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

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, linked the initial 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.

Fukashi Maeno, Takayuki Kaneko, Mie Ichihara, Yujiro J. Suzuki, Atsushi Yasuda, Kiwamu Nishida, Takao Ohminato