These gorgeous dunes are likely active, with ripples on their upwind slopes and dark streaks on their downwind slopes forming and changing due to wind-driven sand motion.

This motion will also keep the dune brink (the edge between the two slopes) and bottom edges sharply defined. The dark lines and squiggles on the dune slope are formed by passing dust devils.

ID: ESP_021893_1315
date: 29 March 2011
altitude: 255 km

https://uahirise.org/hipod/ESP_021893_1315
NASA/JPL-Caltech/University of Arizona
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