The volcano, Rumble III, is about 200 miles offshore and part of the South Kermadec Ridge. The volcanic cone rises more than 7,000 feet from the sea floor.
Cornel de Ronde, one of the chief scientists on a research ship operated by GNS, a scientific agency owned by the New Zealand government, said that the volcano has changed shape since it was mapped in 2007, The Dominion Post reported. The top of the summit cone is now almost 1,000 feet below the surface, and the 2500-foot-wide crater has almost filled in.
"This suggests there has been a major eruption that collapsed the summit cone and filled the adjacent crater," de Ronde said.