Tuesday, December 29, 2009 9:51:35 AM
NASA’s Earth Observatory has now published an image showing another peculiar dune form. The image is from the Ténéré Desert in Niger, and Linear dunes are also visible in the picture for comparison.
Two major types of dunes are visible in the image. Large, roughly north-south oriented transverse dunes fill the image frame. This type of dune tends to form at roughly right angles to the dominant, northeasterly winds. The dune crests are marked in this image by darker, steeper sand accumulations that cast shadows. The lighter-toned zones between are lower, interdune “flats.” The large dunes appear to be highly symmetrical with regard to their crests. This pattern suggests that the crest sediments are coarser, preventing the formation of a steeper slip face on the downwind side of the dune by wind-driven motion of similarly sized sand grains.
This particular form of transverse dune is known as a zibar, and it is thought to form by winnowing of smaller sand grains by the wind, which leaves the coarser grains to form dune crests. A second set of thin linear dunes oriented at roughly right angles to the zibar dunes appears to be formed on the larger landforms and is therefore a younger landscape feature. These dunes appear to be forming from finer grains in the same wind field as the larger zibars.
The linear dunes in the Ténéré Desert show up more clearly in the Google Map below. (The area with zibar dunes starts in the lower right corner of the image)
(Red marker at centre of map at 17.583 N, 10.917 E)
PS. See more desert dunes as seen from space here: