Aorounga crater
Posted: Sat Aug 15, 2009 2:46 am
--------------------------------------------------http://en.wikipedia.org/wiki/Aorounga_crater wrote:
<<Aorounga is an eroded meteorite impact crater in Chad, Africa. The exposed remnant of the crater is 12.6 km in diameter and its age is estimated to be less than 345 million years (Carboniferous or younger).
The crater is accompanied by two nearby circular features revealed by Space Shuttle SIR-C radar. These may be related impact craters, and if correct, Aorounga may be part of a crater chain. On the assumption that this hypothesis is correct, the exposed Aorounga crater is sometimes referred to as Aorounga South.>>
--------------------------------------------------http://earthobservatory.nasa.gov/IOTD/view.php?id=39727 wrote:
<<Aorounga Impact Crater is located in the Sahara Desert, in north-central Chad, and is one of the best-preserved impact structures in the world. The crater is thought to be middle or upper Devonian to lower Mississippian (approximately 345–370 million years old) based on the age of the sedimentary rocks deformed by the impact.
Spaceborne Imaging Radar (SIR) data collected in 1994 suggests that Aorounga is one of a set of three craters formed by the same impact event. The other two suggested impact structures are buried by sand deposits.
The concentric ring structure of the Aorounga crater—renamed Aorounga South in the multiple-crater interpretation of SIR data—is clearly visible in this detailed astronaut photograph. The central highland, or peak, of the crater is surrounded by a small sand-filled trough; this in turn is surrounded by a larger circular trough. Linear rock ridges alternating with light orange sand deposits cross the image from upper left to lower right; these are called yardangs by geomorphologists. Yardangs form by wind erosion of exposed rock layers in a unidirectional wind field. The wind blows from the northeast at Aorounga, and sand dunes formed between the yardangs are actively migrating to the southwest.>
http://earthobservatory.nasa.gov/IOTD/view.php?id=39769 wrote:
<<Meteorites continue to strike both the Earth and Moon. Micrometeorites bombard the Earth continuously. Larger asteroids hit Earth less frequently. Asteroids measuring roughly 50 meters across strike the Earth every 1,000–2,000 years, while more than 100,000 years typically elapse between strikes from asteroids larger than 1,000 meters across.
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