Physical volcanology of the Gubisa Formation, Kone Volcanic Complex, Ethiopia

Despite their significance for understanding the potential environmental factors involved in hominin evolution in Ethiopia, very few modern volcanologic studies have been carried out on the Quaternary calderas and associated silicic tephra deposits of the Ethiopian Rift. We present here the second of a set of papers reporting the findings of fieldwork and laboratory analyses of one of the largest of these structures, Kone Caldera, located within the Kone Volcanic Complex in the northern Main Ethiopian Rift. The most recent major episode of explosive eruptive activity at Kone Caldera was apparently associated with formation of part of the overall 8-km-diameter collapse area, and deposited a widely-dispersed alkali rhyolite tephra that reaches a thickness of up to 60 m in vent-proximal deposits. We report here the physical characteristics of this unit in order to constrain eruptive conditions. The pumice fall deposit suggests that an abrupt decrease in magma discharge rate occurred part way through the eruption.