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Report on Sumisujima (Japan) — October 1992


Bulletin of the Global Volcanism Network, vol. 17, no. 10 (October 1992)
Managing Editor: Lindsay McClelland.

Sumisujima (Japan) Small zone of discolored water

Please cite this report as:

Global Volcanism Program, 1992. Report on Sumisujima (Japan) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 17:10. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199210-284080



31.44°N, 140.051°E; summit elev. 136 m

All times are local (unless otherwise noted)

A zone of discolored yellowish water 30 m [wide] and [6 km long] was observed by fishing crews at around 1100 on 7 October. A JMSA overflight on 9 October showed no anomaly. The volcano last erupted in 1916, ejecting tephra. Discoloration was seen at the shore and near the island in 1975, 1976, 1977, 1989, and August 1992.

Geological Summary. Sumisujima (also known as Smith Rocks) is a steep-sided basaltic pinnacle that forms part of the outer southern flank of a 8-9 km wide submarine caldera that truncates a 20-km-wide seamount. The caldera was formed between about 60,000 and 30,000 years ago. The Shirane dacitic central cone, 3 km wide and 800 m high, rises to within 8 m of the ocean surface in the eastern side of the caldera, whose 600-700 m walls and outer flanks expose basaltic, andesitic, and rhyolitic rocks. Two large submarine cones, Sumisu Knolls No. 1 and 2, lie west of the caldera. Submarine eruptions have been reported from a number of locations near Sumisujima, the last of which occurred in 1916. Water discoloration has frequently been observed since the 1970's. In October 1992 a 6-km-long zone of discolored water was seen extending from the shallow Shirane rock mass near the eastern rim of the caldera, which rises to within 7 m of the ocean surface and is the youngest feature of the volcanic complex.

Information Contacts: JMA; JMSA.