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Report on Fukutoku-Oka-no-Ba (Japan) — December 1990


Bulletin of the Global Volcanism Network, vol. 15, no. 12 (December 1990)
Managing Editor: Lindsay McClelland.

Fukutoku-Oka-no-Ba (Japan) Frequent observations of discolored water

Please cite this report as:

Global Volcanism Program, 1990. Report on Fukutoku-Oka-no-Ba (Japan) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 15:12. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199012-284130



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

All times are local (unless otherwise noted)

Aerial observations of the ocean surface above the submarine volcano revealed discolored water in January-May, September, and November (table 2). The longest discoloration, 8 km, was observed during an overflight on 17 January. Thermal activity has continued since the January 1986 eruption . . . . Discolored water has been frequently observed since that time (14:07). No discolorations were observed at other submarine volcanoes (Kaitoku, Minami-Hiyoshi, Nikko, and Fukujin seamounts) during 1990.

Table 2. Discolored water at Fukutoku-Okanoba, observed from monthly overflights in 1990. Courtesy of JMSA.

Date Water Color Length of Discoloration
17 Jan 1990 yellowish brown 8 km
20 Feb 1990 green 7 km
27 Mar 1990 green and brown 1.8 km
17 Apr 1990 blue 0.3 km
16 May 1990 blue 0.05 km
Jun 1990 no discoloration --
Jul 1990 no discoloration --
Aug 1990 no discoloration --
13 Sep 1990 pale green 3.6 km
15 Oct 1990 no discoloration --
20 Nov 1990 yellowish green 0.7 km
Dec 1990 no discoloration --

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.

Information Contacts: Hydrographic Department, JMSA.