Dune movement around Aorounga
The Aorounga impact structure in northern Chad is 12.6 kilometres (7.8 miles) in diameter, large enough to display a central peak and more than one concentric ring. This eroded remnant of a crater in Africa's Sahara Desert is estimated to be less than 345 million years old. Astronauts have photographed it several times over the years, most recently in 2009 and in 2011. But it's not the crater itself that caught NASA's eyes this time. It is the sandy landscape around it.
Images of the central Sahara Desert taken from the International Space Station (ISS) often include sand dunes. Two comparative images feature a series of horn-shaped "barchan" dunes clustered in a narrow corridor between lines of dark-toned hills. The horns point in the direction of dune migration; that is, from north-northwest to south-southeast under the influence of the prevailing winds. Thick zones of rippled, light-toned dunes are visible at the bottom of the images, with dry river channels in the centre and upper parts.
The opportunities for comparisons of the landscape are growing with each new year that we send humans and satellites into space. The imagery is quite valuable to remote-sensing scientists. For example, where large masses of sand move across highways or into farm fields, as is common on the edges of deserts, they cause great environmental damage and cost. With comparative imagery, it is now possible to predict when dunes are likely to cause such damage so that mitigation efforts can be put in place.
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Credit: NASA Earth Observatory