Report on Izu-Oshima (Japan) — July 1987
Scientific Event Alert Network Bulletin, vol. 12, no. 7 (July 1987)
Managing Editor: Lindsay McClelland.
Izu-Oshima (Japan) Volcanic tremor; small earthquakes below summit
Please cite this report as:
Global Volcanism Program, 1987. Report on Izu-Oshima (Japan). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 12:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198707-284010.
34.724°N, 139.394°E; summit elev. 758 m
All times are local (unless otherwise noted)
Intermittent volcanic tremor occurred during July. Durations of tremor episodes generally ranged from a few minutes to 2 hours but episodes lasting more than 10 hours were sometimes recorded. Small earthquakes with foci under the summit area were registered at a rate of ~40/day by the seismograph N of the summit caldera. A steam plume rose continuously to ~50 m above the summit crater.
Geologic Background. Izu-Oshima volcano in Sagami Bay, east of the Izu Peninsula, is the northernmost of the Izu Islands. The broad, low stratovolcano forms an 11 x 13 km island and was constructed over the remnants of three dissected stratovolcanoes. It is capped by a 4-km-wide caldera with a central cone, Miharayama, that has been the site of numerous historical eruptions. More than 40 cones are located within the caldera and along two parallel rift zones trending NNW-SSE. Although it is a dominantly basaltic volcano, strong explosive activity has occurred at intervals of 100-150 years throughout the past few thousand years. Historical activity dates back to the 7th century CE. A major eruption in 1986 produced spectacular lava fountains up to 1600 m height and a 16-km-high eruption column; more than 12,000 people were evacuated from the island.
Information Contacts: JMA.