An avalanche, sometimes called a snowslide, is the rapid flow of snow, ice and/or rock down a slope or mountain. They can be triggered by natural forces such as precipitation, earthquakes or the weakening of snowpack (layers of slow that accumulate in areas of high elevation and cold temperatures). They can also be caused by human activity when someone walks or rides over a weak area of snow. Slab avalanches—when a large slab of stronger ice or snow dislodges from on top of a weaker snow layer—are the most dangerous. Avalanches can obstruct everything in their path, destroy entire buildings and lead to serious injury and death.

Do you know how to prepare for an avalanche?

Check the weather conditions before going out onto a mountain and never go out alone. Tell someone your route and the approximate time you intend to return. If you are a skier, snowboarder or snowshoer, get yourself an avalanche victim detector and learn how to use it. Wear warm clothes and bring a survival blanket with you.

You should always stay up to date with and follow the advice of local authorities before heading out onto a mountain. It is safer to stick to planned snow tracks, though these are still not an absolute guarantee of safety. 

If you witness an avalanche with people affected, follow them with your eyes and note the point where you last saw them. If possible, ask someone to be a lookout while you alert emergency services. Do not approach the site of the avalanche. If you are caught in an avalanche, try to escape laterally i.e. horizontally across the slope or hold into an object like a tree as an anchor. Get rid of any equipment and cover your mouth with your hand or a scarf. If you are buried, try to push yourself upwards and make an air pocket in front of your face. Remain calm while waiting to be rescued.

Do's and dont's

Check weather warnings and conditions
Wear warm clothing
Tell people where you are going and when you expect to return
Never go out on a mountain alone
Track where affected people are with your eyes and alert authorities
If you get buried, keep your mouth shut and teeth clenches
Try to escape horizontally across the mountain, not by going down

Watch: how to prepare in case of an avalanche