Kebira Crater (Arabic: فوهة كبيرة) is the proposed name for a circular topographic feature in the Sahara desert. The center of the feature lies in Libya, and the eastern edge extends into Egypt. Its discovery from satellite images was announced in March 2006 by researchers Dr. Farouk El-Baz and Dr. Eman Ghoneim from the Center for Remote Sensing at Boston University, who proposed that it may be an eroded impact crater (astrobleme). They suggested that the crater's original appearance has been obscured by wind and water erosion over time. Detailed field work would be required in order to test the impact hypothesis.
The feature has two rings, the outer of which is 31 kilometres (19 mi) in diameter. If it is an impact crater, it is bigger than the largest confirmed impact crater in the region, the Oasis crater in Libya, which is approximately half the size, with a diameter of approximately 18 kilometres (11 mi). It is estimated that a meteorite large enough to have created a Kebira-sized crater would have been roughly 1 kilometre (0.75 mi) in diameter. As of 2007, the date of the putative impact had not been determined, but it was speculated that it may be related to the yellow-green silica glass fragments, known as "Libyan desert glass", that can be found across part of Egypt's Libyan Desert.
There have been skeptical reactions to the news reports because it is based on speculation about remote sensing data. The Impact Field Studies Group's Impact Database (formerly Suspected Earth Impact Sites, SEIS) list rates this as improbable for an impact origin. The catalog notes that the observed circular area was visible in Google Earth as having a flat top in the center, indicating similar geology to the surrounding area.[1] An impact site should be an isolated area of different geology from its surroundings.[2]
The name of the purported crater is derived from the Arabic word for "large", and also from its location near the Gilf Kebir ("Great Barrier") region in southwest Egypt.
The possible crater was first announced in early March 2006. Several people quickly responded to the announcement by arranging to travel to the site. Two such scientists arrived in Libya in March, and later published their findings: "[C]ontinued north . . towards a large circular feature that was recently announced to be an 'impact crater' . . We drove past the 'central uplift' along its western edge, then drove into the central part. It is evident, that what is considered the 'central uplift' is in fact nothing more than an eroded outlier of the Gilf, the undisturbed horizontal bedding being clearly visible at all times. The circular shape appears to be pure coincidence, the whole feature is the result of drainage patterns and subsequent eolian erosion, there is nothing to suggest its impact origin." And "We were now in the crater area, looking at the western edge of the central uplift area of the 'crater'. What we saw were uniform horizontal layers of sedimentary rocks, undisturbed except by the processes of natural erosion. The jumbled, chaotic rock formation that we would expect to see in the central uplift area of a crater was not evident at all."[3]
A study published in Science reported a field investigation of the Kebira Crater area. After analyzing the presence/absence of several geologic features associated with impact craters, such as target rocks, breccias, pseudo-shatter cones, and circular morphology, the authors concluded: "[T]here are [sic] no clear and unequivocal evidence supporting the impact origin of the circular structures in Glif Kebir region; until substantial evidence is produced, it's necessary to identify the origin of the craters in others [sic] endogenic geological processes." They proposed the most likely alternative source of the crater to be a hydrothermal vent, although they went on to say: "However, even this hypothesis is not fully satisfactory: probably these complex and peculiar features are the result of interaction between different geological process. At present, this hypothesis cannot be completely constrained; further investigations are necessary. Anyway, the lacking of clear evidences of a meteoritic impact and the geological framework of the investigated area, lead us to confirm the hydrothermal-volcanic hypothesis."[4]
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