Avalanches occur when weak snow breaks off from the slope and moves downward. The characteristic properties of a snowpack that are important in its overall strength and therefore its potential to produce an avalanche are density, temperature, and crystal type (Trabant, D.C. et al).
The strength of a snowpack is strongly related to its density. Snow with high densities tend to be much stronger than lower density snow. Mountainous snow tends to have low density thus adding to the tendency to produce avalanches (Perla, R.I. and Matinelli, 1976).
In areas that have low density snow, snow crystals shape in an important factor in the snowpack's overall strength. Keeping everything else the same, as the size of the snow crystal increases, their strength decreases (Perla, R.I. and Matinelli, 1976). This becomes apparent when looking at their relative lever arm lengths. As the lever arm length increases, a smaller force is required to produce movement. Therefore large snow crystals with long lever arms are likely to shear more quickly than snow crystals with short lever arms.
The effects of temperature on the strength of snow is not currently known (Perla, R.I. and Matinelli, 1976). It is known that if the temperature is highenough to cause melting, the strength of the snowpack decreases,but it does not appear than any sudden significant snow temperature change will affect the stability of a dry snowpack.