Report on Izu-Oshima (Japan) — October 1987
Scientific Event Alert Network Bulletin, vol. 12, no. 10 (October 1987)
Managing Editor: Lindsay McClelland.
Izu-Oshima (Japan) Renewed explosions; ash to 2,500 m; tourists evacuated
Please cite this report as:
Global Volcanism Program, 1987. Report on Izu-Oshima (Japan) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 12:10. Smithsonian Institution.
34.724°N, 139.394°E; summit elev. 758 m
All times are local (unless otherwise noted)
On 16 November at 1047 an eruption began with two explosions that sent a black ash and gas column to at least 2,500 m above the summit. Small eruptions continued every 5-10 minutes. Roads leading to the mountain were closed and about 150 tourists and others in the summit area were evacuated to a hotel on the N side of the crater at 1100. Heavy ashfall occurred on the S part of the island and more than 30 volcanic clasts fell near a shrine on the crater rim causing several small fires. A window was broken at a tea house near the crater but there were no reports of casualties or major damage. JMA recorded >1,000 small earthquakes before the eruption, and weak earthquakes continued afterwards. During an earthquake swarm in early October [12:9] the maximum daily number of recorded earthquakes reached twice the previous maximum for 1987.
The JMSA and the Japan Maritime Self-Defense Force (JMSDF) mobilized patrol boats and escort vessels off the island.
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: A. Izumo, Yokohama Science Center; Japan Times, Tokyo; UPI.