Australia's new ocean-going research vessel Investigator has discovered extinct volcanoes likely to be 50 million years old about 250 kilometres off the coast of Sydney. The chief scientist for the voyage, UNSW Australia marine biologist Professor Iain Suthers, said the volcanoes were discovered in 4,900 meters of water during a search for nursery grounds for larval lobsters. At the same time the ship was also routinely mapping the seafloor.

"The voyage was enormously successful. Not only did we discover a cluster of volcanoes on Sydney's doorstep, we were amazed to find that an eddy off Sydney was a hotspot for lobster larvae at a time of the year when we were not expecting them," Professor Suthers said.

The four extinct volcanoes in the cluster are calderas, which form after a volcano erupts and the land around them collapses, forming a crater. The largest is 1.5 kilometres across the rim and it rises 700 metres from the sea floor.

Professor Richard Arculus from the Australian National University, an igneous petrologist and a world-leading expert on volcanoes, said these particular types of volcanoes are really important to geoscientists because they are like windows into the seafloor.

"They tell us part of the story of how New Zealand and Australia separated around 40-80 million years ago and they'll now help scientists target future exploration of the sea floor to unlock the secrets of the Earth's crust," Professor Arculus said.

"They haven't been found before now because the sonar on the previous Marine National Facility (MNF) research vessel, Southern Surveyor, could only map the sea floor to 3,000 metres, which left half of Australia's ocean territory out of reach." "