TOKYO (AFP) - An erupting volcanic island that is expanding off Japan could trigger a tsunami if its freshly formed lava slopes collapse into the sea, scientists said on Tuesday.
The small, but growing, island appeared last year and quickly engulfed the already-existing island of Nishinoshima, around 1,000km south of Tokyo. It now covers 1.26 sq km.
The island's craters are currently spewing out 200,000 cu m of lava every day - enough to fill 80 Olympic swimming pools - which is accumulating in its east, scientists said. "If lava continues to mount on the eastern area, part of the island's slopes could collapse and cause a tsunami," warned Professor Fukashi Maeno, assistant professor of the Earthquake Research Institute at the University of Tokyo.
He said a rockfall of 12 million cu m of lava would generate a 1m-high tsunami that could travel faster than a bullet train, hitting the island of Chichijima - 130km away - in around 18 minutes, he said.
Chichijima, home to some 2,000 people, is the largest island in the Ogasawara archipelago, a wild and remote chain that is administratively part of Tokyo.
"The ideal way to monitor and avoid a natural disaster is to set up a new tsunami and earthquake detection system near the island, but it's impossible for anyone to land on the island in the current situation," Prof Maeno added.
An official from the Japan Meteorological Agency, which monitors earthquakes and tsunamis, said the agency is watching for any signs of anything untoward.
"We studied the simulation this morning, and we are thinking of consulting with earthquake prediction experts... about the probability of this actually happening, and what kind of measures we would be able to take," he said.
Japan's north-east was ravaged by a huge tsunami in March 2011, when a massive undersea earthquake sent a wall of water barrelling into the northeast coast, killing more than 18,000 people and wrecking whole towns.