The Trigger and Angle snow to slip off. his means something A trigger is needed for the slab layer of causes the slab to slide off the second thinlayer of ice, This is the second cause of an avalanche The pressure from the weight of a skier can easily cause the top slab layer to break off. Then an avalanche starts The third cause of an avalanche relates to slope angle Most avalanches occur on slopes that have an angle of 25 to 60 degrees. If the slope is greater than 60 degrees, the snow will constantly slide is off. never allowing avalanche conditions to form According to statistics, slab avalanches account for 90 percent of all ski fatalities. Since it is very difficult to know how much stress there is on snow slopes, most ski resorts have strict rules about skiing out of bounds,