New island emerges near Iwo Jima in Ogasawara chain, Japan

On November 1, 2023, military personnel located on Iwoto Island witnessed the birth of a new island following intense volcanic activity. The eruption, which occurred 1 km (0.62 miles) off the island’s southern coast, was preceded by frequent volcanic tremors since October 21.

An undersea volcanic eruption has led to the creation of a new island within the Ogasawara island chain, situated more than 1 000 kilometers (620 miles) to the south of Tokyo. This natural occurrence was confirmed by the Maritime Self-Defense Force’s (MSDF) base on the nearby Iwoto (Ioto) island, historically known as Iwo Jima, on November 1.

The personnel at the MSDF base were alerted to the event by significant noise and the sight of soil and debris being propelled into the sky.

According to the Global Volcanism Program, the eruption that created it occurred at a vent located about 1 km (0.6 miles) off the coast of Okinahama, on the SE side of the island. During an overflight on October 30, observers recorded explosions every few minutes that ejected dark material about 20 m (65 feet) above the surface of the ocean. Ejecta from the vent built a black-colored island and floating pumice was present around the island.

A satellite image acquired by Sentinel-2 on November 2 shows the island is approximately 230 m (754 feet) long and 200 m (656 feet) wide:

The Japan Meteorological Agency (JMA) has been monitoring the area and reported persistent volcanic tremors on Iwoto island, occurring at intervals of a few minutes, since approximately October 21. These tremors culminated in the underwater eruptions that have now resulted in the formation of new land.

Situated close to the undersea volcano’s crater, the nascent island was formed as a consequence of the accumulated rocks and ejected material from the ocean floor. The JMA has suggested that the considerable ejection of rocks and stones from the crater contributed to the accumulation that formed the islet.

The creation of the island follows a pattern of geological change in the region, as Iwoto island itself has been experiencing a rise in elevation attributed to ongoing volcanic activity. Earlier in June, pumice stones, believed to be from the same volcanic activity, were found floating in the waters near the island, signaling the dynamic nature of the earth’s geological processes in the area.

Ioto, forming part of the central Volcano Islands within the Izu-Bonin-Mariana arc, is encircled by a submarine caldera measuring 9 km (5.59 miles) in width. The island is known by various names, including Iwojima and Iojima, amongst other transliterations. To avoid confusion with other volcanoes nicknamed “Sulfur Island” in Japan, it is also referred to as Ogasawara-Iojima. This triangular island, which stretches over a length of 8 km (4.97 miles) and tapers towards its southwestern tip, is characterized by its low elevation and has a geological composition of trachyandesitic and trachytic rocks. These rocks are notably more alkalic compared to those from other volcanoes along the same volcanic arc.

For more than 700 years, Ioto has been experiencing a consistent uplift, an event accompanying the resurgent doming of the submerged caldera. Evidence of this uplift is clear when considering that a shoreline once surveyed by Captain Cook’s crew in 1779 is now positioned 40 meters (131 feet) above the current sea level. The Motoyama plateau on the northeastern section of the island is notably composed of submarine tuffs topped with coral deposits, establishing the highest elevation point on the island. A significant number of fumaroles, which align along a northeast-southwest axis that bisects Motoyama, are a testament to the island’s active geothermal nature.

Historical accounts have noted numerous phreatic eruptions, particularly from vents located on the western and northwestern segments of the island, which have been a consistent accompaniment to the geological uplift over the centuries.​

Uno dei primi video dell'eruzione surtseyana (🌊 + 🌋) in corso al largo dell'isola di #IwoJima, in Giappone. L'accumulo e il consolidamento del materiale espulso dall'attività esplosiva ha già formato un'isola lunga più di 200 metri. È l'isola più giovane del nostro pianeta! pic.twitter.com/KcQe2eDRkP

— Il Mondo dei Terremoti (@mondoterremoti) November 5, 2023

References:

¹ New isle emerges in Ogasawara chain after volcano erupts – The Asahi Shimbun – November 3, 2023

² Global Volcanism Program, 2023. Report on Ioto (Japan) (Sennert, S, ed.). Weekly Volcanic Activity Report, 25 October-31 October 2023. Smithsonian Institution and US Geological Survey

³ Ioto – Geological summary – GVP

Featured image: Satellite image of a new island near Iwo Jima on November 2, 2023. Credit: Copernicus EU/Sentinel-2, EO Browser, The Watchers