08 Jan '12, 11pm

Emi Koussi and Aorounga, Chad: Two neighboring craters in Africa had very different origins.

This striking photograph from the International Space Station features two examples of circular landscape features—labeled as craters—that were produced by very different geological processes. At image right, the broad grey-green shield volcano of Emi Koussi is marked by three overlapping calderas that were formed by eruptions. The calderas form a large, oblong depression at the 3,415–meter (11,200 foot) high summit of the volcano. A smaller crater sits within the larger caldera depression. While volcanic activity has never been observed—nor mentioned in historical records—an active thermal area can be found on the southern flank. The circular Aorounga Impact Crater lies approximately 110 kilometers (68 miles) to the southeast of Emi Koussi and has its origins in forces from above rather than below. (Note that the image is rotated so that north is at the bottom.) The Aorou...

Full article: http://earthobservatory.nasa.gov/IOTD/view.php?id=76894&s...

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Emi Koussi and Aorounga, Chad: Two neighboring ...

earthobservatory.nasa.gov 08 Jan '12, 11pm

This striking photograph from the International Space Station features two examples of circular landscape features—labeled...

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earthobservatory.nasa.gov 08 Jan '12, 11pm

This striking photograph from the International Space Station features two examples of circular landscape features—labeled...

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earthobservatory.nasa.gov 09 Jan '12, 12am

This striking photograph from the International Space Station features two examples of circular landscape features—labeled...

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earthobservatory.nasa.gov 13 Jan '12, 6pm

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