An underwater volcano erupted off Japan’s coast three weeks ago, giving birth to a new island.

The unnamed undersea volcano, located about 1,200 kilometers (750 miles) south of mainland Japan and a kilometer from Iwo Jima (half a mile) off the southern coast of Iwo Jima, began erupting on October 21.

Yuji Usui, an analyst in the Japan Meteorological Agency’s volcanic division, said that in early November, the island measured roughly 100 metres (328 feet) in diameter and was as high as 20 metres (66 feet) above the sea.

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This aerial photo shows steam billowing from the waters off Iwoto Island, Ogasawara town in the Pacific Ocean, southern Tokyo, on Oct. 30, 2023. A new island, 100 meters in diameter, formed by erupted rock, is seen near the steam, according to Kyodo News. (Kyodo News via AP)

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He added that the new island had already begun to erode due to its “crumbly” formation.

“We just have to see the development,” he said. “But the island may not last very long.”

He said experts are still analyzing the development, including details of the deposits. 

The new island could survive longer if it is made of lava or something more durable than volcanic rocks such as pumice.

In this photo provided by the Japan Maritime Self-Defense Force, steam billows from the waters off Ioto island, Ogasawara town in the Pacific Ocean, southern Tokyo, on Nov. 1, 2023.  (Japan Maritime Self-Defense Force via AP)

Photos of the eruption show large plumes of smoke above the tiny island, which is now part of the Ogasawara Island chain.

Of about 1,500 active volcanoes in the world, 111 are in Japan, which sits on the so-called Pacific “Ring of Fire,” according to the Japan Meteorological Agency.

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The Associated Press contributed to this report.