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Posts tagged Richat Structure

Richat Structure in the Sahara Desert of Mauritania

21.1N 11.4W

February 3rd, 2010 Category: Mountains, Snapshots

Mauritania - January 8th, 2010

Mauritania - January 8th, 2010

This pattern of concentric circles in the Saharan Desert near Ouadane, in Mauritania, is known as the Richat Structure. Due to its bullseye-like shape, it was originally believed to be a crater from a meteorite impact. However, scientists now believe that it is a circular anticline whose crest has been eroded away.

The structure is at least 40 km in diameter. Erosion has created circular cuestas represented by three nested rings dipping outward from the structure. The center of the structure consists of a limestone-dolomite shelf that encloses a kilometer-scale siliceous breccia and is intruded by basaltic ring dikes, kimberlitic intrusions, and alkaline volcanic rocks.

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Spiral of Dust off Coast of Morocco – July 27th, 2009

22.5N 12.5W

July 27th, 2009 Category: Dust Storms, Image of the day

Dust of coast of Morocco - July 26th, 2009

Dust of coast of Morocco - July 26th, 2009

Dust blowing off the coast of Morocco, Western Sahara and Mauritania takes on a loose spiral shape that appears to swirl counter-clockwise. The vortex of dust stretches from the Canary Islands (above) to Ras Nouadhibou (Cap Blanc) at the border with Mauritania (below).

Inland, the bulls-eye shaped Richat Structure and the Kediet ej Jill mountain are visible in the lower right quadrant. Appearing here as a dark brown circular area northwest of the Richat Structure, Kediet ej Jill is the highest peak in Mauritania at 915 meters tall.

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The Richat Structure, Mauritania – April 24th, 2009

April 24th, 2009 Category: Image of the day

Morocco and Mauritania - April 9th, 2009

Morocco and Mauritania - April 9th, 2009

Richat Structure - source: NASA

Richat Structure

The Ras Nouadhibou Peninsula (upper left) marks the border Morocco’s Western Sahara (above) and Mauritania (below). The Gulf of Arguin, lies just south of the peninsula.

Another border, between Mauritania and Senegal, is marked by the Senegal River.

Moving inland from the Atlantic Ocean into Mauritania, an odd, circular feature can be observed (open full image for best view). This is the Richat Structure, a prominent ringed indentation in the Sahara desert near Ouadane.

It has attracted attention since the earliest space missions because it forms a conspicuous bull’s-eye in the otherwise rather featureless expanse of the desert. The structure has a diameter of almost 50 kilometres (30 miles).

Initially interpreted as a meteorite impact structure because of its high degree of circularity, it is now thought to be a symmetrical uplift (circular anticline or dome) that has been laid bare by erosion. Paleozoic quartzites form the resistant beds outlining the structure.

The close-up image is a false-colored topographic reconstruction from satellite photos. The false coloring shows the geological composition and vegetation of the area using the following color scheme: bedrock is brown, sand is yellow or white, vegetation is green, and salty sediments are blue.

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