Tenoumer
Key facts
- Country
- Mauritania
- Diameter
- 1.9 km
- Age
- about 21,000 years
- Location
- 22.92° N, 10.40° W
A strikingly round crater about 1.9 km across with a steep rim rising some 100 m above its flat, sand-covered floor, standing alone in the Sahara Desert.
Tenoumer is one of the most perfect-looking craters on Earth. It rises out of the flat, gravelly plains of the Sahara in north-western Mauritania as a near-circular wall of rock about 1.9 km across, with a sandy floor far below its rim. In satellite images it looks almost like a crater on the Moon.
The impact. Tenoumer formed about 21,000 years ago, during the last Ice Age. At that time the Sahara was going through a dry phase, as it is today, but it has swung between desert and grassland many times. An asteroid struck very hard, ancient granite and gneiss, blasting out a bowl-shaped crater. The rim now rises about 100 m above the floor, which has been partly filled by wind-blown sand and lake sediments from wetter periods.
Volcano or impact? Tenoumer's origin was debated for decades. Because some of its rocks looked like lava, some geologists argued that it was a volcanic explosion crater. Others pointed to its sharp, circular shape and its setting in solid ancient crust as signs of an impact. The question was settled by the discovery of impact melt rock in and around the crater, rock that had been melted by the energy of the impact and contains fragments of the surrounding granite. Studies found shocked minerals and glass consistent with an impact.
Dating the crater. The crater's age was measured from the melt rock, giving an age of roughly 21,000 years. That makes Tenoumer one of the youngest craters of its size on Earth. Its youth explains its excellent state of preservation: in a dry climate, with little rain or vegetation, erosion is very slow.
Life in the desert. The crater floor sometimes holds moisture after rare rains, and patches of vegetation can grow there. The surrounding area is very sparsely populated and visited mainly by nomadic herders and occasional scientists.
Why it matters. Tenoumer is a textbook example of a simple crater, a bowl-shaped crater without a central peak. Craters smaller than about 2 to 4 km on Earth usually take this form, while larger ones collapse to form central peaks or rings. Tenoumer is well below the size at which craters in hard rock develop central peaks, making it a clean example for comparison with craters on the Moon and Mars.
Visiting. Tenoumer is remote, lying in a sparsely populated desert region. Travel in this part of Mauritania requires careful planning, local guides and up-to-date advice on safety and access.
Did you know?
Tenoumer was long thought by some to be volcanic until impact melt rock was found.
It formed around the time of the last Ice Age, about 21,000 years ago.
In satellite images its near-perfect circle looks like a crater on the Moon.