4. Dunes of Simpson Desert, Australia
The first crossing of Queensland's Simpson Desert was accomplished as recently as 1939, which helps to indicate just how remote this region is. The linear streaks in the desert terrain are sand dunes, 20–30 meters (66–99 feet) high, shaped and formed by the prevailing winds. Wind direction is from bottom to top of the photograph. The light-toned areas are salt-crusted playa lake beds, probably formed by deflation, scouring of the surface by the wind, and removal of eroded material.
The origin of the very long thin dunes is not resolved; the most likely hypothesis is that they are the attenuated arms of parabolic dunes, whose curved central portion is not preserved. For the most part, the dunes are only semiactive; the dune field formed and was most active during the glacial period.
During the rainy season of the southern summer, the lakes pictured here fill and vegetation flourishes around the banks. This picture was taken in September, before the rains, and shows the lakes virtually dried out, with only traces of moisture showing blue/gray in the still damp centers while a white salty residue is left around the dried-out lake margin.
STS-41D, August-September 1984. Picture #14-42-107.