One reason dunes are hard to find in the Viking images is their size; they are so small that they are visible only in the highest-resolution photographs. These dunes are a case in point; in medium resolution they were invisible and the geologic interpretation did not include aeolian landforms. At image resolution sufficient to show objects a few tens of meters across, however, the dunes are more obvious. Here the direction of the wind and deposition of the sand is controlled by the topography. The wind is forced to flow along the valleys where it forms transverse dunes. Note that the dunes remain transverse to the valley even when the valley changes direction.
–38°, Longitude 135°. Viking photograph 442B10, NGF orthographic
version, clear filter.