Loose Snow Avalanches

A loose snow avalanche is an avalanche that releases from a single point and spreads downwards in a cone shape.

The snow which first started moving at the top of the slope gradually picks up more and more snow on its way down, and the avalanche spreads out and becomes gradually bigger.

This kind of avalanche occurs in snow where the bonds between the snow crystals are weak. Unbound dry snow and wet snow avalanches are the most common snow types which can be susceptible to loose snow avalanches. These avalanches usually carry less snow and travel slower than slab avalanches, and are therefore less dangerous. With that said, a loose snow avalanche can still have fatal consequences if it carries you into a terrain trap.

Loose Dry Avalanche

Loose dry avalanches are the release of dry, unconsolidated snow such as newly fallen snow or old surface snow that has faceted. They occur on very steep slopes, usually 35 degrees or steeper. They can also be triggered on lower-angle terrain, but it often results in very small slides that don’t run very far. Loose dry avalanches are associated with new snowfall or extended periods of clear weather. Most loose dry avalanche problems are non-persistent and usually stabilize in hours or days depending on the temperature.

Loose Wet Avalanche

Loose wet avalanches are the release of wet unconsolidated snow, such as new snow or old surface snow that is warming up. As the water content in the snow increases, the snow becomes unconsolidated. Most loose wet avalanches also need a very steep slope to trigger, but they can run further than loose dry avalanches. These avalanches can also run long even when the slope decreases, expecially in cases where they contains large amounts of snow. This type of avalanche generally moves slower, but due to their higher weight they can it result in damages to trees and infrastructure if large enough. Loose wet avalanches are for the most part only a problem late winter or early spring, but it’s usually only problematic for a period of hours at a time, at the warmest point in the day.

Release Zone

Loose snow avalanches are usually triggered during or right after intense weather events such as high snowfall, direct sunlight, or rain. The bindings between the snow crystals are weakened and if it's steep enough the avalanche will release. Most loose snow avalanches are triggered naturally, but they can also be triggered by humans. Fortunately, the avalanche will trigger beneath the person and he/she is normally not taken by it.

Other Avalanche Types

Slab Avalanches

A slab avalanche is an avalanche that loosens as a large, cohesive area of snow of snow and slides downwards.

Find an Avalanche Course

This information is meant to be an introduction to avalanche safety and a knowledge base for backcountry travelers.

But reading it cannot replace real experience in reading conditions and making decisions in the field. We strongly recommend that all backcountry travelers take instructor-led avalanche courses to get hands-on experience in wild snowpacks.