Sand avalanches on Mars. Satellite image of the Meroe Patera region on the surface of Mars, showing a region where sand dunes are missing downwind (left) of a crater (near centre) because sand has fallen into the crater and is trapped. Comparing this with older images revealed that several major sand flows slumped down into the crater (upper left), leaving small ridges (levees) along their path and rounded piles of sand at the end. It is likely that these slumps were dry flows, similar to, but much larger than, the avalanches commonly seen on sand dunes. Given their size it is possible that they were a result of a Mars-quake (earthquake) or an unusually strong wind. Imaged by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars