Active volcanoes / Aktive vulkaner:
Fukutoku-Okanoba, Japan

Fukutoku-Okanoba and vicinity shown in a 3-dimensional diagram, with color representing various elevation ranges;
vertical exaggeration is considerable but was not stated.

Copyrighted image courtesy of the Japan Coast Guard.

Fukutoku-Okanoba is a submarine volcano located 5 km NE of the pyramidal island of Minami-Iwo-jima.
Water discolor is frequently observed from the volcano, and several ephemeral islands have formed in the 20th century.
The first of these formed Shin-Iwo-jima ("New Sulfur Island") in 1904, and the most recent island was formed in 1986.
Fukutoku-Okanoba is part of an elongated edifice with two major topographic highs trending NNW-SSE
and is a trachyandesitic volcano geochemically similar to Iwo-jima.

Map showing Japan and the Volcano Island chain.
Volcanoes active in 1978 or 1979 are indicated by black squares.

Courtesy of JMA

February 2010
The February 2010 eruption was discovered at about 0745 by the Japan Coast Guard patrol boat Yashima on a routine
survey. The crew first noticed "smoke" coming from the surface of the ocean ~ 5 km NNE of the island of Minami-Iwo-
jima. The crew also heard a blast and felt its pressure wave. Smoke and ash rose roughly 30 stories into the air.
There had been no warning that an eruption was imminent.

Coast Guard vessels and aircraft are now collecting data in the area. It is very dangerous to approach the area as it is
impossible to predict further eruptions.

JMA isssued eruption alerts for 9 March and 8 April 2010. This suggests that the eruption continued into April.

Satellite image taken 11 February 2010 of the ocean around Fukutoku-Okanoba volcano.
The water colored by the plume forms a V-shape W of the volcano summit.

This true-color image was taken by the Advanced Land Imager (ALI) on NASA's EO-1 satellite.
Courtesy of NASA Earth Observatory.

Smoke and ash rise roughly 30 stories into the air in this image captured by a Japan Coast
Guard helicopter on February 3, 2010.

Photograph courtesy Japan Coast Guard

During a lull in the Fukutoku-Okanoba eruption on February 3, some of the waters above the
undersea volcano bubble and take on yellowish green colors, while others are cloudy with
displaced sand and grit.
Photograph courtesy Japan Coast Guard

July 2005.
JMA reported that at about 1745 on 2 July 2005, a white plume was witnessed at Fukutoku-Okanoba. During an investigation at 1900 that same day, a white plume reached ~ 1 km above the sea surface. A photo taken from considerable distance was included in the JMA report, showing the plume, but the image's limited contrast has led to its exclusion here. In addition to the plume, other evidence for an eruption included debris on the sea surface. When seen on 2 July, the debris covered an area approximately 100 m wide and 300 m long

An aerial view of Fukutoku-Okanoba taken on 3 July 2005 as seen from the NE. Debris and discoloration extend from the arrow.
Courtesy of the Maritime Security and Safety Agency.

The Maritime Security and Safety Agency conducted an underwater topographical survey on 20-22 July 2005, the result of which was the discovery of two craters caused by the recent eruption. The results suggested that the topography just S of those craters was newly raised.

January 1986
On 18 January, fishermen observed a large white plume rising to more than 3 km altitude and lava being ejected to about
300 m height form the vicinity of the submarine volcano Fukutoku-Okanoba. The eruption was first evident on infrared
imagery from the Japanese GMS geostationary weather satellite on 18 January at 2100. Japan Maritime Self-Defense
Force personnel stationed on Iwo-Jima, about 50 km from Fukutoku-Okanoba, observed a 4-km eruption cloud the
next day at 1630. The Japan Maritime Safety Agency's survey ship Takuyo found a new island about 5 km NE of
Minami Iwo Jima (south Iwo Jima) the morning of 21 January. The new island, about 700 m long and 300 m wide,
extended about 15 m above sea level. Lava was being ejected to about 300 m height.
As of 21 January, floating pumice had drifted 60 km to the SE.

Photograph of the new island and eruption plume at Fukutoku-Okanoba on 21 January 1986
at about 1400. The conical island in the right background is Minami-Iwo-jima.

Photo by G. Iwashita, JMA.

By 18 January at 2000, eruptive activity was frequent, producing a dark plume, seen from a fishing boat, that reached 3,000-4,000 m height. An hour later the plume was evident on an image from Japan's GMS satellite. The next day at about 1630, airborne radar detected a plume rising to 4,000 m above sea level. On 20 January at 0440, radar on the JMSA's survey ship Takuyo showed an island-like image. A gray plume rose to 2,000 m altitude at 0550.

Photograph of the new island and eruption plume at Fukutoku-Okanoba
on 21 January 1986 at about 1600.

Photo by G. Iwashita, JMA.

A new island was recognized by observers on the Takuyo at 0630. A 50-m vent at the NW edge of the new island
ejected plumes and sea water. Continuous observations were made until about 1000. The island was ~700 m long,
500 m wide, and 15 m high (figure 2). A vent near its E edge remained below sea level, ejecting black incandescent
rocks as much as 10 m in diameter. Grayish brown pumice had drifted as much as 18 km NE from the vent.
Discolored sea water surrounded the island and extended 22 km NE from the vent.
The sea water was greenish near the island, gradually becoming greenish yellow or pale blue farther from the vent.

The island formed 20 January . . . has been eroded away by wave action since volcanic activity ceased. The island's disappearance was reported by the JMSDF after an hour-long helicopter flight that began 8 March at 0745. The surface of the new edifice was seen under white water, and there was no sign of a volcanic plume.

On 28 January, airplane pilots observed light brown floating pumice within a roughly rectangular NW-SE-trending zone ~200 km long by 50 km wide, extending from ~100 to 300 km SE of the volcano. The pumice was in subparallel teardrop-shaped rafts roughly 4 km wide and 10 km long, elongate perpendicular to the apparent direction of drift.

March 25, 1975
A U.S. Air Force reconnaissance flight operating out of Guam sighted an area of oceanic volcanic
activity 32 km S of Iwo Jima. The sighting was described as possibly an island in the formative stages.



over 250


over 500


over 300

    alfabetisk liste
    alphabetic list

Denne siden er laget ved hjelp av Macromedia Dreamweaver