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Avalanche Type

While there are many different types of avalanche, we can place them into two broad categories; Loose, and Slab.  Each has different characteristics to tell them apart.

Loose Snow/ Point Release Avalanche

A loose snow avalanche is also often called a point release avalanche. As the names suggest, they involve loose, unconsolidated snow which initiates from a point, gradually fanning out as it moves downhill. This often makes for a ‘teardrop’ shape.

The triggered weak layer tends to be the top layer of the snowpack, the surface layer(s). (Loose avalanches start where the stress is applied.)

Below is an example video of typical small loose avalanches:

Slab Avalanche

A slab avalanche involves a cohesive block of snow that fractures within the snowpack. A crack spreads out across the slope leaving a tell tale fracture line called a crown wall. The slab will break up into smaller blocks as it moves downhill.

The triggered weak area (layer) is below the surface layer, within the snowpack. Slab avalanches need a relatively strong layer of snow over a relatively weaker layer. When stress becomes too much for the slab to take, it’s ‘back will break’ starting a slab avalanche in motion. Slab avalanches can break above you, giving you little or no escape. That's why slab avalanches pose the greatest danger - watch these video examples...

(To read more on avalanche danger problems that are used in the Backcountry Advisories CLICK HERE)

 

Avalanche Size

Avalanches range from tiny loose snow sloughs (pronounced sluffs) up to monstrous walls of snow like a tsunami. Generally the bigger they are, the greater the destruction will be.

We rate avalanche size using this scale:

NOTE: Small slides can be enough to cause injury/death if you find yourself in an exposed place like a steep walled gully, ice couloir, or above a cliff. (Terrain traps – more on this later)