Frosted gullies of Mars
In frosty conditions, sand on Martian dunes can start to flow.
Gullies on Martian sand dunes, like these in Matara Crater, have been very active, with many flows in the last ten years. The flows typically occur when seasonal frost is present.
In this image from NASA’s Mars Reconnaissance Orbiter we see frost in and around two gullies, which have both been active before.
There are no fresh flows so far this year, but HiRISE will keep watching.
The map is projected here at a scale of 50 centimeters per pixel. North is up.