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Bayonnaise Rocks volcanoBayonnaise Rocks volcano (ベヨネース列岩 Beyonēsu-retsugan) is an active submarine volcano in the Izu Islands ca. 400 km south of Tokyo. The volcano has a large 8-9 km wide caldera whose highest point forms a few rocks rising just above sea level. The volcano is known for its submarine eruptions which sometimes produce temporary islands.
Most of its frequent eruptions have occurred at Myojin-sho, a large young lava dome on the NE rim of the caldera. In 1952, an explosive eruption at Myojin-sho destroyed a Japanese research vessel, killing all 31 people on board.
There is only sparse vegetation on the Bayonnaise Rocks, but the islands are an important resting place for migratory birds. Located in the Kuroshio Current, the waters around have abundant sea life and are popular with sports fishermen.
Background:The formation of the Bayonnaise Rocks caldera was followed by construction of a large (2.6 km3) lava dome and/or lava complex of lava flows on the caldera floor, which was originally at a depth of 1000-1100 m.
Bayonnaise Rocks has deposits from submarine pyroclastic flows which are the result of the growth of the dacitic lava dome. These deposits mantle the conical dome and extend into the NE part of the caldera and down its outer slopes.
(Source: Smithsonian / GVP volcano information)
1952-53 eruption and Kaiyo-maru no. 5 disaster
The eruption of Myozin-sho in 1951-54 (Bayonnaise rocks volcano) was one the most notable eruption in Japan during the 1950s.
The first report of a new submarine eruption was on 17 September 1952 by a crew of the fishing boat Myozin-maru No. 11. The site of the eruption was the Myozin-sho lava dome at the NE end of Bayonnaise Rocks. The activity quickly formed a temporary island 150 m long, 100 m wide and 30 m high. The island was eroded and disappeared again by 23 September. An explosive eruption produced a 2 m high tsumani on 24 September.
The Kaiyo-maru No. 5 disaster:
Kaiyo-maru No. 5 was a Japanese research vessel for marine observation from the Hydrographic Office of the Maritime Safety Board in Japan. The ship sailed from Tokyo on 23 September 1952 to survey the submarine topography in the vicinity of the eruption.
The exact circumstances being unknown, the ship must have capsized and sunk quickly when it was at close range of a submarine explosive eruption 12h30 local time on 24 September 1952. All men on board (31) including 9 scientists were lost and there were no eye-witnesses to the tragedy. A tide gauge at Hatizyo-sima Weather Station, 120 km north Myozin-syo, recorded a 2 m high passing tsunami at 12h53 m, ca 25 minutes after the explosion of the volcano. US Navy hydrophones on Hawaii measured underwater sounds from the explosions.
Later, wreckage of the Kaiyo-maru No. 5 was found drifting south of the volcano during 25-28 September. Pieces of fragmental lava and pumice from Myozin-sho volcano were found attached to to some parts of the wreckage, suggesting that the vessel was directly hit by powerful jets of water and tephra ejected during the explosion.
Takeshi Minakami (1956) "Report on volcanic activities and volcanological studies in Japan for the period from 1951 to 1954", Bull. Volc., Volume 18 (1), pp. 39-76
A submarine eruption from Bayonnaise Rocks occurred between 7-13 April 1906. Large amounts of pumice were found floating on the sea.