Abstract
A submarine volcano "Teisi Knoll " erupted in the western part of Sagami Bay, east of Izu Peninsula on July 13, 1989. Coincidentally, S/V "TAKUYO" of the Hydrographic Department of Japan was engaged in the survey in the area which was hit by a swarm of earthquake having become active since June 30, 1989, and encountered the eruption within the distance of 500 meters. We recorded the volcanic eruption by means of VTR, camera and tape recorders. The HD carried out seabottom surveys 3 times in total before and after the eruption, and has observed topographic change of sea bed birth of a submarine volcano. On July 9, S/V "MEIYO" observed flat sea floor 100 meters deep. While in the morning of July 13 S/V "TAKUYO" observed a cone-shaped height of 25 meters elevation on the floor. On July 15, S/V "SHOYO" observed Teisi Knoll with a crater ranging 200 meters in diameter by means of a radio controlled buoy "MANBOU"
