Japan earthquake and Tsunami 2011 - Shocking video

An erupting volcanic island that is expanding off Japan could trigger a tsunami if its freshly-formed lava slopes collapse into the sea, scientists say.

The small, but growing, island appeared last year and quickly engulfed the already-existing island of Nishinoshima, around 1000 kilometres south of Tokyo.

It now covers 1.26 square kilometres.

The island's craters are currently spewing out 200,000 cubic metres 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 Fukashi Maeno, assistant professor of the Earthquake Research Institute at the University of Tokyo.

He said a rockfall of 12 million cubic metres of lava would generate a one metre tsunami that could travel faster than a bullet train, hitting the island of Chichijima - 130kms away - in around 18 minutes, he said.

Chichijima, home to about 2000 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 is.