The steepness or incline of a piece of terrain
Slope angle is a key factor for dictating whether or not the terrain can produce an avalanche. Most slab avalanches initiate on slopes where the steepest slope angle is between 30° and 50° (about the steepness of a black or double black diamond run at a ski hill) and subsequently run into lower angled terrain. Avalanches initiating on slopes less than 30 degrees are rare because the incline is so flat. Slopes steeper than 50 degrees are so steep that small loose avalanches run frequently so they only rarely develop the structure for larger slab avalanches.