Avalanches can be triggered by wind, rain, warming temperatures, snow and earthquakes. They can also be triggered by skiers, snowmobiles, hikers, vibrations from machinery or construction. Avalanches Thousands of avalanches occur in Canada each year. Avalanche facts Avalanche safety What to do: During an avalanche Avalanche facts An avalanche occurs when a layer of snow collapses and slides downhill. Avalanches are caused by four factors: a steep slope, snow cover, a weak layer in the snow cover and a trigger.
Roads and railway tracks may be rerouted to reduce risks. The layer may fail due to the force of gravity, the weight of new snow on top of it, or forces from a skier or snowmachine on it. An avalanche occurs when the forces due to the previous instances become greater than the mechanical strength of the snowpack. There are two distinct types of avalanches: loose avalanches and slab avalanches. In spite of what movies and cartoons depict, the trigger is almost never a loud noise.
In most fatal avalanches, people create the trigger. Once they begin, they have three segments:. When the snow stops, it compacts and sets up like concrete. This is what makes avalanches so dangerous to skiers, hikers and snowmobilers -- they generally cannot dig themselves out and must wait for rescue.
According to the Colorado Avalanche Information Center , most avalanche victims are men in their twenties.
The majority are also experienced in back country sports. Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. 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. A single skier can cause enough vibrations to set off a slide.
Currently, scientists are not able to predict with certainty when and where avalanches will happen. However, they can estimate hazard levels by checking on the snowpack, temperature, and wind conditions. Many ski areas employ avalanche control teams to lessen the danger by starting slides before skiers head for the slopes. At some ski areas, patrols use explosive s to set off avalanches.
0コメント