The Aïr Massif in Niger. Public Domain by NASA Earth Observatory images by Robert Simmon and Jesse Allen, using Landsat data from the USGS Earth Explorer and the LANCE/EOSDIS MODIS Rapid Response Team at NASA GSFC. Caption by Holli Riebeek. Aïr and Ténéré Natural Reserves.
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Original caption reads:
The dark round domes of the Aïr Mountains rise out of the Sahara Desert, a chain of islands in a sea of sand. Geologically, the mountain massif in Niger is not that different from an island. It formed when magma flowed in to pre-existing cracks and caverns in the bedrock, a geologic formation called a dike. The bubble-shaped mounds are ring dikes, which formed when the ceiling of a magma chamber collapsed, leaving a circular crack that was later filled with magma. Through time and the constant movement of Earth’s crust, these magma intrusions have been lifted and moved together, an isolated piece of geology different from its surroundings. The mountains are now 2,000 meters (7,000 feet) tall.
These images show both the unique geology of the ring dikes and the relative isolation of the formation. The Operational Land Imager on the Landsat 8 satellite acquired the top image on May 26, 2013. Cracks cross the rock formation, a product of weathering and faulting. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired the lower image on May 25, 2013. This view provides wider context, showing how different the mountains are from their surroundings. (The formation looks even more isolated in this astronaut photo taken on March 23, 2010, just before a dust storm blanketed the mountains.)
This circular formation looks similar to the Brandberg Mountain, at least as seen from satellite. Both are granitic:
However, if we assume that electricity is able to create granite almost instantly, should we reconsider these formations? See “Instant high grade metamorphic granite”, from Michael Steinbacher‘s youtube channel.
Also, Thunderbolts website has an article on the Brandberg Massif which argues for an electric origin of such formations.