On any slope, the snow is piled up and supported by a snow-pack. It keeps the snow from tumbling down all the time. Avalanches occur when the snow-pack starts to weaken and allows the buildup of snow to be released. Small avalanches are generally made up of ice, snow and air. The larger ones comprise of rocks, trees, debris and even mud that is resting on the lower slopes. Contrary to belief, these snow slides are not random events that occur without any warning signs. Winter season is when they are most common, often brought on after a large storm in the area. Rainfall and sleet also tend to be responsible for avalanches in the summer and monsoon season.