WELLINGTON, New Zealand -- A volcanic eruption in Tonga has created a new island -- although one scientist said Wednesday it could soon disappear.

The volcano has been erupting for a month in the ocean about 65 kilometres northwest of the capital, Nuku'alofa. Last week it disrupted international air travel to the Pacific archipelago for several days.

New Zealand volcanologist Nico Fournier said he travelled by boat to within about a mile of the new island on Saturday to take a closer look.

He said it's made mainly of loose scoria and its dimensions are about 1.8 kilometres by 1.5 kilometres, and that it rises about 100 metres above the sea.

"It's quite an exciting site, you get to see the birth of an island," he said. "Visually it was quite spectacular, but there was no big sound coming with it, no boom. It was a bit eerie."

He said that once the volcano stops erupting, it will likely take the ocean no more than a few months to erode the island entirely. He said it would need to be made of lava or something more durable to survive.

Fournier, who works for New Zealand agency GNS Science, said he was able to establish that the volcano was mainly belching steam into the atmosphere, and that the small amount of ash it was sending out was rising no more than about 2 kilometres.

That will come as a relief to airlines, as it is the ash that can be dangerous to planes.

Fournier said the ocean around the island is likely fairly shallow, perhaps only about 100-200 metres deep. He said there is no name yet for the new island, and he has been told that any naming rights will fall to Tonga's king.