This image is a section of an impact site in the Acidalia Planitia albedo region of Mars.
In several areas, material has been pulled down by gravity and weathering due by wind mainly in the crater walls. This has caused small, observable avalanches and has created channels of material descending down into the crater. Located at the bottom of the image is a section of slightly elevated terrain, possible central uplift from the impact crater. Situated on the central uplift is a well matured dune field. The slopes of the crater walls contain less developed dunes.
A field of barchan-type dunes is located on the up lift at the bottom of the image. Judging by the orientation the dunes, the wind is coming from the southwest. At the base of the uplift there is a field of transverse dunes. They also spread into the valleys of the barchan-type dunes. The crater walls also contain linear ripples and have loose material avalanching down them. These are less developed than the dunes near the southern field. The disruptions may occur in the dune fields as a result of movement of material down the crater wall by avalanching. Combined with the wind, this causes the ripples to be constantly developing and reforming.
Note: this caption was written by William Lucas.Written by: William Lucas/Circe Verba (20 May 2009)
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Image: NASA/JPL/University of Arizona