Submarine volcanic eruption of Teisi knoll off eastern part of Izu Peninsula.
Since 1978, a series of frequent earthquake swarm have occurred at the sea east of Izu Peninsula, while Japan Meteorological Agency (JMA) observed 12 swarms for the period of 12 years up to 1989. The 12th earthquake swarm began on June 30, 1989. Seismic foci of the swarm were plotted in the sea only a few km north/ east of downtown Ito City and its coastal area. At about 18h 33m (JST) of July 13 1989, a submarine volcanic eruption spontaneously occurred at sea about 4 km northeast of downtown Ito. Japan Hydrographic Department (JHD) Survey Vessel TAKUYO was just around the point of the eruption and was surveying the seismic active area. TAKUYO was hit by frequent very strong shocks of water waves of the eruption at distances of 800m to few km from the newly born volcano. Surveyors and crew members of the vessel took photo, video tape record and audio record of the shock noise caused by the very strong water waves, while the positioning was done by GPS. Water mass gushing phenomena (water dome and/ or water jet) occurred five times, and the top of the biggest one was measured 113 m high above sea. Estimated time of beginning of the water mass gushing phenomena were 18 h 35 m 57 s, 18 h 39 m 57 s, 18 h 40 m 40 s, 18 h 41 m 25 s and 18 h 43 m 37 s of July 13 1989. HDJ conducted sea bottom surveys of the area four times. On July 9, a echo sounder and a side scan sonar of S/V MEIYO confirmed sedimented flat bottom at and around the forthcoming eruption point. At 18 h 28 m of July 13, or only 5 minutes before the eruption, S/V TAKUYO found a knoll of 25 m relative height, of about 500 m diameter at the base. JMA observed very large amplitude tremor from July 11 through July 13 without any remarkable surface phenomena, which suggest shallow magmatic intrusion beneath the knoll. On July 15, or two days after the eruption, unmanned automated survey craft MANBOU surveyed the knoll and found an about 200 m diameter crater in the center of the knoll, which reduced height of the knoll to only 10 m. MANBOU’s echo sounder recorded a big vertical cloud of volcanic gas welling up from the crater. On October 16 and 17, S/V TENYO surveyed the details of the newly born volcano (the knoll) and the vicinity with her narrow multi beam echo sounder (Hydrochart). The result shows shallowest water depth 81 m of the knoll on its southeast part of the crater rim, and deepest water depth 122 m at the southern part of the crater.
| Main Authors: | , , , , |
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| Format: | Journal Contribution biblioteca |
| Language: | Japanese |
| Published: |
1990
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| Online Access: | http://hdl.handle.net/1834/16067 |
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