Facts about avalanches
Fact: mountain slopes between 20° and 60° + snow = avalanche.
- The most frequent and devastating avalanches occur on slopes of between 30° and 45°.
- Most (80–90%) avalanches occur during or immediately after a heavy fall of new snow; a new fall of snow is the most common ‘trigger’ for an avalanche.
- The majority of avalanches are surface slides involving only the upper layer of snow cover, but less common airborne avalanches also occur.
- The freeze–thaw cycle and the surface-hardening effect of the
wind give rise to crusty surfaces, providing potential sliding surfaces
for subsequent snow layers – either fresh snow or windblown snow ‘slab’.
- Large numbers of climbers and walkers. In winter, the Cairngorms National Park is far more accessible, even than Ben Nevis. In some corries there may be 400–500 people going to climb in a single day. Each person can be a potential trigger for an avalanche.
- The topography of the corries, particularly Coire an Lochain, and their ability to catch snow.
- The position of the headwall of Coire Cas above the ski slopes.
The snow is monitored throughout the ski season. Preventative blasting
is carried out to avoid any serious hazard for skiers.