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.
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.
|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||--|
Geologic Background. 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: Hydrographic Department, JMSA.