slip face

The gradual, inexorable movement of dunes occurs when winds from one direction blow unceasingly upon mounds of uniform sand. Individual grains move up along the windward side of the dune, eventually reaching its crest. There they cascade down its steeper, leeward side, known as the slip face, before resting at an angle of repose at its foot. This process causes the dune itself to advance, as many as several dozen feet per year, often covering roads, farms, and most other objects in its path.

Lan Samantha Chang