Try checking out some of these links. Lots of info about avalanches! The Avalanche Zone CyberSpace Avalanche Center (CSAC Avalanche Awareness: Information About Avalanches and Avalanche Safety...
not much actually happens to the physical EARTH when an avalanche occurs, but if you mean the environment, it can knock down trees, boulders, and other various movable objects in the vicinity. it,...
Avalanches often happen when loose packed snow becomes too heavy for snow lower down a slope to support it. When the snow becomes too heavy, it creates an avalanche.