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Japan gets a new island after undersea volcano erupts

Japan has gained another island to add to its already impressive collection, after an undersea volcanic eruption 1,200km (745 miles) south of Tokyo created a new landmass.

Experts said the tiny island emerged after a series of eruptions that began in October near Iwoto island, part of the Ogasawara island chain in the western Pacific.

Fukashi Maeno, an associate professor at Tokyo University’s earthquake research institute, said he had confirmed that phreatomagmatic eruptions – a type of explosive eruption that results from magma interacting with water – had occurred about a kilometre off Iwoto, forming a landmass of about 100 metres in diameter.

Maeno, who flew over the site at the end of October, told the Kyodo news agency that plumes of smoke and ash of more than 50 metres high rose every few minutes during the eruptions.

Related: Japan sees its number of islands double after recount

He also witnessed large rocks hurtling through the air and bands of brown pumice stones floating in the sea, which had changed colour as a result of the eruption, Kyodo reported.

Iwoto – the scene of one of the bloodiest battles of the Pacific war and one of 111 active volcanoes in Japan – is located near another new island that was formed after an eruption in 2021. Iwoto island was previously known as Iwo Jima but was renamed by Japanese authorities in 2007.

The area is accustomed to dramatic bursts of volcanic activity. Japan’s meteorological agency said similar eruptions had been observed near Iwoto between July and December last year and in June this year.

Maeno said the recent island formation was proof that magmatic activity had returned to the area. The new island could grow larger and change shape if the eruptions continue, but it could also disappear beneath the waves. Islands formed in a similar way in the area in 1904, 1914 and 1986 all disappeared due to erosion.

New islands made up of ash and rock fragments could struggle to resist constant battering by waves, but continued volcanic activity could produce lava flows that eventually form a harder, more durable surface.

In 2013, weeks of volcanic activity formed an island that merged with an existing island to create a new landmass that for a while bore a resemblance to the cartoon dog Snoopy.

Earlier this year, geographers said the Japanese archipelago, previously thought to comprise four main islands and about 6,000 much smaller and mostly uninhabited ones, was actually made up of twice as many. Using digital mapping technology, the Geospatial Information Authority of Japan said it had identified a total of 14,125 islands – 7,273 more than previously thought.

While it gains new islands, Japan occasionally loses them. Esanbe Hanakita Kojima, which was located 500 metres off the coast of Hokkaido, is thought to have slipped beneath the waves unnoticed in 2018.

No one realised it had disappeared until the author Hiroshi Shimizu visited the area to write a sequel to his picture book on Japan’s “hidden” islands.