Wind erodes snow from the windward (upwind) side of obstacles, such as a ridge, and deposits the same snow on the leeward (downwind) terrain. Wind can turn very safe snow into very dangerous snow in a matter of minutes. Wind is usually the most important weather factor in avalanche accidents.
What type of winds cause avalanches?
Average wind speeds between 20 and 60 mph transport and deposit snow of almost any density onto the upper reaches of avalanche starting zones. Average speeds between 30 and 40 mph have the greatest potential to build dangerous slabs in these areas. Remember that new snow is not needed to form an avalanche.
What is a wind slab avalanche?
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard.
What can happen during an avalanche?
During an avalanche, a mass of snow, rock, ice, soil, and other material slides swiftly down a mountainside. Avalanches of rocks or soil are often called landslides. Snowslides, the most common kind of avalanche, can sweep downhill faster than the fastest skier. Avalanches occur as layers in a snowpack slide off.
How do you spot Windslab?
Look for convex pillows of wind-drifted snow on the lee side of ridges and other terrain features. The Wind Slab may have a chalky look and feel. Wind Slabs can be very hard, and may present a hollow drum like sound as you traverse across slope.
What does wind do to snow?
As the wind bounces the eroded snow across the snow surface, it grinds up the snow into small, dense particles. By the time they finally come to a rest on lee of an obstacle–where the wind slows down–they pack into a heavy, dense layer of snow that can easily overload any buried weak layer.
What type of hazard is avalanche?
An avalanche is defined in Colorado state statutes as a “geologic hazard.” Snow avalanches occur in the high mountains of Colorado seasonally as the result of heavy snow accumulations on steep slopes.
What are the 7 causes of avalanches?
7 Major casues
- Snowstorm and Wind Direction: Heavy snowstorms are more likely to cause Avalanches.
- Heavy snowfall: Heavy snowfall is the first, since it deposits snow in unstable areas and puts pressure on the snow-pack.
- Human Activity:
- Vibration or Movement:
- Layers of Snow:
- Steep Slopes:
- Warm Temperature:
How do Windslabs form?
A cohesive layer of snow formed when wind deposits snow onto leeward terrain. Wind slabs are often smooth and rounded and sometimes sound hollow.
What is wind loading in Avalanche?
Wind erodes snow from the windward (upwind) side of obstacles, such as a ridge, and deposits the same snow on the leeward (downwind) terrain. Wind loading is a common denominator in most avalanche accidents.
What happens when an avalanche hits a house?
A fractured mass of snow may flow down a slope or become airborne. As a large avalanche speeds down a mountainside, it may compress the air below it, producing a powerful wind that can blow a house apart, breaking windows, splintering doors, and tearing off the roof.
How can we reduce the risk of an avalanche?
This can take the following forms: wind fences and wind baffles alter wind-deposited snow areas and can reduce avalanche frequency, volume and runout Options (a) through (c) require that the design avalanche velocity, impact pressure and flowing height be calculated in advance.
How do you know if a slope is prone to avalanche?
An old avalanche hunter’s adage: If you have developed a good eye for slope steepness and the effects of wind, you can avoid about 90 percent of all avalanches. • Looks Like: has a sandblasted, scoured, scalloped, roughed-up look. • Feels Like: often hard snow and difficult to negotiate on skis, snowboard or snowmobile.
