Featured astronaut photograph ISS015-E-15323 was acquired June 27, 2007, by the Expedition 15 crew with a Kodak 760C digital camera using a 70 mm lens. The image is provided by the ISS Crew Earth Observations experiment and the Image Science & Analysis Laboratory, Johnson Space Center. The image in this article has been cropped and enhanced to improve contrast. 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.
The Béchar Basin of northwest Algeria formed as layers of sedimentary rocks from the Paleozoic Era (250-540 million years ago) folded and cracked during collisions of Africa and Europe during the Tertiary Period (2-65 million years ago). Hydrocarbon (coal, oil) reservoirs are tucked among the fragments of sedimentary rocks and fossilized coral reefs that make up the basin’s rock layers, which are up to 8,000 meters thick. In this photograph of part of the basin captured by astronauts on the International Space Station on June 27, 2007, dark brown to tan folded ridges of these Paleozoic sedimentary layers extend across the image from top to bottom.
Sand dunes are visible to the north, south, and west of the city of Béchar (gray-blue region to the left of the ridges) at image center. Wadis (river channels) are dry most of the year in the arid climate of the region. Unconsolidated (loose) sands left in the channels by intermittent streams are transported by surface winds after the water is gone. This leads to the formation of individual dunes and larger dune fields (both bright tan in color) along the wadi courses, which also concentrate sands from other sources; dune fields are visible to the south of Béchar and at image lower right. The oblique view (looking at an angle, not straight down, from the International Space Station) of this astronaut photograph accentuates cliff and dune shadows, providing a sense of the topography of the region.
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This image originally appeared on the Earth Observatory. Click here to view the full, original record.