Winter brings snowfall in the western mountains and the accumulated layers of the snowpack provides bountiful cold season entertainment. For outdoor enthusiasts, the range of activity spreads from slower moving recreation, such as snowshoeing, to the speed of downhill skiing or snowmobiling. Any of these adventures can end in disaster if attention to the snowpack stability is timed with an unstable accumulation of the snow.
Couple of terms:
Stability. Influenced by how well the different layers of snow adhere to one another and the surface on which they fall.
Shear Strength. The bond and anchorage of snow layers.
Shear Stress. The downslope force of gravity.
In a nutshell of understanding, when the shear stress outweighs shear strength, an unstable mass of snow breaks loose creating a snow avalanche.
Avalanches are a natural phenomenon that from afar can be respected and valuable to watch. Seeing the force and magnitude of even a small side can reveal the destruction and danger to which we should all be aware. Ranging from minor and superficial to significant and deep, the destructive potential for any slide is contingent upon the strength of the individual layers from successful sintering.
Point release snow avalanches have minimal internal organization. Easily distinguished, these type of avalanches start at a point and set additional snow in motion that grows wider the further down slope the slide progresses. Generally shallow with little damage, this is one of the signifiers of more dangerous avalanche conditions seen immediately after freshly fallen snow. In the spring, these are more dangerous avalanches when the snow is wet and heavy.
Slab avalanches occur with less frequency but are more dangerous and destructive and result when a plate of cohesive snow begins to slide as a unit before breaking into smaller pieces further down slope. Natural triggers include new snow, as well as warming temperatures or cornice failure. Artificial triggers can be caused by the passing of people or wildlife.
Understanding the zones of an avalanche path are helpful when planning escape routes on higher risk snow routes. The starting zone is just that, the uppermost part of the avalanche path. The track is the area to which an avalanche travels. The runout zone is the debris field accumulated at the bottom of the slope. Ranging in speed from 50 to 200 kilometers an hour, knowledge and awareness go a long way to remaining safe in the wintery backcountry.