A new phreatomagmatic eruption took place at the volcano on 1 September.
At about 07:14 PM local time, a mixture of dark black volcanic ash, lapilli, glowing bombs and seawater was being thrown to a height of several dozen meters above sea level. A certain amount of lighter pumice was also present in the ash, probably representing a batch of fresh magma that had driven the explosion. A pumice raft has been observed floating towards the other side of the island.
The eruption formed a new crater called Chidorihama, from which a white-to-grey ash plume continues to rise.
Phreatomagmatic activity means that erupting magma reacts with external water, e.g. ground water, lake water, sea water etc.
Prior to the eruption, several crustal movements had been detected as magma pressurized and fractured rocks at depth. In addition, several fumarolic vents were accompanied by strong steam-laden plumes. Sulfur dioxide is contained in solution in magma at greater depths, but when magma is closer to the surface and under less pressure, most if it is released as its solubility decreases with decreasing pressure, thus leaves magma and its way to the surface through cracks. Since gas is much more mobile than the molten rock itself, it is typically arriving at the surface before an eruption starts.
Source: Japan Meteorological Agency volcano activity update 8 September 2025
