First timeseries record of a large-scale silicic shallow-sea phreatomagmatic eruption

Abstract Phreatomagmatic eruptions are one of the most common styles of volcanic eruptions on Earth1–2. Recent studies have highlighted the importance of the eruption depth and magma discharge rate on the eruptive behaviour of underwater volcanoes2–7. Even though voluminous silicic eruptions in shallow-water environments are likely to be intense and hazardous, such eruptions mostly appear in geological records7–12 and the nature of this type of eruption is therefore poorly understood. Here, we show the first timeseries record of a large-scale silicic phreatomagmatic eruption that occurred at the Fukutoku-Oka-no-Ba volcano, Ogasawara, Japan, on 13 August 2021. The eruption started on the seafloor at a depth of < 70 m and breached the sea surface, resulting in a 16-km-high, steam-rich sustained eruption column. The total magma volume was ~ 0.1 km3, including the subaerial tuff cone and the 300-km2 pumice raft, most of which can be explained by the effective accumulation of pyroclasts near the vent resulting from interactions between the eruption plume and the ambient water. This eruption provides a rare opportunity to investigate the process of a large-scale phreatomagmatic eruption in a shallow sea and contributes to our understanding of the nature, dynamics, and hazards of submarine volcanism.