Renewed activity at September site

An ocean bottom seismometer off the Boso Peninsula, Japan, and hydrophones on Wake Island detected renewed episodes of apparent submarine volcanism on 22-24 and 26-27 December. Arrival directions and times were very similar to those from the 21-22 September activity, and probably originated from the same area.

Seismicity began to be recorded by the Boso Peninsula instrument on 22 December at about 0630, and events soon became frequent, although intervals between events were slightly longer than in September. Seismicity had nearly ended shortly before 0200 on 24 December, although one additional shock was recorded at 0245. T-phase signals resumed on 26 December at about 1600 and continued until about 2300 the next day, but occurred at significantly longer intervals than the two earlier episodes.

Using more precise sound velocities, Univ of Hawaii geophysicists refined the locations of the 21-22 September events to about 20.3°N, 144.9°E, roughly 30 km S of . . . Farallon de Pajaros (Uracas). The potential location error remains large, but is oriented along a NE-SW line oblique to the volcanic chain. The 21-22 September locations are very close to the site of the most recent documented activity near Farallon de Pajaros, a 3-km zone of discolored water that was observed in September 1985 near the 1969 eruption site.

Information Contacts: Y. Sawada, JMA; C. McCreery and D. Walker, Univ of Hawaii.

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

May 1969 (CSLP 43-69)

Submarine eruption during 11-12 March

Card 0528 (06 May 1969) Acoustic activity during 11-12 March

The following was received in a telephone report from Tom Simkin (Smithsonian Institution). "Examination of government recordings made at Eniwetok, Wake, and Midway hydrophone stations turned up acoustic activity which appears to be at the location of the March 1967 event (Norris and Johnson, 1969) near Farallon de Parajos in the Northern Mariana Islands [but see next report for better location placing this event just NW of Supply Reef]. The recent activity occurred at a fairly uniform rate for two days beginning 11 March 0100 GMT and ending 12 March 2300 GMT, 1969."

Reference. Norris, R.A., and Johnson, R.H., 1969, Submarine volcanic eruptions recently located in the Pacific by Sofar hydrophones: Journal of Geophysical Research, v. 74, no. 2, p. 650-664.

Card 0534 (08 May 1969) Explosions sounds and water discoloration

The following cable was received from the Japanese Meteorological Agency. "Fishing boat sailing near Uracas Island in Marianas informed of submarine eruption as follows: From about 0930 GMT on 12 March explosion sounds - three times - were heard in latitude 20.24°N, longitude 145.02°E, neighboring sea surface was colored in brown."

Information Contacts:
Card 0528 (06 May 1969) Roger A. Norris, The T-Phase Project, University of Hawaii, Honolulu, Hawaii.
Card 0534 (08 May 1969) Seismological Section, Japanese Meteorological Agency.

September 1985 (SEAN 10:09) Cite this Report

Discolored water but no eruption plume

On 2 September, a Continental Air Micronesia pilot observed a zone of brown and light green discolored water about 3 km in diameter, centered about 30 km S of Farallon de Pajaros. No eruption plume was seen by the pilot and inspection of satellite images for several days after 2 September revealed no visible plumes. Cloudy weather obscured the area in the days immediately preceding 2 September. No other reports of activity have been received.

The location of the 1985 activity is approximate, but is not inconsistent with the position of the 1969 eruption and the seamount.

Information Contacts: N. Banks, CVO, Vancouver, WA; W. Gould, NOAA/NESDIS.

November 1985 (SEAN 10:11) Cite this Report

T-Phases recorded in Tahiti may be from this site

Between 2 August and 5 September, 109 T-phase events originating in the NW Pacific were received by a high-gain station at Rangiroa, Tahiti. J.M. Talandier notes that their characteristics are typical of submarine volcanic eruptions, being of shallow (ocean) depth; the timing of the events coincides with the presence of a zone of discolored water near [Supply Reef]. However, a precise origin cannot be determined because the events were of weak amplitude and recorded by only one station.

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

October 1989 (SEAN 14:10) Cite this Report

Twenty-one hours of volcanic seismicity

An intense episode of apparent submarine volcanism was recorded 21-22 September by an 11-channel hydrophone array on Wake Island, an ocean bottom seismometer off Japan's Boso Peninsula, and the Polynesian Seismic Network's Pomariorio station, on Rangiroa atoll. Strong activity began at about 1100 and peaked between 1230 and 1520, with several hundred distinct events detected before the episode ended abruptly at about 0755 the next morning. During the activity, continuous noise levels in the SOFAR channel remained at least 20 dB above normal ambient values, at frequencies of 5-30 Hz. T-Phase arrivals at the three sites were used to determine a rough location for the activity at 21.9°N, 145.9°E, with a typical potential error of about ± 100 km [but see 14:12]. However, the calculated position is displaced >200 km E of the northern Marianas volcanic arc, falling on the W edge of the trench.

The nearest known submarine volcanic site is . . . Farallon de Pajaros (Uracas) at 20.53°N, 144.90°E. Activity was last reported from the area on 2 September 1985, when a 3-km zone of discolored water near the 1969 eruption site (about 30 km S of Farallon de Pajaros) was observed from an aircraft. Between 2 August and 5 September 1985, the Polynesian Seismic Network's Rangiroa station recorded 109 T-Phase events, with characteristics typical of submarine eruptions, originating from the NW Pacific. However, no other seismic stations were known to have recorded the activity and a precise location was impossible.

Reference. McCreery, C., Oliveria, F., and Walker, D., 1989, Submarine volcano: EOS, v. 70, p. 1466.

Information Contacts: D. Walker, Univ of Hawaii; J. Talandier, LDG, Tahiti; Y. Sawada, JMA.

December 1989 (SEAN 14:12) Cite this Report

Renewed activity at September site

An ocean bottom seismometer off the Boso Peninsula, Japan, and hydrophones on Wake Island detected renewed episodes of apparent submarine volcanism on 22-24 and 26-27 December. Arrival directions and times were very similar to those from the 21-22 September activity, and probably originated from the same area.

Seismicity began to be recorded by the Boso Peninsula instrument on 22 December at about 0630, and events soon became frequent, although intervals between events were slightly longer than in September. Seismicity had nearly ended shortly before 0200 on 24 December, although one additional shock was recorded at 0245. T-phase signals resumed on 26 December at about 1600 and continued until about 2300 the next day, but occurred at significantly longer intervals than the two earlier episodes.

Using more precise sound velocities, Univ of Hawaii geophysicists refined the locations of the 21-22 September events to about 20.3°N, 144.9°E, roughly 30 km S of . . . Farallon de Pajaros (Uracas). The potential location error remains large, but is oriented along a NE-SW line oblique to the volcanic chain. The 21-22 September locations are very close to the site of the most recent documented activity near Farallon de Pajaros, a 3-km zone of discolored water that was observed in September 1985 near the 1969 eruption site.

Information Contacts: Y. Sawada, JMA; C. McCreery and D. Walker, Univ of Hawaii.