What is a slip face of a dune?

The slip face of a dune is the steep, leeward side that forms as wind-blown sand accumulates on the windward side, creating a slope that eventually becomes unstable. As sand grains are transported over the crest by the wind, they tumble down the slip face, which can have a more gradual incline compared to the steep angle of the windward side. This process continues as the dune migrates over time, reshaping its structure. The angle of the slip face is typically around 30 to 34 degrees, which is known as the angle of repose for sand.