Japan has gained a new island as an undersea volcanic eruption occurred 1,200 kilometres south of Tokyo. The eruption began in October near Iwoto island, part of the Ogasawara island chain in the western Pacific. It has created a new landmass approximately 100 metres in diameter.

Fukashi Maeno, an associate professor at Tokyo University’s earthquake research institute, confirmed the formation of the new landmass.

The eruptions are classified as phreatomagmatic. They are a result of magma interacting with water, leading to plumes of smoke and ash that reach over 50 meters in height. During the volcanic activity, Maeno witnessed large rocks flying through the air and noticed bands of brown pumice stones floating in the sea. The sea had also changed colour due to the eruption.

Iwoto is the site of a pivotal World War II battle. It is one of 111 active volcanoes in Japan. The area has witnessed frequent volcanic activity, with eruptions occurring the previous year and in June this year.

The new island could continue to grow larger and change shape if eruptions persist. Or it could eventually erode and vanish beneath the waves, much like similar islands formed in 1904, 1914, and 1986.

Islands created from ash and rock fragments are susceptible to erosion by waves. However, continued volcanic activity may lead to the formation of more durable surfaces, possibly from lava flows. In a past example, a series of volcanic events in 2013 resulted in forming an island that eventually merged with an existing one, creating a new landmass that bore a striking resemblance to the cartoon character Snoopy for a time.

This event follows the revelation earlier this year that the Japanese archipelago once thought to consist of four main islands and around 6,000 smaller, mostly uninhabited ones, is composed of 14,125 islands, 7,273 more than previously believed. This finding was made possible through the use of digital mapping technology by the Geospatial Information Authority of Japan.

Japan gains new islands through volcanic activity, but the country also loses them occasionally. For instance, in 2018, Esanbe Hanakita Kojima, an island located 500 metres off the coast of Hokkaido, is believed to have vanished beneath the waves. Its disappearance went unnoticed until author Hiroshi Shimizu visited the area to work on a sequel to his picture book about Japan’s “hidden” islands.