Four undersea volcanoes have been discovered off Sydney. Credit:CSIRO One of the scientists on the voyage, oceanographer Moninya Roughan, said their discovery came as a complete surprise and was serendipitous because the ship was routinely mapping the sea floor. "It was the last night of the voyage and we'd set a path from Forster to Sydney and we just happened to go over these volcanoes," Dr Roughan, from the University of NSW, said. "We had the swathe mappers going constantly throughout the cruise and two support staff who were constantly watching the output and reporting on any features," she said. "One of the guys came up and said, 'Look at these new volcanoes that have never been discovered before.' "

The volcanoes sit in about 4900 metres of water. Credit:UNSW The extinct volcanoes are now calderas, which form after a volcano erupts and the land around it collapses, forming a crater. Volcano expert Richard Arculus, from the Australian National University, said they were at least 50 million years old and formed near the boundary of an ancient ridge separating two ocean plates. Marine biologists were searching for larval lobsters when they found the volcanoes. Credit:CSIRO They had never been discovered before because the sonar on Australia's previous research vessel, Southern Surveyor, could map the sea floor only to 3000 metres, which left half of Australia's ocean territory out of reach.

"On board the Investigator we have sonar that can map the sea floor to any depth, so all of Australia's vast ocean territory is now within reach, and that is enormously exciting," Professor Arculus said. The voyage, led by University of NSW marine biologist Iain Suthers, was one of the first for the Investigator, which is managed by the CSIRO and has capabilities that marine scientists in Australia have never had before. "It's a kick-arse ship. We should be so proud of it," he said. While the federal government has funded the ship to run 180 days a year, scientists are hopeful it will be funded to run all year long. "With these sorts of discoveries, they'll see it's crazy to have it tied up to the wharf," Professor Suthers said.

"If we just found these volcanoes by chance chasing larval lobster, imagine what we could find with a dedicated survey," he said. "It's ironic that we're about to get the first close-up pictures of Pluto but we had no idea about these beautiful volcanoes just off the coast of Sydney." The first Investigator voyage was designed to find small ocean eddies, about 20 to 50 kilometres in diameter, that form in the shallow region of the east coast of Australia. These eddies are full of nutrients and larval fish species, Dr Roughan said. "But the thing is they're really hard to find so this was the first dedicated research group to look for these features," she said.

"On the last night we were looking at these warm core eddies that sit off the coast of Sydney, which are much easier to find, and looking for lobster larvae when we stumbled across these volcanoes. "It was sheer luck that we went over them."