Jebel Marra consists of a pile of mostly basaltic lava which has been covered by pumice and volcanic ash as well as pyroclastic rocks and ignimbrites. The Deriba caldera which forms the top of the entire complex, which around Deriba has the appearance of a large ash cone or shield volcano. Other, less spectacular vents are found elsewhere in the Marra Mountains. Erosion has cut canyons into the volcanic complex. The occurrence of volcanism has been explained with a mantle plume centered between Meidob and Jebel Marra.