Seawater-magma interactions sustained the high column during the 2021 phreatomagmatic eruption of Fukutoku-Oka-no-Ba

Abstract

Phreatomagmatic eruptions are among the most hazardous types of volcanic eruptions on Earth. Here, we show how rapidly ascended magma interacted with seawater in a shallow sea environment based on a high-resolution timeseries record of a sizeable phreatomagmatic eruption that occurred at the Fukutoku-Oka-no-Ba volcano, Ogasawara, on 13 August 2021. The eruption started on the seafloor at a depth of <70 m and breached the sea surface to produce a 16 km-high, water-rich sustained eruption column. The magma volume, ~0.1 km3, including the tuff cone and the pumice raft, is consistent with SO2 emissions estimated from satellite observations and geochemistry. Most eruption and deposit observations can be explained by the effective near-vent accumulation of pyroclasts emitted during jet-seawater interactions fed by magma discharging at a rate of 3–6 × 105 kg/s. Our results contribute to understanding the dynamics and hazards of shallow submarine volcanism.