Emi Koussi

The volcano is 60–70 kilometres (37–43 mi) wide and has a volume of 2,500 cubic kilometres (600 cu mi). Two nested calderas cap the volcano, the outer one being about 15 by 11 kilometres (9.3 mi × 6.8 mi) in size. Within it on the southeast side is a smaller caldera known as Era Kohor, about 2 kilometres (1.2 mi) wide and 350 metres (1,150 ft) deep. Numerous lava domes, cinder cones, maars, and lava flows are found within the calderas and along the outer flanks of the shield. Era Kohor contains trona deposits, and Emi Koussi has been studied as an analogue of the Martian volcano Elysium Mons. Emi Koussi was active more than one million years ago, but some eruptions may be more recent, and there is ongoing fumarolic and hot spring activity. Emi Koussi lies in Chad, Africa, and is part of the Tibesti Mountains as well as its highest peak and thus of the Sahara; many peaks of the Tibesti exceed 2,000 metres (6,600 ft) in height. These mountains are formed by a group of volcanoes that grew on top of a large dome of Earth's surface.