Key takeaways
- An avalanche is a mass of snow sliding down a slope; slab avalanches cause most fatalities.
- They need a slab, a weak layer, a steep enough slope (about 30–45°), and a trigger — often a person's weight.
- Manage the risk with avalanche education, the daily forecast, and rescue gear (beacon, shovel, probe).
- Most avalanche accidents are triggered by the victim or someone in their party.
This is general educational information, not avalanche training. Take a certified avalanche course (such as AIARE) and check your local forecast before entering avalanche terrain.
How avalanches form
Most dangerous avalanches happen when a cohesive layer of snow rests on a weaker layer within the snowpack, and that weak layer fails. The four ingredients are a slab, a weak layer beneath it, a slope steep enough to slide (commonly 30–45°), and a trigger — frequently the weight of a skier or rider. New snow, wind-deposited snow, rapid warming, and rain all stress the snowpack and raise the danger.
Types of avalanche
- Slab avalanche — a cohesive layer releases at once along a fracture line; responsible for most fatalities.
- Loose-snow avalanche (sluff) — starts at a point and fans out; usually smaller.
- Wet avalanche — saturated, heavy snow released by melt or rain.
Before a backcountry day, riders read the regional avalanche forecast for the day’s avalanche problem and danger rating, then pick terrain that matches — for example, sticking to slopes under 30° when a persistent slab problem is rated Considerable.
Staying safe
Safety comes from training and judgement, not gear alone. Carry an avalanche beacon, shovel, and probe and practise avalanche rescue; check the forecast; travel one person at a time across suspect slopes; and keep a wide margin when a persistent weak layer is in the snowpack. Most victims trigger the slide that catches them.
The bottom line
Avalanches are the defining hazard of winter backcountry travel, and the deadly ones are usually slab releases triggered by the victims themselves. The risk is managed — never eliminated — through education, the avalanche forecast, rescue gear, and disciplined terrain choices. Take a certified course before venturing into avalanche terrain.
Frequently asked questions
What causes an avalanche?
Most dangerous avalanches occur when a cohesive slab of snow sits over a weaker buried layer and that layer fails — often under the weight of a person. Key ingredients are a slab, a weak layer, a steep enough slope, and a trigger; new snow, wind loading, rapid warming, and rain all raise the danger.
What slope angle is most dangerous for avalanches?
Most slab avalanches release on slopes between about 30 and 45 degrees, with the sweet spot near the upper-30s. Lower-angle slopes rarely slide, but can still be hit by avalanches running down from steeper terrain above.
How do you stay safe in avalanche terrain?
Get formal avalanche training, check the local avalanche forecast before every trip, carry and know how to use a beacon, shovel, and probe (an airbag is recommended), travel one-at-a-time on suspect slopes, and choose terrain conservatively. This is an overview, not a substitute for a course.
Sources
- Avalanche basics — Avalanche.org
- Avalanche education — American Institute for Avalanche Research and Education
- Avalanche encyclopedia — American Avalanche Association