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| Keywords: Erg Oriental Algeria.jpg en 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 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 North 4 8 West 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 Linear dune chains are usually generated roughly parallel to the dominant winds It also seems to be true that linear dunes are built by stronger winds This detailed astronaut photograph shows that smaller dunes known as are built on top of the linear dunes Star dunes seem to form in weak wind regimes in which winds blow from different directions in each season resulting in characteristic arms snaking away from a central point Some scientists therefore think the dunes in this image were generated in two earlier climatic phases different from that of today 1 During a phase when winds were stronger and dominantly from one direction the south major linear sand masses accumulated 2 Later when wind strengths declined the star dunes formed Modern-day features known as on the edge of the present erg not shown are younger than either the linear or star dunes and show that present-day sand-moving winds blow from the southwest 2007-02-09 http //earthobservatory nasa gov/IOTD/view php id 7401 NASA -- The featured astronaut photograph eol jsc nasa gov/scripts/sseop/photo pl mission ISS013 roll E frame 75141 ISS013-E-75141 was acquired September 2 2006 with a Kodak 760C digital camera using a 800 mm lens and is provided by the ISS Crew Earth Observations experiment and the Image Science Analysis Laboratory Johnson Space Center The images in this article have been cropped and enhanced to improve contrast The spaceflight nasa gov/home/index html 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 eol jsc nasa gov/ NASA/JSC Gateway to Astronaut Photography of Earth Custom license marker 2012 01 28 Uploaded with UploadWizard Satellite pictures of Algeria Deserts of Algeria Satellite pictures of dunes Star dunes Longitudinal dunes | ||||
