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Report on Fukutoku-Oka-no-Ba (Japan) — July 1987


Scientific Event Alert Network Bulletin, vol. 12, no. 7 (July 1987)
Managing Editor: Lindsay McClelland.

Fukutoku-Oka-no-Ba (Japan) Submarine eruptions; floating pumice

Please cite this report as:

Global Volcanism Program, 1987. Report on Fukutoku-Oka-no-Ba (Japan) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 12:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198707-284130



24.285°N, 141.481°E; summit elev. -29 m

All times are local (unless otherwise noted)

On 14 July at about 1240, discolored and spouting seawater was reported by observers on a fishing boat. Sprays reached 10 m above the water surface for about a minute at intervals of 10-15 minutes. The next day, 100-150-m-diameter, circular, white-crested waves with spouts in their centers formed at intervals of 6 minutes throughout a 50-minute JMSA overflight. Some floating pumice was found within a zone of yellowish-green seawater that was 500 m wide and stretched 18 km E. No white-crested waves formed after 16 July. During a 17 July overflight, a 30-100 m-wide area of green seawater extended 13 km E. Pumice floated at the E end of this area. On 21 July discolored seawater spread out from two points and minor amounts of pumice were floating in the area. On 30 July deep-green discolored water extended as far as 9 km E over an area 0.5-2 km wide and contained floating brown pumice.

Geological Summary. Fukutoku-Oka-no-ba is a submarine volcano located 5 km NE of the pyramidal island of Minami-Ioto. Water discoloration is frequently observed from the volcano, 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.

Information Contacts: JMA.