The most prominent feature of the vast Jebel Marra volcanic field, located in the Darfur province of western Sudan, is the youthful Deriba caldera. The 5-km-wide, steep-walled caldera, located at the southern end of the field, 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. The Jebel Marra volcanic field covers a broad area of the Marra Mountains and contains early basaltic lava flows overlain by thick sequences of pyroclastic-flow deposits. The northern part of the field displays trachytic lava plugs and spines forming residual inselbergs and young basaltic scoria cones and lava flows. Ash eruptions at Deriba caldera may have continued into early historical time (Burton and Wickers, 1966), and fumarolic activity has been observed on the flanks of a small pyroclastic cone within the caldera.