Report on Kozushima (Japan) — August 1993
Bulletin of the Global Volcanism Network, vol. 18, no. 8 (August 1993)
Managing Editor: Edward Venzke.
Kozushima (Japan) Earthquake swarms
Please cite this report as:
Global Volcanism Program, 1993. Report on Kozushima (Japan) (Venzke, E., ed.). Bulletin of the Global Volcanism Network, 18:8. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199308-284030.
34.219°N, 139.153°E; summit elev. 572 m
All times are local (unless otherwise noted)
An earthquake swarm near and below Kozu-shima island occurred on 9-10 August, with 12 shocks felt on the island, the largest M 3.3. Another earthquake near the island, M 3.7, occurred in the early morning on 22 August.
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.