24. Gweni Fada, Chad
The Gweni Fada structure was first noted on Landsat images and aerial photography. Later (in the early 1990s), a team of French geologists visited the site and reported evidence of shock metamorphism within rock samples they had collected inside the structure. Erosion and infilling have modified the original crater topography, yet structural and lithological variations delineate the feature clearly. The most prominent expression of the crater is a bright crescent-shaped depression located near the center of the image. This depression encloses the southern two-thirds of an 8–10-kilometer-wide elevated region containing strongly disturbed blocks of sandstone; this probably corresponds to the eroded crater's central peak. The crescent itself is ~12 kilometers in diameter and probably represents the vestiges of the original crater floor. The material composing the surface of the crescent appears similar to the sediments occupying nearby streambeds. Surrounding the central zone to the north, and the crescent-shaped depression elsewhere, is an elevated rim consisting of outwardly dipping sandstone.
Space shuttle image STS51G-37-034.