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  Image: Geographic Location Direction Photo #: ISS013-E-75141 Date: Sep. 2006
Geographic Region: ALGERIA
Feature: GRAND ERG ORIENTAL

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  Erg Oriental, Algeria:
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 geology. 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 star dunes, 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 wind streaks 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.]
 
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Images: All Available Images Low-Resolution 290k
Mission: ISS013  
Roll - Frame: E - 75141
Geographical Name: ALGERIA  
Features: GRAND ERG ORIENTAL  
Center Lat x Lon: 28.9N x 4.8E
Film Exposure:   N=Normal exposure, U=Under exposed, O=Over exposed, F=out of Focus
Percentage of Cloud Cover-CLDP: 10
 
Camera: E4
 
Camera Tilt: 47   LO=Low Oblique, HO=High Oblique, NV=Near Vertical
Camera Focal Length: 800  
 
Nadir to Photo Center Direction: SW   The direction from the nadir to the center point, N=North, S=South, E=East, W=West
Stereo?:   Y=Yes there is an adjacent picture of the same area, N=No there isn't
Orbit Number: 536  
 
Date: 20060902   YYYYMMDD
Time: 123615   GMT HHMMSS
Nadir Lat: 31.3N  
Latitude of suborbital point of spacecraft
Nadir Lon: 7.0E  
Longitude of suborbital point of spacecraft
Sun Azimuth: 216   Clockwise angle in degrees from north to the sun measured at the nadir point
Space Craft Altitude: 184   nautical miles
Sun Elevation: 62   Angle in degrees between the horizon and the sun, measured at the nadir point
Land Views: DESERT, DUNE  
Water Views:  
Atmosphere Views:  
Man Made Views:  
City Views:  
Photo is not associated with any sequences


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