Ensure you have an experienced group leader. Always stay within view of your group. Avalanches may reach the road without warning. Obey road closures. When the avalanche hazard is high, control work by explosives may be carried out at any time. If an avalanche blocks the highway, remain in your vehicle with seat belts on.
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A snowpack is simply layers of snow that build up in an area, such as the side of a mountain. In winter, repeated snowfalls build a snowpack dozens of meters thick.
The layers vary in thickness and texture. The bonds between the layers of a snowpack may be weak. Melted snow that refreezes may cause a slick coating of ice to form on the surface of a layer. A new snowfall may not stick to this slippery layer, and it may slide off. During spring thaw, melted snow can seep through a snowpack, making the surface of a lower layer slippery. Added weight or vibration can easily send the top layers of a snowpack hurtling downhill.
Sluffs and Slabs There are two main types of snow avalanches—sluffs and slabs. Sluff avalanche s occur when the weak layer of a snowpack is on the top. A sluff is a small slide of dry, powdery snow that moves as a formless mass. Sluffs are much less dangerous than slab avalanches. A slab avalanche occurs when the weak layer lies lower down in a snowpack. This layer is covered with other layers of compress ed snow.
When the avalanche is triggered, the weak layer breaks off, pulling all the layers on top of it down the slope. These layers tumble and fall in a giant block, or slab. Once a slab avalanche starts, the slab shatters into many separate blocks.
These snow blocks break up into ever-smaller pieces. Some of the pieces rise into the air as a moving cloud of icy particles. The cloud races downhill at very high speeds. The thickness and speed of slab avalanches make them a threat to skiers, snowboarders, mountaineers, and hikers.
In the mountains of the western United States, there are about , avalanches each year. Avalanches kill more than people worldwide each year. Most are snowmobilers, skiers, and snowboarders. Avalanche Control Storminess, temperature , wind, the steepness of the slope, terrain , vegetation , and general snowpack conditions are all factors that influence whether an avalanche happens and what type occurs.
Snow avalanches are most likely to occur after a fresh snowfall adds a new layer to a snowpack. If new snow piles up during a storm, the snowpack may become overloaded, setting off a slide. Earthquake s can set off avalanches, but much smaller vibrations can trigger them as well. Cryosphere, 8, 2: Havens, S. Cold Regions Science and Technology, 65, 3: Cryosphere, 5, 2: Bellaire, S. Journal of Glaciology, 55, Pielmeier, C.
Cold Regions Science and Technology, 59, Cold Regions Science and Technology, 47, Cold Regions Science and Technology, 46, 1: Birkeland, K. Annals of Glaciology, Main menu. Main menu Whether or not an avalanche releases at a particular location depends primarily on the structure of the snowpack. Loose-snow avalanche. Image: SLF Archive. Avalanche formation Loose snow avalanches start from a single point and form when snow is not well bonded.
Slab avalanche in the Grialetsch area. Experiments and models The aim of our research is to better understand the processes that take place before, during and after avalanche release. This includes for example: filming a fracture as it propagates inside a weak layer using high-speed cameras; determining the water content of the snowpack from the ground using radar systems; measuring the stratification and variability of individual snow layers using the SnowMicroPen, a high-resolution snow sampler.
Load tests in the cold laboratory. An early warning model framework for snow avalanches When and where are avalanches likely to occur? Seismo-acoustic avalanche detection How can avalanche activity be determined in bad visibility and in remote regions? Snow instability in a changing climate Less snow, less avalanches? Improving avalanche forecasting with snow cover models How would it change your picture of the avalanche danger, if you could look deep into the snowpack at any time and anywhere?
Avalanche terrain maps New maps show avalanche terrain and take into account avalanche release and runout. Model avalanche release A recently developed model describes the principal factors contributing to the release of a slab avalanche. Shear apparatus In the laboratory, researchers are investigating the process which causes snow to fracture. Seismic avalanche detection SLF is working on detecting avalanches with seismic sensors - as is usally done for earthquakes.
Fracture propagation Before a snow slab avalanche releases, a buried weak snowpack layer has to fracture break over a large area. AVAL-1D Avalanche hazard maps are prepared by engineers and land-planners who rely both on practical experience and calculation models to predict avalanche runout distances and flow velocities. Person in charge: Marc Christen. Avalanche bulletin In its avalanche bulletins, the SLF provides information about the current avalanche situation.
Person in charge: Thomas Stucki.
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