Barchans are crescent-shaped sand dunes whose two horns face in the direction of the fluid flow. They appear in different environments, such as inside water pipes or on river beds, where they take the form of ten-centimeter ripples, and deserts, where they can exceed 100 meters, and the surface of Mars, where they can be a kilometer in length or more. If their size varies greatly, so does the time they take to form and interact. The orders of magnitude range from a minute for small barchans in water to a year for large desert formations and a millennium for the giants on Mars.
Source:
https://phys.org/news/2020-12-dune-dynamics-scientists-topography-mars.html