What is an avalanche?
An avalanche is a high-velocity flow of snow down a mountainside. Avalanches are among the biggest dangers in the mountains for both life and property. Many factors contribute to avalanches. Loose snow avalanches occur when the weight of the snowpack exceeds the shear strength within it, and are most common on steeper terrain. Slab avalanches account for around 90% of avalanche-related fatalities, and occur when there is a strong, stiff layer of snow known as a slab. These are usually formed when snow is deposited by the wind on a lee slop. The third starting type is a slush avalanche which occurs when the snowpack becomes saturated by water. These tend to also start and spread out from a point. As avalanches move down the slope they may entrain snow from the snowpack and grow in size. The snow may mix with air and form a powder cloud. An avalanche with a powder cloud is known as a powder snow avalanche. The powder cloud is a turbulent suspension of snow particles that flows as a gravity current. Powder snow avalanches are the largest avalanches and exceed 300km/h and 10,000,000 tons of snow; they can flow for a long distance along flat valley bottoms and even up hill for short distances.
Safety in avalanches.
- Group management- Group management is the practice of reducing the risk of having a member of a group, or a whole group involved in an avalanche. Minimize the number of people on the slope, and maintain separation. Ideally one person should pass over the slope into an area protected from the avalanche hazard before the next one leaves protective cover. Route selection should also consider what dangers lie above and below the route, and the consequences of an unexpected avalanche. Stop or camp only in safe locations. Wear warm gear to delay hypothermia if buried.
- Group size- Group size must balance the hazard of not having enough people to effectively carry out a rescue with the risk of having too many members of the group to safely manage the risks. It is generally recommended not to travel alone. There will be no-one to witness your burial and start the rescue.
- Leadership- Leader ship in avalanches teerain requires well defind decision making protocols, which are being taught in a growing number of courses provided by national avalanche resource centers in Europe and North America. Fundamental to leadership in avalanche terrain is an honest attempt at assessing ones blind spots. There is a growing body of research into the psychological behaviors and group dynamics that lead to avalanche involvement.
Myths about avalanches.
Myth:Avalanches can be triggered by shouting-Avalanches cannot be triggered by sound as the forces exerted by the pressures in sound waves are far too low. The very large shockwaves produced by explosions can trigger avalanches, however, if they are close enough to the surface.
Myth: There is an air blast in front of an avalanche-Avalanches travel much slower than the speed of sound and therefore there are no shock waves. The pressure in front of an avalanche is exactly the same as in front of any object moving at a similar speed and increases smoothly as the avalanche approaches.