Issaouane Erg, Algeria

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.