昭和27年9月の明神礁噴火活動について

抄録

A new volcanic isle near the Bayonnaise Rocks, 450km south of Tokyo was discovered by the crew of a Japanese fishing boat, the No. 11 Myojin Maru, on Sept. 17, 1952. The exact location of the new volcanic isle was given by the stuff of oceanography, Tokyo Fisheries University, at 31°56′. 8N. and 139°59′. 5E. and it belongs to Fuji volcanic belt. According to newspapers, the pyroxysmal eruption as well as lava effusion were observed and the radius of the newly-extruded lava isle was 100-150 meters. Also it was reported that since Sept. 21, intermittent severe explosions were observed. On Sept. 23, by the courtesy of Tokyo Fisheries University we could approach the isle and observed explosios five times in one day on board the Shin' yo Maru, a 230-ton training ship of the University. The newly-formed isle had already disappeared under the sea but we could find the position of the undersea crater because the sea water, there, was remarkably yellowish. On the following day, Sept. 24, the No. 5 Kaiyo Maru, a 211-ton oceanographical survey boat of the Maritime Safety Board was missing near the new undersea volcano and all 31 on the ship, including a crew of 22 and nine experts on geology and oceanography were believed to have met tragic end. It was reported afterwards by a survey ship of MSB that a volcanic isle, 300-400m width, was pushed up again and steamed white vapour. The newly-ejectd pumice is quartz-andesitic. The energy of one explosion, occurred on Sept. 23, was estimated to be about 10¹⁸ erg. by the writer.