Report on Ioto (Japan) — 17 October-23 October 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 17 October-23 October 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2001. Report on Ioto (Japan). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 17 October-23 October 2001. Smithsonian Institution and US Geological Survey.
24.751°N, 141.289°E; summit elev. 169 m
All times are local (unless otherwise noted)
On the morning of 19 October a small phreatic eruption was observed at Idogahama, a beach on the NW coast of Iwo-jima. The Japan Maritime Self Defense Force observed a grayish white-colored plume rising to 200-300 m above the beach surface for 2-3 minutes starting at about 0725. A similar plume was observed for 10 minutes starting at 0806. Observations during 1602-1715 revealed the crater that formed during the eruption was 10 m long and 2-15 m deep. Water inside the crater was dark colored, contained debris, and gushed approximately every 10 minutes. In addition, a steam plume rose up to 600 m above the surface.
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.