Report on Ioto (Japan) — April 1983
Scientific Event Alert Network Bulletin, vol. 8, no. 4 (April 1983)
Managing Editor: Lindsay McClelland.
Ioto (Japan) Earthquake swarm, two weak steam explosions
Please cite this report as:
Global Volcanism Program, 1983. Report on Ioto (Japan) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 8:4. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198304-284120.
24.751°N, 141.289°E; summit elev. 169 m
All times are local (unless otherwise noted)
The National Research Center for Disaster Prevention reported that two weak steam explosions from Asodai Crater 28-29 November 1982 were associated with an earthquake swarm 25-30 November. Among the 1,492 recorded seismic events were 13 felt shocks. Before the swarm, the maximum number of recorded seismic events for a 5-day period had been 104. The earthquakes cracked roads in some places.
Geologic Background. Ioto (changed from Iwo-jima in 2007) in the central Volcano Islands portion of the Izu-Marianas arc lies within a 9-km-wide submarine caldera. Ioto, Iwo-jima, and Iojima are among many transliterations of the name. The volcano is also known as Ogasawara-Iojima to distinguish it from several other "Sulfur Island" volcanoes in Japan. The triangular, low-elevation, 8-km-long island narrows toward its SW tip and has produced trachyandesitic and trachytic rocks that are more alkalic than those of other Izu-Marianas arc volcanoes. The island has undergone dramatic uplift for at least the past 700 years accompanying resurgent doming of the caldera. A shoreline landed upon by Captain Cook's surveying crew in 1779 is now 40 m above sea level. The Motoyama plateau on the NE half of the island consists of submarine tuffs overlain by coral deposits and forms the island's high point. Many fumaroles are oriented along a NE-SW zone cutting through Motoyama. Numerous historical phreatic eruptions, many from vents on the west and NW sides of the island, have accompanied the remarkable uplift.
Information Contacts: JMA.