Report on Kozushima (Japan) — May 1992
Bulletin of the Global Volcanism Network, vol. 17, no. 5 (May 1992)
Managing Editor: Lindsay McClelland.
Kozushima (Japan) Continued seismic swarms
Please cite this report as:
Global Volcanism Program, 1992. Report on Kozushima (Japan) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 17:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199205-284030.
34.219°N, 139.153°E; summit elev. 572 m
All times are local (unless otherwise noted)
Abnormal seismicity continued around the volcano in May, when 2 earthquake swarms were recorded. On 8 May a swarm occurred 2-3 km E of the island, with M <3.9. The second, on 14-16 May, occurred 3-4 km NW, with the largest event (M 4.9) recorded at 0731 on 15 May. No surface anomalies were observed.
Geologic Background. A cluster of rhyolitic lava domes and associated pyroclastic deposits form the small 4 x 6 km island of Kozushima in the northern Izu Islands. Kozushima 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, 574-m-high Tenjoyama, occupies the central portion of the island. Most of the older domes, some of which are Holocene in age, flank Tenjoyama to the north, although late-Pleistocene domes are also found at the southern end of the island. Only two possible historical eruptions, from the 9th century, are known. A lava flow may have reached the sea during an eruption in 832 CE. Tenjosan lava 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.