The most common landforms in the image are star dunes and barchan (or crescent) dunes. Small linear dunes appear at top left. Star dunes are formed when sand is transported from variable wind directions, whereas barchan dunes form in a single dominant wind regime. The superimposition of two dune types suggests that wind regimes have changed through time. The active nature of this portion of the Erg is well illustrated by this image--smaller dunes form and migrate along the flanks of the larger dunes and sand ridges. Occasional precipitation fills basins formed by the dunes; as the water evaporates, salt deposits are left behind which appear as bluish-white areas.