Propelled by gravity, snowslides have the power to rip through forests leaving distinctive cuts often mistaken for ski runs. Like the snow crystals that give them birth, slidepaths mark the landscape with an endless variety of shapes and sizes. Some paths thunder with snow many times a winter, others may lurk quietly for centuries.Two types of snow avalanches What makes snow avalanche?
Glacier National Park
1997-0-064 Glacier National Park, BC, April 1980. © Parks Canada, John G Woods.
When snow and slope combine with a hidden weakness beneath the surface, you have set the stage for an avalanche waiting to be triggered.Learn more
Controlled avalanche at Bear Pass, BC. Revelstoke Museum & Archives 5529. © BC Ministry of Transportation and Infrastructure.
There is no exact answer. On a smooth slope 30 cm is enough to create an avalanche.Slope
Yearly snowfall often exceeds 10 m in Rogers Pass. Here men saw and slide huge chunks of the winter’s snow accumulation from the roof of the Glacier House Hotel, circa 1926. © Whyte Museum of the Canadian Rockies V263 / NA – 1360, Byron Harmon.
Avalanches have run down slopes from 10° to nearly 90°. Most recreational avalanche accidents have happened on slopes between 30° and 35°.Weak layer
All in a Day's Work
Chief Avalanche Forecaster V. G. (Fred) Schleiss takes a moment to marvel at the beauty of his workplace high above the Trans-Canada Highway, in the trigger zone of Lanark Slidepath circa 1979, Revelstoke Museum & Archives 5563. © Parks Canada, John G. Woods.
Storms deposit snowfall in layers. The crystals within these layers, as well as on the surface, are always changing. This results in layers of different strengths—some weaker, some stronger.Trigger
Some crystals cling together, others are as loose as sugar. Avalanche professional John Tweedy looks for weak layers in the snow that could provide a sliding surface for an avalanche. Revelstoke Museum & Archives 5331. © BC Ministry of Transportation and Infrastructure.
Falling snow, drifting snow, temperature change, rain, a mountain goat, a skier, a snow machine, an explosion…
Any force that initiates a facture at a weak layer in the snowpack. Avalanche professional Jim Bay, Valhalla Range, BC, 2013. Revelstoke Museum & Archives 5532. © Jim Bay