A lake partially fills a younger cone within the Deriba caldera of Jebel Marra volcano in this view from the N. The 5-km-wide, steep-walled caldera, whose wall appears in the background, was formed about 3,500 years ago at the time of the eruption of voluminous airfall pumice and pyroclastic flows that traveled more than 30 km from the volcano. Post-caldera ash eruptions may have continued into historical time. Photo by J. Williams, 1986 (http://en.wikipedia.org/wiki/Image:Sudan_Jebel_Marra_Deriba_Lakes.jpg)