echo dune

An echo dune is a large dune that forms on the upwind side of a topographic obstruction, such as a scarp or hill massif. It is separated from the obstruction by a rolling eddy of air that keeps a corridor free of sand. These corridors can be important for oases and travel routes within deserts. Echo dunes are among the largest types of dunes, sometimes exceeding 400 meters in height.1

Sand dunes, in general, are accumulations of sand shaped by wind and gravity. They are found in deserts, on beaches, and even on other planets like Mars. The formation and patterns of dunes are influenced by sand composition, wind speed and direction, and topography.1