Researchers have discovered four extinct underwater volcanoes thousands of feet below the water off the coast of Sydney

The calderas are believed to have formed 50 million years ago when supercontinent Gondwana was splitting up into the regions we now know as Australia and New Zealand.

And this quartet of 'hotheads' may offer geologists clues about how exactly this tectonic movement took place.

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Buried thousands of feet below the water off the coast of Sydney researchers have discovered four extinct underwater volcanoes. The calderas (pictured) are believed to have formed 50 million years ago when supercontinent Gondwana was splitting up into the regions we now know as Australia and New Zealand

The volcanoes were discovered 125 miles (200km) off the southwestern Australian coast using the Investigator ocean explorer from the Commonwealth Scientific and Industrial Research Organisation (CSIRO).

Scientists from the University of New South Wales Australia were searching for nursery grounds for larval lobsters when the sonar images spotted the volcanoes 16,100 feet (4,900 metres) underwater.

The four extinct volcanoes in the cluster are calderas, which form after a volcano erupts and the land around them collapses, forming a crater.

HOW AUSTRALIA AND NEW ZEALAND PARTED WAYS Around 500 million years ago, the land on Earth was part of supercontinent Pangaea. Heat from under the crust causes the land to move and Pangaea broke into Laurasia and Gondwana. Laurasia formed the northern continents while Gondwana broke up into the southern, including Africa and Australia. New Zealand was formed by the Australian and Pacific plates sliding together. Some 170 million years ago Africa detached, followed by India and Madagascar 130 million years ago. The remaining eastern part of Gondwana, which contained the future Australia, New Zealand and Antarctica. Australis began to fracture around 80 million years ago, when New Zealand split from Australia and Antarctica and the Tasman Sea opened up. The land continued to separate into roughly the regions we have today for the next 20 million years. Advertisement

The largest is a mile (1.5km) across the rim and rises 230ft (700 metres) from the sea floor.

The centre of the cluster is at 33,31 S, 153,52 E - around 154 miles (248km) from Sydney Heads - and the cluster is 12 miles (20km) long and 4 miles (6km) wide.

And the highest point in the cluster rises up to 13,100ft (3,998 metres).

'The voyage was enormously successful,' said chief scientist Professor Iain Suthers.

'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.'

Investigator is fitted with sonar equipment that emits acoustic signals to the ocean floor, while receivers on the vessel record and interpret the 'echoes' that are sent back.

Marine National Facility's (MNF) previous research vessel, Southern Surveyor, could only map to 9,840 ft (3,000 metres), missing important geological features like the calderas, but the Investigator can map the ocean to any depth.

'The ship is constantly mapping the sea floor as it travels, opening up a previously undiscovered and unknown world,' explained CSIRO.

Professor Richard Arculus from the Australian National University said these particular types of volcanoes are really important to geoscientists because they are like windows into the seafloor.

The largest volcano in the cluster (pictured) is a mile (1.5km) across the rim and rises 230 ft (700 metres) from the sea floor. The total cluster sits at 16,100 feet (4,900 metres) of water deep, is 12 miles (20km) long and 4 miles (6km) wide and its highest point rises up to 13,100ft (3,998 metres)

The volcanoes were discovered 125 miles (200km) off the southwestern Australian coast (marked) using the Investigator ocean explorer from the Commonwealth Scientific and Industrial Research Organisation (CSIRO)

'They tell us part of the story of how New Zealand and Australia separated around 40 to 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,' he explained.

'On board 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.

He continued that sonar images of the in-line volcanoes show large craters in the top of each, which proves they have all erupted, possibly in an explosive manner.

Marine National Facility's (MNF) previous research vessel, Southern Surveyor, could only map to 9,840 ft (3,000 metres), missing important geological features like the calderas but the Investigator can map the ocean to any depth. An example of how the vessel maps the floor is pictured

'But there's no real chance (they) are going to erupt again...these guys have been dead for a long time,' he said.

'And volcanic activity in the Tasman Sea is extinct.'

However, according to the the voyage's chief scientist, a number of other exciting discoveries were made below the surface.

Professor Suthers said they located a 'hotspot' for lobster larvae and other small underwater critters.

'We had thought fish only developed in coastal estuaries, and that once larvae were swept out to sea that was end of them,' Professor Suthers said.

'But in fact, these eddies are nursery grounds for commercial fisheries along the east coast of Australia.'

Researchers said they also located a 'hotspot' for lobster larvae and other small underwater critters. 'We had thought fish only developed in coastal estuaries, and that once larvae were swept out to sea that was end of them,' the chief scientist said.' This chauliodontidae was one of the larvae uncovered by the research team