Avalanches involving people do not happen by accident. Three variables interact to determine whether an avalanche is possible. 1) Terrain: the slope must be steep enough to avalanche 2) Snowpack: the snow must be unstable enough to avalanche 3) Weather: Weather is another important variable. Changing weather can quickly increase instability. People: If people or property were not present we would not have to worry about avalanches. But many of us love to go into the backcountry to ski, snowboard, snowshoe or snowmobile. And our very presence is what often upsets the delicate balance within the snowpack between stress and strength and causes an avalanche.