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Additional Reports

Reports are sometimes published that are not related to a Holocene volcano. These might include observations of a Pleistocene volcano, earthquake swarms, or floating pumice. Reports are also sometimes published in which the source of the activity is unknown or the report is determined to be false.

1986 Submarine Explosion

Kermadec Islands

24.43°S, 175.50°W

Index of Monthly Reports

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

10/1986 (SEAN 11:10) Violent underwater explosion reported

11/1986 (SEAN 11:11) Probably an earthquake in the Tonga Trench

Contents of Monthly Reports

All information contained in these reports is preliminary and subject to change.

All times are local (= UTC + 13 hours)

10/1986 (SEAN 11:10) Violent underwater explosion reported

On 11 November at 0710, the yacht Nutra, traveling from Rarotonga to Auckland, was shaken violently in what was described as an underwater explosion [but see 11:11]. Disturbed sea conditions preceded the main explosion.

The reported location is ~100 km E of the trend of the Tonga-Kermadec chain, over the W edge of the Tonga Trench at its S end; 570 km NNE of Raoul Island and 380 km S of Tongatapu. We are not aware of previous reports of activity in this area. The Worldwide Standardized Seismic Network recorded no nearby earthquakes at the time, although aftershocks of the M 8.2 Kermadec Islands event of 20 October continued 400 km to the S.

Information Contacts: J. Latter, DSIR Geophysics, Wellington; NEIC.

11/1986 (SEAN 11:11) Probably an earthquake in the Tonga Trench

The 11 November submarine explosion is now believed to have been an earthquake. To persons on board the yacht Nutra, the event sounded like a dynamite blast followed by a pair of echoes with a total duration of 1 second. Intensities of the blast and echoes were estimated by crewmen at 100, 90, and 80 decibels. No pumice, ash, or water discoloration were observed.

P and S waves, apparently from this event, were recorded at Rarotonga, Cook Islands, and Mangahao, New Zealand; local magnitude was about 4.5-5. The yacht's position at the time of the event, over the W side of the Tonga Trench, was determined by satellite navigation, accurate to within ~1.5 km.

Information Contacts: J. Latter, DSIR Geophysics Division, Wellington; P. Black, Univ of Auckland, Auckland.