No water discoloration seen in 1990

No discolorations were observed at . . . Kaitoku . . . during 1990.

Information Contacts: Hydrographic Department, JMSA.

Information is preliminary and subject to change. All times are local (unless otherwise noted)

February 1984 (SEAN 09:02) Cite this Report

Large area of discolored water; small plumes

On 7 March at 1230, the crew of a Japan Maritime Self-Defense Force (JMSDF) transport plane flying about 130 km N of Iwo-Jima observed a fan-shaped zone of discolored sea water that extended about [28] km WSW from a submarine vent. The maximum width of the discolored zone was about 9 km. A helicopter flew over the area shortly thereafter and its crew estimated that the extent of the reddish-brown water was roughly as large as Iwo Jima Island (about 5 x 8 km).

The next morning, JMSA personnel observed continuous submarine eruptive activity. Gray or yellowish brown water was ejected every 10 minutes and waves spread outward from the vents. The sea colors included gray, white, yellowish brown, and reddish brown. JMSA observers saw neither plumes nor floating ejecta, although small white plumes and rocks or reefs were seen during a flight by the JMSDF at about noon the same day. On 12 March, personnel aboard a JMSDF patrol plane again saw floating material, and a plume about 100 m above sea level. Only discoloration was found during a JMSA flight 13 March. As of the 13th, no new island had been observed at the eruption site.

The activity was located near the site of an eruption reported in 1543 at 26.00°N, 140.77°E.

Information Contacts: JMA.

April 1984 (SEAN 09:04) Cite this Report

Acoustic waves recorded in French Polynesia

RSP stations on Rangiroa, Tubuai, and Rikitéa recorded acoustic waves (T-phase) from a strong submarine volcanic eruption in the vicinity of the Izu Islands. Between 25 March and 30 April, more than 500 signals were received, 300 between 2 and 9 April. Most of the events were impulsive and of short duration, indicating explosive volcanic activity at a shallow depth. Some of the events were emergent and of longer duration indicating quiet emission of lava. J.M. Talandier noted that these events appear to be correlated with the submarine activity reported in 9:2.

Information Contacts: J. Talandier, Lab. de Géophysique, Tahiti.

May 1984 (SEAN 09:05) Cite this Report

Discolored water; floating lapilli; formal name

JMSA observations beginning 7 March indicated that eruptive activity was at its highest level in mid to late March, when floating ejecta and vapor plumes were nearly always seen. Beginning in April, activity subsided gradually. The area of discolored water decreased from 13 x 30 km in early March to 300 m in diameter in early May (table 1).

On either side of the submarine vent are two shallow areas, at 26.13°N, 141.10°E, and 26.05°N, 140.93°E (figure 1). JMSA has formally named the feature Kaitoku Kaizan (Kaitoku Seamount).

Figure 1. Cross-section (top) and bathymetry (bottom) at Kaitoku Seamount. Courtesy of JMSA.

Information Contacts: JMA, Tokyo.

October 1984 (SEAN 09:10) Cite this Report

Discolored water after 3 months of quiet

JMSA reconnaissance revealed few signs of activity since the March eruption. Pumice was observed only around the eruption site; none washed up on shore.

Activity gradually declined. To the crew that overflew the area at noon on 9 April, the water discoloration was barely distinguishable, and no ejecta or plume was seen (table 1). JMSA and JMSDF saw no discolored water or other activity on 10 and 31 July, 1 August, and 6 and 26 September. However, the crew of the MV Emblem reported a 3.5-5-km area of upwelling and water discoloration on 15 October.

Table 1. JMSA observations at Kaitoku Seamount, March-June 1984. Courtesy of JMA.

Further Reference. Tsuchide, M., Kato, S., Uchida, A., Sato, H., Konishi, N., Osaka, J., and Hirabayashi, J., 1985, Submarine volcanic activity at the Kaitoku seamount in 1984: Rep. Hydrograph. Res., v. 20, p. 47-82.

Information Contacts: JMA, Tokyo.

December 1990 (BGVN 15:12) Cite this Report

No water discoloration seen in 1990

No discolorations were observed at . . . Kaitoku . . . during 1990.

Information Contacts: Hydrographic Department, JMSA.