An episode of submarine volcanic activity in the northern Mariana Islands, in the northwest Pacific Ocean, has been recorded by the Wake Island hydrophone array. F. Oliveira, C. McCreery and D. Walker of the Hawaii Institute of Geophysics in Honolulu collected the data (see figure) while they were installing upgraded recording equipment for the array.
Intense activity began about 02 hours on September 21 UT and ended abruptly about 23 hours that day. During that time several hundred distinct events were observed. Continuous noise levels in the SOFAR channel were at least 20 dB above normal ambient noise levels at frequencies from 5 to 30 Hz. The location of the activity was about 21.9°N, 145.9°E. N. Hamada reported that it was recorded by ocean bottom seismometers of the Japan Meteorological Agency (JMA) sited off the east coast of Japan. The Polynesian Seismic Network also recorded the episode.