Slab Avalanches

Snow Cover
    The two main avalanches are loose snow and slab avalanches.  These two types of avalanches are distinguished by the snow condition at the origin.  However, sometimes classifications must be modified on long avalanches, due to the fact that snow conditions vary throughout the avalanche.  All avalanches have a great potential energy, that can be determined by their height and the force of an avalanche is simply F= ma.  This means that if a small avalanche contains 1000 kg of snow, it has a force of 9810 Newtons.

    Loose snow avalanches usually start at a point or small area and expand as they move.  They are a result of snow that has been deposited at a steeper angle then the snow’s natural angle of repose.  The most dangerous loose snow avalanches are made of wet snow.  This is because the wet snow is denser and has a greater destructive force even though the velocities may be low.  The diagram shows the differences between loose snow and slab avalanches.

The ABC of Avalanche Safety

    Slab avalanches are the most dangerous type of avalanche.  They are the largest source of winter hazards, and most are triggered by the victims.  Slab avalanches form in almost all types of snow.  Wind is an important factor to these avalanches, because it causes and unstable slab.  However, wind alone will not cause a slab avalanche.

    Gravity and the strength of the bonds between snow layers are important in slab avalanches.  This is because gravity is the force which is pulling the slab down the mountain.  When the force of gravity is greater than the bond between layers the gravity causes the top layer to separate and slide down the mountain.

    The diagram below gives a good idea as to how a slab avalanche moves.  It is easy to see how after the avalanche is triggered there is start zone, which moves down the "track" and finally ends in a debris toe.  As the avalanche moves down the mountain kinetic energy increases while the potential energy decreases.

Slab Avalanches
Cornices & Ice
Slope Stability

Created by Sarah Schlichting for Physics 212
Last modified 04-04-03