The plateau was formed by flows of basaltic lavas that filled two broad valleys eroded into the Precambrian basement, followed by further flows that built up the plateau. There are many trachyte and phonolite plugs across the plateau, and lines of cinder cones from the most recent eruptions.[1] The plateau contains Tchabal Nganha, a large stratovolcano of basanitic to trachytic composition.[2] Nganha is about 1,000 m high.