Gweni-Fada
Key facts
- Country
- Chad
- Diameter
- 14 km
- Age
- less than 345 million years
- Location
- 17.42° N, 21.75° E
An eroded ring of sandstone ridges about 14 km across in the Ennedi region of the Sahara, clearest in satellite images.
Gweni-Fada is a crater that was found from space. It lies in the Ennedi region of north-eastern Chad, a remote area of sandstone plateaus, canyons and rock arches in the eastern Sahara. On the ground it is a broken landscape of eroded ridges; from orbit it appears as a clear ring about 14 km across.
Discovery. Gweni-Fada was first noticed as a circular feature in images taken from space. Geologists suspected it might be an impact crater because of its round shape and the way its rock layers were disturbed. Field samples collected later were examined under the microscope, and shocked quartz was found. Shocked quartz contains sets of microscopic parallel planes, called planar deformation features, which form only under the extreme pressures of a shock wave. That evidence confirmed an impact, and Gweni-Fada was added to the list of proven impact structures in the mid-2000s.
Age and structure. The crater was blasted into sandstones of Devonian age, so it must be younger than those rocks, less than about 345 million years old. Beyond that its age is unknown. Like its neighbour Aorounga, about 300 km to the north-west, it has been deeply eroded by wind and occasional water. What remains is a ring of uplifted and folded rock around a central area, the roots of a complex crater that once had a central uplift.
Saharan craters. The Sahara is one of the best places on Earth to look for impact craters. Its dry climate means there is little vegetation to hide the rocks, and erosion is slow. Satellite and astronaut images have revealed many circular structures across the desert, and fieldwork has confirmed a number of them as impacts, including Aorounga and Gweni-Fada in Chad, Tenoumer in Mauritania and the tiny, very young Kamil crater in Egypt. Many other suspected structures still await proper study, because the region is so remote.
Why it matters. Gweni-Fada shows how space-based imaging has become a powerful tool for finding impact craters. It also illustrates the rule that a circular shape alone is not enough: every suspected crater must be confirmed by evidence of shock in its rocks. Many circular features in the Sahara and elsewhere have turned out to be volcanic, tectonic or caused by erosion.
The Ennedi. The surrounding Ennedi Massif is a UNESCO World Heritage Site, known for its spectacular sandstone landscape, rock art and wildlife, including desert-adapted crocodiles in some permanent pools. Travel in the region is difficult and requires careful planning, local guides and up-to-date safety advice.
Did you know?
Gweni-Fada was first spotted in images taken from space.
Shocked quartz from its rocks proved that it was made by an impact.
It lies in the Ennedi region, famous for its sandstone arches and ancient rock art.