1) Dry slab avalanches: Most fatalities occur in dry slab avalanches. These types quickly fracture over wide areas with the victim often caught in the middle. Dry slab avalanches can even be triggered from FLAT TERRAIN at near the bottom of the slope.
Fractures can propagate through the snow at speeds of 50-200 mph. People can sometimes escape but most do not.
When climbing snowmobilers frequently do not have the ability or momemtum to get off the moving slab. Occasionally riders can escape the slab when descending and near the bottom.
See Anatomy of a Slab Avalanche below...