Snow Cover

Snow Cover
    In order to better understand Avalanches, it makes sense to first learn about what avalanches are compose of, snow.  Snow forms when atmospheric conditions cause water vapor to condense.  However, it is obvious that all snow doesn't have the same structure.  (Some examples can be seen below) 

1) Simple sectored plate; 2) Dendritic sectored plate; 3) Fern-like stellar dendrite

1) Hollow column, or sheath-like crystal; 2) Needle crystal

    The density of fresh snowfall is dependent on both the kind of snow crystal and the air temperature.  In cold, calm conditions the snowfall is the lightest.  While in warmer climates, where graupel and needle crystals fall, the snowfall is the densest.  The diagram below illustrates which structures are formed at different temperatures.

  When looking at a cross section of snowfall it is often evident what weather conditions formed the cross section.  This is due to the different densities and structures of the snow layers.  The bonds between snow layers are large factor in avalanches.  If there is a weak bond between layers, the top layer can easily slide off the bottom layer.  When this happens it is called a slab avalanche.  Other layering characteristic will create other avalanches and hazards, such as ice avalanches and cornices.

Slab Avalanches
Cornices & Ice
Slope Stability

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