Aorounga
Key facts
- Country
- Chad
- Diameter
- 12.6 km
- Age
- less than 345 million years
- Location
- 19.10° N, 19.25° E
An eroded ring of ridges about 13 km across, carved by desert winds into long parallel ridges and troughs, best appreciated from the air or in satellite images.
Aorounga lies deep in the Sahara in northern Chad, in one of the most remote and wind-swept landscapes on Earth. Seen from space, it is a striking sight: a ring of ridges about 13 km across, sitting among long parallel bands of rock and sand sculpted by the wind.
The impact. The crater formed when an asteroid struck sandstone layers laid down in the Devonian or early Carboniferous. Because those rocks are about 345 million years old or more, the crater must be younger than that. Its exact age is unknown. The structure is heavily eroded, and what remains is a central uplift surrounded by a ring-shaped trough and an outer rim.
Carved by the wind. The most remarkable thing about Aorounga is the way it has been shaped by erosion. Northern Chad is battered by strong, steady winds blowing from the north-east, and over a very long time these winds, carrying sand, have scoured the rocks into long parallel ridges called yardangs, separated by troughs. The ring of the crater cuts across this pattern of stripes, creating a dramatic image.
A chain of craters? In 1994 radar on the Space Shuttle, which can see through thin layers of dry sand, imaged the area. The radar images suggested there might be one or two more ring structures next to Aorounga, similar in size, forming a line. If confirmed, this would mean that a broken-up asteroid made a chain of craters, a type of impact sometimes seen on the Moon. However, the additional structures have not been confirmed as impact craters, and only the main crater is listed as proven.
Proof of impact. Aorounga's impact origin is supported by shocked quartz found in its rocks, together with its circular structure and central uplift.
Seeing it today. Aorounga lies in the Borkou region of northern Chad, close to the Tibesti and Ennedi areas, in a region that is extremely difficult to reach. Few scientists have visited it, and most of what we know comes from satellite and astronaut images combined with a small number of field studies. For most of us, the best way to see Aorounga is in the many striking images taken from orbit.
Why it matters. Aorounga is a good example of how erosion modifies craters, and of how space-based imaging can find and study features that would be very hard to examine on the ground. Several other impact structures in the Sahara, including Gweni-Fada, were first recognised in images taken from space.
Did you know?
Radar from the Space Shuttle hinted that Aorounga might be one of a chain of craters.
Desert winds have carved the surrounding rock into long parallel ridges called yardangs.
Most people know Aorounga from images taken from space.