Report on Izu-Oshima (Japan) — December 1990
Bulletin of the Global Volcanism Network, vol. 15, no. 12 (December 1990)
Managing Editor: Lindsay McClelland.
Izu-Oshima (Japan) Decreased seismicity; continued steam emissions
Please cite this report as:
Global Volcanism Program, 1990. Report on Izu-Oshima (Japan) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 15:12. Smithsonian Institution.
34.724°N, 139.394°E; summit elev. 758 m
All times are local (unless otherwise noted)
Steady steam emission continued following the 4 October ash emission, reaching 1,000 m above the crater (figure 23). No additional eruptions from Mihara-yama cone had occurred as of 14 January 1991. A total of 57 earthquakes were recorded in December, down from 155 in November. No tremor episodes have been recorded since late April.
|Figure 23. Monthly mean estimated plume heights from Oshima, 1987-90. Arrows mark eruptions. Courtesy of JMA.|
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.