THEMIS Image of the Day, February 15, 2019. This VIS image is located in Kaiser Crater and shows several individual dunes. These dunes’ dark tone suggests they are free of dust, hence active.
With continued winds sand dunes will move across the surface. There are two sides to a dune, the low angle slope of the windward face and the high angle slope of the leeward side.
The steep side is called the slip face. Wind blows sand grains up the low angle slope of the dunes which then “fall down” the slip face. In this way the whole dune moves towards the slip face.
The winds blow from the windward to the leeward side of the dunes. In this image the slip faces are on the left side of the dune, so the dunes are slowly moving to the right side of this image.