Actually, I don't know much about this, but I know something about the reason why the windward slope of sand dunes is slow and the leeward slope is steep, so I'll give you a reference ~

The shape of sand dunes is closely related to the direction of prevailing wind. Due to wind erosion, the windward slope is generally gentle. When the airflow containing sand particles passes through the top of the sand dune, it often forms a vortex on the leeward slope, making the leeward slope form a horseshoe-shaped depression. There is less sand deposited in the depression and more sand accumulated on the two wings, so the leeward slope of sand dunes is steep.