avalanches

An avalanche is a rapid flow of snow down a slope, driven by gravity. They occur in mountainous regions where snow accumulates on inclined terrain, especially in winter and spring. Avalanches can release along a distinct fracture plane or from progressively failing layers within the snowpack, and they may travel tens to hundreds of meters or more and sometimes transform into a wet flow after snowmelt.

There are several types. Slab avalanches involve a cohesive layer of snow sliding as a unit atop a weaker layer. Loose-snow avalanches start at a point and entrain more snow as they descend. Wet avalanches form when the snowpack becomes saturated with meltwater and tend to move more slowly but with greater mass; dry avalanches are driven by dry, powdery snow. Mixed forms also occur.

Triggers and conditions: A fragile snowpack can fail under added load from snowfall, wind deposition, or warming. Human activity, additional snowfall, thawing, or rain on snow can initiate releases. Slope angle matters: most avalanches begin on slopes of roughly 30 to 45 degrees, and terrain features such as gullies or convexities influence the path and size of the flow.

Assessment and safety: Forecasts and observations help identify unstable conditions. Indicators include persistent cracking, hollow sounds, recent avalanche activity, and rapid warming. In backcountry settings, travelers use safety gear, travel with companions, and plan routes to minimize exposure to at-risk slopes.

Impact and mitigation: Avalanches pose risks to people, vehicles, and infrastructure in mountainous areas. Mitigation measures include weather and stability assessments, controlled releases in managed zones, land-use planning, education, and rescue readiness.