Report on Ioto (Japan) — 27 July-2 August 2022
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
27 July-2 August 2022
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2022. Report on Ioto (Japan). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 27 July-2 August 2022. Smithsonian Institution and US Geological Survey.
24.751°N, 141.289°E; summit elev. 169 m
All times are local (unless otherwise noted)
Satellite images of Ioto (Iwo-jima) acquired on 15 July showed a darker area in the water along the SE coast, possibly above or near the 2001 vent, and a plume of discolored water drifting NE. Video taken on or around 25 July showed a white plume rising from the same area. Satellite images during 30-31 July showed small rounded gray zones at the water surface.
Geological Summary. Ioto in the central Volcano Islands portion of the Izu-Marianas arc lies within a 9-km-wide submarine caldera. Ioto, Iwojima, 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.