Aluto is a silicic volcano in central Ethiopia, flanked by two large population centers and home to an expanding geothermal power plant. Here we present data from two lake sediment cores sampled 12 and 25 km from the volcano, which record at least 24 distinct eruptions in the Holocene. Tephra layers from the two cores are correlated using a variety of techniques, including major and trace element geochemistry as well as textural and morphological features from scanning electron

more »

... atter electron imaging. The purpose is to provide a Holocene reference section for further tephrostratigraphic studies of the volcano as well as to provide information on eruption frequency. The lake cores suggest that Aluto has had a variable eruption rate, with three eruption clusters in the Holocene at ~3, 6.5, and 11 ka, with small Vulcanian-to sub-Plinian eruptions separated by larger, Plinian eruptions. We infer that the smaller tephras are likely the product of pumice cone-and dome-forming eruptions. In addition, modern wind data suggest that the likely direction of an ash cloud from Aluto is to the west and south west, which is toward population centers and is in agreement with thickness data from the cores. We conclude that current records underestimate the volcano's eruptive history and that hazard assessments should be updated accordingly. Plain Language Summary In this study we explore the history of a populated volcano in central Ethiopia called Aluto. The volcano is close to several large towns and home to an expanding geothermal power plant. Aluto has not erupted in the last few hundred years, and so there are no eye witness accounts of volcanic activity. In lieu of this, we use volcanic material deposited in the surrounding environment during an eruption as a record of the volcano's activity. In this study, we examine the volcanic material deposited in two lakes using lake cores drilled ~12 and 27 km from the volcano that record the eruptive history from 2,000 to 12,000 years ago. These cores record 24 volcanic eruptions; which indicates an eruption every ~250 years. We use features of the volcanic ash particles to match up eruptions in the cores and to establish when the eruptions occurred. We find that the volcano has had three periods of increased activity, each lasting around 1,000 years. As such, we can infer that the volcano has erupted frequently over the last 10,000 years and hazard assessments of the volcano should be updated accordingly.