The Issaouane Erg (sand sea) is located in eastern Algeria between the Tinrhert Plateau to the north and the Fadnoun Plateau to the south. Ergs are vast areas of moving sand with little to no vegetation cover. Considered to be part of the Sahara Desert, the Issaouane Erg covers an area of approximately 38,000 km2. These complex dunes form the active southwestern border of the sand sea.
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.
Astronaut photograph ISS010-E-13539
was acquired January 16, 2005 with a Kodak 760C digital camera with an 800 mm lens, and is provided by the ISS Crew Earth Observations experiment and the Image Science & Analysis Group, Johnson Space Center. The International Space Station Program supports the laboratory to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth.
he Issaouane Erg (sand sea) is located in eastern Algeria between the Tinrhert Plateau to the north and the Fadnoun Plateau to the south. Considered to be part of the Sahara Desert, the Issaouane Erg covers an area of approximately 38,000 km2. These complex dunes form the active southwestern border of the sand sea.
One of the main reasons that rainless regions like the Sahara Desert are interesting from the perspective of landscape science is that the work of flowing water—mainly streams and rivers—becomes less important than the work of wind. Over millennia, if enough sand is available, winds can generate dunes of enormous size, arranged in regular patterns. Long, linear dunes stretch generally north to south across much of northeast Algeria, covering a vast tract (~140,000 square kilometers) of the Sahara Desert known as the Erg Oriental. Erg means “dune sea” in Arabic, and the term has been adopted by modern geologists. Spanning this image from a point on the southwest margin of the erg (image center point: 28.9°N 4.8°W) are a series of 2-kilometer-wide linear dunes, comprised of red sand. The dune chains are more than 100 meters high. The “streets” between the dunes are grayer areas free of sand.