What causes slab avalanches to fracture?
Snow is a lot like people. It doesn’t like rapid change. (Raise taxes slowly enough and no one notices.) Dry slab avalanches occur when the weak layer beneath the slab fractures, usually because too much additional weight has been added too quickly, which overloads the buried weak layer. Snow is very sensitive to the rate at which it is loaded or stressed. Two feet of snow added over two weeks is not a problem. Two feet of snow in two days is a much bigger problem. Two feet of snow in two hours is a huge problem. (Wind can easily deposit two feet of snow in two hours.) Then, finally the weight of a person can add a tremendous stress to a buried weak layer, not in two hours, but in two tenths of a second-a very rapid change. That is why in 90 percent of avalanche accidents, the avalanche is triggered by the victim (or someone in the victim’s party). Wet slab avalanches occur for the opposite reason. Percolating water dissolves the bonds between the snow grains, which decrease the streng
