There are many factors to consider when talking about the causes of an avalanche. One is the actual structure of the snow layers, while another, of course, is the weather. Temperature, rain or snowfall, winds and heating by the sun are all parts of the formula of an avalanche. The type of terrain is also important.

History

Avalanches have claimed thousands of lives over the years. One of the worst of recent times was in Peru, where over 18,000 died when an earthquake caused an avalanche in the western Andes. A 1910 avalanche in the Cascade Mountains in Washington State is the worst in United States history. Two trains that were snowbound were swept 150 feet down a mountainside, killing almost 100 people. In World War I, an estimated 50,000 troops were killed in avalanches in the Alps.

Prevention/Solution

Explosives are primarily used to control avalanches, especially at ski resorts. Snow packs that pose a danger are rigged with explosives and set off before they can grow to a size that would trigger an avalanche. Snow barriers made of wood, concrete and steel can be employed to lessen the damage from avalanches. Barriers that deflect the power of an avalanche are erected over roadways and railways, designed to send the snow in another direction.