Angle of Repose
The lowest slope angle at which a granular material will begin to slide, or the steepest incline at which it will not slide.
One of the most basic examples is a pile of sand. If sand is poured slowly onto a pile it will form at a specific angle to the hozontal surface beneath the pile, which is the angle of repose. Any additional grains added to the pile will slide down its surface, perhaps causing some others to do the same.
Another example is a sandy embankment along a stream. If this is at the angle of repose, which it often is, grains on the surface will slide down very easily and sometimes spontaneously.
Snow can be a granular material, but as it sits on a slope it often is not. The grains are often bonded together into a slab.
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