Reversing slip faces

Reversing dune on Mars, HiRISE image ESP_050887_2225. Image Credit: NASA/JPL/Univ. of Arizona

A Piece of Mars: This 523×750 m (0.32×0.47 mi) scene shows a large dune. It’s quite colorful for some reason, although it’s partially false-color. What caught my eye is that the slip face on this dune has reversed direction, which is somewhat rare on Mars (but common on Earth). The main sand-moving wind blows from the right, forming a long avalanching slope (you can see long bright lines of grain fall slips at the lower center). But at some point a wind blew from the left, forming a small slip face in the opposite direction. Although many other wind directions have also help to build this dune, those two are the main winds apparent here.