ISS022-E-5258

Browse image
Resolutions offered for this image:
1000 x 664 pixels 540 x 359 pixels 720 x 480 pixels 4288 x 2929 pixels 640 x 437 pixels
Cloud masks available for this image:

Spacecraft nadir point: 15.7° N, 9.5° E

Photo center point: 17.2° N, 11.5° E

Nadir to Photo Center: Northeast

Spacecraft Altitude: 181 nautical miles (335km)
Click for Google map
Width Height Annotated Cropped Purpose Links
1000 pixels 664 pixels No Yes Earth From Space collection Download Image
540 pixels 359 pixels Yes Yes Earth From Space collection Download Image
720 pixels 480 pixels Yes Yes NASA's Earth Observatory web site Download Image
4288 pixels 2929 pixels No No Download Image
640 pixels 437 pixels No No Download Image
Other options available:
Download Packaged File
Download a Google Earth KML for this Image
View photo footprint information
Image Caption: Sand Dunes in the Tenere Desert, Niger

This detailed astronaut photograph highlights sand dunes in the Fachi-Bilma erg (sand sea) in the central-eastern part of the Tenere Desert. The Tenere occupies much of southeastern Niger and is considered to be part of the larger Sahara Desert, which stretches across northern Africa. Much of the Sahara is comprised of ergs; with an area of approximately 150,000 square kilometers (57,915 square miles), the Fachi-Bilma is one of the larger sand seas.

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.