Dubbi volcano, located in the northeast part of the Afar triangle, erupted explosively in May 1861, showering maritime traffic in the Red Sea with pumice and plunging coastal settlements into darkness. Earthquakes associated with the opening phase of the eruption were felt in Yemen, and explosions were heard as far as Massawa, 330 km distant. More than 100 local inhabitants were reported killed, possibly as a result of pyroclastic flow emplacement. By October 1861, activity switched to basaltic fire-fountaining focused along a 4-km-long summit fissure that fed several lava flows that traveled as far as 22 km. We present a reconstruction of this unusual explosive and effusive eruption sequence based on interpretation of contemporary accounts, analysis of satellite imagery, field work, and laboratory geochemistry. The volume of lava flows alone, 3.5 km3, makes this the largest reported historical eruption in Africa. An anomalously cold Northern Hemisphere summer in 1862, recorded in tree-ring records, could be the result of Dubbi's sulfate aerosol veil.