The Commonwealth Science and Industrial Research Organisation's (Csiro) Research Vessel Franklin, based in Australia, found the Kavachi seamount had entered a new phase of eruptive activity after nine years of apparent dormancy.
The dramatic birth of a new volcanic island in the Pacific has been witnessed by an international team of scientists.
The rare event was captured on film by researchers during an expedition to the Solomon Islands.
The Commonwealth Science and Industrial Research Organisation's (Csiro) Research Vessel Franklin, based in Australia, found the Kavachi seamount had entered a new phase of eruptive activity after nine years of apparent dormancy.
Molten ash shot 500 metres (1,600 ft) into the air every five minutes of the team's 20-hour visit.
The peak of the volcano was forming a sandy, ashen beach two metres below sea level, with its regular, violent, bomb-like eruptions.
"We arrived at the seamount site to find waves breaking on the volcanic peak. Violent eruptions were taking place every five minutes," said expedition Chief Scientist Brent McInnes.
Unprecedented opportunity
Kavachi is 35 km (21 miles) from the closest island, in the western Solomons, and was first surveyed in the 1950s.
Dr McInnes said: "It was magma being ejected from the top of a magma chamber, which is below sea level. This magma has a lot of gas in it so it's a very explosive mixture whenever it comes close to the surface.
Neil Cheshire, Master of the RV Franklin, said: "We were able to approach to within 750 m (2,500 ft) of the erupting centre. We found that the volcano had grown dramatically since it was last surveyed in 1984."
Professor Richard Arculus, of the Australian National University Department of Geology, added: "Using Franklin to systematically sample freshly formed volcanic rocks from the flanks of an erupting submarine volcano is an unprecedented opportunity in the field of geology."
And researcher Gary Massoth said: "We detected numerous chemical and particle plumes in the water that extend at least 5 km (3 miles) from the centre of the volcano. This has been a great opportunity for us to obtain fundamental data on dynamic volcanic inputs to the ocean environment"