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Report on Kozushima (Japan) — September 1992


Bulletin of the Global Volcanism Network, vol. 17, no. 9 (September 1992)
Managing Editor: Lindsay McClelland.

Kozushima (Japan) Weak earthquake swarm

Please cite this report as:

Global Volcanism Program, 1992. Report on Kozushima (Japan) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 17:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199209-284030



34.219°N, 139.153°E; summit elev. 572 m

All times are local (unless otherwise noted)

A weak earthquake swarm occurred 5 km W of the island on 1 September. Maximum magnitude was 2.1. No surface activity was evident on the island or in the sea.

Geological Summary. A cluster of rhyolitic lava domes and associated pyroclastic deposits form the 4 x 6 km island of Kozushima in the northern Izu Islands. The island is the exposed summit of a larger submarine edifice more than 20 km long that lies along the Zenisu Ridge, one of several en-echelon ridges oriented NE-SW, transverse to the trend of the northern Izu arc. The youngest and largest of the 18 lava domes, Tenjosan, occupies the central portion of the island. Most of the older domes, some of which are Holocene in age, flank Tenjosan to the north, although late-Pleistocene domes are also found at the southern end of the island. A lava flow may have reached the sea during an eruption in 832 CE. The Tenjosan dome was formed during a major eruption in 838 CE that also produced pyroclastic flows and surges. Earthquake swarms took place during the 20th century.

Information Contacts: JMA.