Dynamics of the 7.3 ka caldera-forming eruption and its magma chamber condition in the Kikai caldera, Japan

Abstract

Stratigraphy, component, and lithology of the pyroclastic deposits in the 7.3 ka eruption of the Kikai caldera were analyzed in order to reconstruct the eruption. The duration of the plinian stage is estimated to be more than 28 h, based on the thickness and clast-size data of the fallout deposits. The sedimentary characteristics resulted from the plinian column collapse indicate that high temperature density currents were generated. In the final phase, multiple pyroclastic density currents were followed by the main sustained current. In total the estimated magma volume in the system was 70-80 km³ in DRE, with compositional range of andesite to rhyolite spanning with the climactic phase. The caldera collapse duration was estimated to be less than 6 hours, based on tsunami numerical simulation combined with simple caldera collapse model, magma chamber condition, and coastal geological data.