||Emi Koussi Volcano, Chad |
Note: This caption refers to the image versions labeled "NASA's Earth Observatory web site".
The broad Emi Koussi volcano 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 that produce a characteristic low and broad structure covering a wide area (approximately 60 by 80 kilometers).
This astronaut photograph highlights the entire volcanic structure. At 3,415 meters above sea level, Emi Koussi is the highest summit of Africa's Sahara region. The summit includes three calderas formed by powerful eruptions. Two older and overlapping calderas form a depression approximately 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 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.