This paper investigates the 2021 phreatomagmatic eruption at Fukutoku-Oka-no-Ba volcano. The eruption, starting at a depth of <70 m, produced a 16 km-high eruption column sustained by rapid magma ascent and seawater interaction. The study uses high-resolution timeseries data from satellites and infrasound to analyze the eruption's four phases. Magma volume (~0.1 km³) is consistent with SO₂ emissions. The eruption dynamics are explained by near-vent pyroclast accumulation from jet-seawater interactions, with a magma discharge rate of 3–6 × 10⁵ kg/s. The findings contribute to understanding shallow submarine volcanism dynamics and hazards.
