An avalanche is a natural process in which snow responds to the pull of gravity. Avalanches occur regularly on mountains around the world, and are harmless, unless someone happens to be in the way. They tend to run down the same pathways every year, and danger zones are usually well known. Avalanches are born from a weakness in the snow.
Snow is a shape-changer, depending on prevailing temperature and weather conditions.
Snow begins life as a fluffy six-armed crystal flake, but while it's laying on the ground, as part of a snowpack, changes occur. During mild weather, water vapors can slide down the arms of a flake and refreeze at its center. If this happens, the individual flakes develop strong bonds and form a solid and cohesive mass. But when it is cold, water vapors can slip to the bottom of the snowpack, forming angular crystals. These crystals tend to weaken the snow and undermine it from below.