Slope angle, or incline, is one o f the most significant terrain characteristics that determines whether an avalanche can occur. Slab avalanches most commonly occur on slopes between 25° and 45°, and since slab avalanches tend to be the most deadly, these are the slopes we’re most concerned about. The problem is that these are also the slopes that most backcountry recreationists tend to seek. For slopes less than 25°, the stress on the snowpack tends to greater into the slope than down-slope, which helps to hold the snow in place. For slopes steeper than 45°, the down-slope component of stress due to gravity is so great that the snow has a hard time bonding and cohesive slabs usually don’t form.
It's often difficult to judge slope angles by looking at them, so use a small clinometer or ski poles whenever you're not sure if a slope is steep enough to produce avalanches. Or simply ask yourself: Is the slope flat enough to hold snow, but steep enough to ride?