The broad Emi Koussi volcano, as seen in this astronaut photograph is a shield volcano located in northern Chad, at the southeastern end of the Tibesti Range.
The dark volcanic rocks of the volcano provide a sharp contrast to the underlying tan and light brown sandstone exposed to the west, south and east (image lower left, lower right and upper right).
Emi Koussi was formed from relatively low viscosity lavas flowing more like motor oil than toothpaste and explosively-erupted ignimbrites (rapid flows of hot volcanic material dominated by pumice, a light, porous volcanic rock) that produce a characteristic low and broad structure covering a wide area (approximately 37 by 50 miles, or 60 by 80 kilometers).
Two older and overlapping calderas form a depression approximately 7.5 by 9.3 miles (12 kilometers by 15 kilometers) in area bounded by a distinct rim (image center). The youngest and smallest caldera, Era Kohor, formed as a result of eruptive activity within the past 2 million years.
Young volcanic features, including lava flows and scoria cones (also called cinder cones) are also thought to be less than 2 million years old. There are no historical records of eruptions at Emi Koussi, but there is an active thermal area on the southern flank of the volcano, according to a NASA statement.