50 million-year-old volcano cluster discovered off Sydney

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 that while searching for the nursery grounds for larval lobsters the ship was also routinely mapping the seafloor when the volcanoes were discovered in 4,900 metres of water.

“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.

The location of the sunken caldera. Image: Bright Earth e-Atlas Basemap

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.”

“On board the new MNF vessel, 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.

Professor Suthers said the 94-metre Investigator has other capabilities that marine scientists in Australia have never had before, and the vessel will be key to unlocking the secrets of the oceans around our continent and beyond.

One of the larval lobster specimens collected during the expedition. Photo: Marine National Facility

“Investigator is able to send and receive data while we’re at sea, which meant the team back on base at UNSW in Sydney could analyse the information we were collecting at sea and send back their analysis, along with satellite imagery, so we could chase the eddies as they formed,” Professor Suthers said.

“This is the first time we’ve been able to respond directly to the changing dynamics of the ocean and, for a biological oceanographer like me, it doesn’t get more thrilling,” Professor Suthers said.

“It was astounding to find juvenile commercial fish species like bream and tailor 150 kilometres offshore, as we had thought that once they were swept out to sea that was end of them. But in fact these eddies are nursery grounds along the east coast of Australia.”

Oceanographers from UNSW release satellite drifters from the RV Investigator. Photo: Marine National Facility

The research voyage led by Professor Iain Suthers departed Brisbane on 3 June and concluded on 18 June in Sydney, with 28 scientists from UNSW, La Trobe University, the University of British Columbia, the University of Sydney, the University of Auckland, the University of Technology Sydney, and Southern Cross University.

The centre of the volcanic cluster is 33 31 S, 153 52 E, which is 248 kilometres from Sydney Heads. The cluster is 20 kilometres long and six kilometres wide and the seafloor is 4890 metres deep, with the highest point in the cluster rising up to 3,998 metres.

See a photo gallery of the fish and lobster specimens collected by the expedition here.