Volcano Islands in Izu-Mariana arc

(24o16'N, 141o29'E)

(June 16, 1997)
Discoloring of sea surface around Fukutoku-Okanoba was frequently observed during February-May. The maximum discolored area reached 5,000 m by 560 m on February 17. Generally, it was yellowish green to pale green in color, but white nebulous around the points from which water gashed out. On May 1, a white-discolored belt extended up to 1,800 m long from the point, with floating materials (bubbles or pumices?).

Information contact: Maritime Safety Agency in Japan

(February 10, 1997)
Discoloring of Sea surface in the submarine volcano, Fukutoku-Okanoba was observed by aircrafts of the Marine Self-Defense Forces and Maritime Safety Agency on 15 October, 28 November, 9, 12 and 16 December, and 27 January 1997. The yellowish green- to green-colored area extended up to 2000 m long and 100 m wide in January 1997.

Information contact: Maritime Safety Agency in Japan

Discolored sea surface was observed again on September 6 and 18 by the air craft of Hydrographic Department. The areas of 150 m long x 50 m wide and 500 m long x 300 m wide, colored in yellowish green, were located about 1.5 miles NNE of Minami-Iwojima Volcano.

According to Hydrographic Department, colored sea surface was not recognized from the air on 23 May. The activity of coloring sea surface that had been observed since March, was thought to have been in the highest level in the end-April.

Yellowish brown-colored sea-area was observed at Fukutoku-okanoba (or Fukutoku-Oka-no-Ba) from an airplane by Maritime Safety Agency (MSA), Ministry of Transport, Japan, on 4 April 1996. According to Hydrographic Department of MSA, the colored area expanded like a belt up to about 3 km long. Strong emission of colored water was recognized from two points. Although white-colored suspension was observed on the surface, floating pumices were not recognized. Smaller-scale of the same phenomena had been observed since 24 November 1995.

Yellowish green- to yellowish brown-colored area was still observed from the air on 12 April. The colored zone, about 4 km long and 200 m wide, included 3 to 4 spots from which colored-water was gushing out intermittently. No pumices were recognized on the sea surface.
Information Contact: Tohru Tsukamoto, Hydrographic Department, MSA

Fukutoku-okanoba is an andesite submarine volcano (roughly 15 m below the sea level), located 5 km NE of Minami-Iwojima Volcano, and 50 km SE of Iwojima Volcano. The volcano appeared above the sea surface in 1904, 1914, and 1986; all the times, it disappeared due to wave erosion less than two years after the appearance. In 1914, the volcano had towered about 300 m high with the circumference of about 12 km.

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