West Africa - Richat Structure

NASA/JPL/NIMA. "AfricaSRTM-RichatStructure-picasa.jpg" Online Image. Shuttle Radar Topography Mission. 20 Jan. 2006 87kb. 778x428px. <http://photojournal.jpl.nasa.gov/catalog/PIA04963>

West Africa - Richat Structure

This image shows a perspective view created by draping a Landsat image over the elevation framework from an SRTM data set for the Richat Structure. It was created from an original map produced from data obtained by NASA's Shuttle Radar Topography Mission (SRTM). Using Google's free Picasa2 program, the color, contrast, and lighting were enhanced. It was then sharpened to obtain the image above. The original image can be viewed at the NASA link above.

This prominent circular feature, known as the Richat Structure, in the Sahara desert of Mauritania is often noted by astronauts because it forms a conspicuous 50-kilometer-wide (30-mile-wide) bull's-eye on the otherwise rather featureless expanse of the desert. Initially mistaken for a possible impact crater, it is now known to be an eroded circular anticline (structural dome) of layered sedimentary rocks. Extensive sand dunes occur in this region and the interaction of bedrock topography, wind, and moving sand is evident in this scene. Note especially how the dune field ends abruptly short of the cliffs at the far right as wind from the northeast (lower right) apparently funnels around the cliff point, sweeping clean areas near the base of the cliff. Note also the small isolated peak within the dune field. That peak captures some sand on its windward side, but mostly deflects the wind and sand around its sides, creating a sand-barren streak that continues far downwind.

This view was generated from a Landsat satellite image draped over an elevation model produced by the Shuttle Radar Topography Mission (SRTM). The view uses a 6-times vertical exaggeration to greatly enhance topographic expression. For vertical scale, note that the height of the mesa ridge in the back center of the view is about 285 meters (about 935 feet) tall. Colors of the scene were enhanced by use of a combination of visible and infrared bands, which helps to differentiate bedrock (browns), sand (yellow, some white), minor vegetation in drainage channels (green), and salty sediments (bluish whites). Some shading of the elevation model was included to further highlight the topographic features.

View Size: 68 kilometers (42 miles) wide by 112 kilometers (69 miles) distance
Location: 21.2 degrees North latitude, 11.7 degrees West longitude
Orientation: View toward west-northwest
Image Data: Landsat Bands 1, 4, 7 in B.G.R.
Date Acquired: February 2000 (SRTM), January 13, 1987 (Landsat)

NASA/JPL/NIMA. Shuttle Radar Topography Mission. 20 Jan. 2006 <http://photojournal.jpl.nasa.gov/catalog/PIA04963>