Live the Dream: Low Down on the Snow Down

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Windslab avalanches

Freeriding can be a risky business. Every year, avalanches kill many freeriders. However, it is a mistake to think that the majority of these skiers and boarders are victims of huge, landscape crushing waves of snow. More often it is the smaller and more prevalent windslab avalanches that brutally surprise freeriders. The sad thing is, the presence of windslab or slab avalanches are relatively easy to predict, if only freeriders are aware of what to look for.

Wind is a key indicator to how likely an avalanche is to occur. If there is no wind, snow is distributed evenly. If there is even a moderate wind, snow is deposited in sheltered areas referred to as lee slopes. The greater the wind and the snowfall, the more dangerous these snow deposits become. Unfortunately, these are not the only conditions that allow an avalanche to occur. Where a ski area is subjected to long periods of sun and high winds, large amounts of snow can also be deposited on the lee slopes.

On these lee slopes the wind packs the snow together in a cohesive mass. The situation becomes especially dangerous when the snow fails to bond with the slope. The lack of bond or ‘weak layer’ can exist within the snow pack for a long period of time and may stay dormant long after snow has stopped falling.

Worryingly, windslab avalanches occur most frequently on slopes of between 28 to 45 degrees, the ideal inclination for skiing and boarding. Slab avalanches require very little disturbance to occur. Often the weight of one rider will be enough. Although less frequent, on very steep slopes it takes even less to trigger an avalanche, in some cases all that is required are adverse weather conditions such as a storm or rapid rise in temperature to create a potential killer.

As a winslab avalanche begins, the whole slab moves at the same time breaking up. The deeper the snow, the more dangerous the avalanche is. However, freeriders should be aware that a relatively shallow avalanche could be fatal.

Powder avalanches

This is a type of avalanche that could level a city block but fortunately it is very rare. Powder avalanches occur after heavy snowfall and begin on slopes of over 45 degrees. Ironically, powder avalanches may start off small but build up to colossal proportions as they meet other small unstable areas of snow. As this occurs repeatedly, an avalanche will quickly become unstoppable. If they travel over a long distance on a steep slope the avalanche can become airborne and attain speeds of up to 250mph. At the front of the avalanche an awesome vortex will form that can uproot large trees and small buildings. The result: Total destruction.

Wet snow avalanches

During periods of warm weather, water from melting surface snow can permeate through the snowpack to a weak layer. As the layer becomes more saturated it gains weight and cannot support itself. If the snow is on a smooth grassy slope there is little friction and a large-scale ‘full depth’ avalanche may occur. If you get caught in such an avalanche you have practically no chance of survival. The snow is heavy and devoid of air spaces. It clentches its victim in a vice-like grip. As it stops moving the snow cements and becomes almost impenetrable. In this scenario, south facing slopes and hot days in spring are the most dangerous places a freerider could be.

Note: Even though there is a science to a slide, predicting avalanches can be extremely difficult because you simply don't know what's beneath the snow. A slope can be made unstable from weak layers metres under the surface.

If you have any doubts about the safety of a slope do not ride it. No run is worth dying for!

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