Report on Fukutoku-Oka-no-Ba (Japan) — 11 August-17 August 2021
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 11 August-17 August 2021
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2021. Report on Fukutoku-Oka-no-Ba (Japan) (Sennert, S, ed.). Weekly Volcanic Activity Report, 11 August-17 August 2021. Smithsonian Institution and US Geological Survey.
24.285°N, 141.481°E; summit elev. -29 m
All times are local (unless otherwise noted)
JMA reported that a large eruption at Fukutoku-Oka-no-Ba commenced around 0620 on 13 August based on satellite data. Ash plumes rose as high as 16 km (54,000 ft) a.s.l. and drifted W. The eruption was also confirmed during an overflight later that day. Video showed Surtseyan explosions ejecting black material above the ocean’s surface, and ash plumes drifted W. Ash plumes identified in satellite images rose 12.2-16 km (40,000-54,000 ft) a.s.l. during 13-15 August; the height of the plume decreased afterwards though the eruption intermittently continued. The Japan Coast Guard observed a new horseshoe-shaped island that was about 1 km in diameter during an overflight on 15 August. They also observed and photographed a notable pumice raft swirling with the currents as far as 60 km NW. JMA noted that the volcano last erupted in 2010 and frequent episodes of discolored seawater had been observed since then.
Geological Summary. Fukutoku-Oka-no-ba is a submarine volcano located 5 km NE of the island of Minami-Ioto. Water discoloration is frequently observed, and several ephemeral islands have formed in the 20th century. The first of these formed Shin-Ioto ("New Sulfur Island") in 1904, and the most recent island was formed in 1986. The volcano is part of an elongated edifice with two major topographic highs trending NNW-SSE, and is a trachyandesitic volcano geochemically similar to Ioto.