Environment

Undersea eruption detected at Ioto (Iwo Jima), seawater shooting as high as 10 m (33 feet), Japan


Aerial photos taken on Wednesday, September 12, 2018, show sure signs of undersea volcanic eruption at Japanese Ioto volcano, former Iwo Jima. The volcano has been showing increased volcanic activity since the past weekend.

JMA said Wednesday that photos taken by navy aircraft showed seawater shooting as high as 10 m (33 feet) above the surface just off the southern coast of Ioto.

Defense officials said troops stationed on the island are safe and there are no evacuation plans.

In just two days, Ioto saw 10 cm (3.93 inches) of uplift, the Geographical Survey Institute of Japan said in the monthly report of geodetic changes in Japan released September 11.

The last known eruption of this volcano took place in 2012. Its previous eruptions took place in 2004, 2001, 1994 and 1982. All of them had Volcanic Explosivity Index of 1.

Geological summary

Ioto (changed from Iwo-jima in 2007) in the central Volcano Islands portion of the Izu-Marianas arc lies within a 9-km-wide (5.6 miles) 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 (5 miles) 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 (131 feet) 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.

Featured image credit: Tatsu Kawasaki, September 8, 2018. (Instagram)


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