Submerged Volcanoes Discovered off Sydney (IMAGE) University of New South Wales Caption 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 largest is 1.5 kilometres across the rim and rises 700 metres from the sea floor. Credit Marine National Facility Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.