Australia’s east coast is teeming with the remains of hundreds of volcanoes – the latest in just a few thousand years – and scientists have been missing out on why so many eruptions have occurred over the last 80 million years. gone.
Now, geoscientists at the University of Sydney have discovered why part of a stable continent like Australia is so full of volcanic activity. And the findings show that there may be more volcanic activity in the future.
“We’re not on the famous ‘Ring of Fire’ in the Pacific Ocean that makes so many volcanoes and earthquakes,” said Dr Ben Mather from the University of Sydney’s School of Geosciences and EarthByte.
“So we needed another explanation for why there are so many volcanoes on Australia’s east coast.”
Many of the volcanoes that form in Australia are one-off events, he said.
“Instead of large eruptions like Krakatoa or Vesuvius, or iconic volcanoes like Mount Fuji, the effect is more like the bubbles appearing as you heat your pancake mix,” said Dr. Mather.
What remains of them may resemble regular hills or famous structures such as Cradle Mountain in Tasmania, the Organ Pipes in Victoria, the Undara Lava Tubes in Queensland and Sawn Rocks, near Narrabri, in NSW. Much remains to be celebrated, Dr Mather said.
So what’s happening?
“Beneath our east coast we are looking for a unique volatile mixture of molten rock that rises to the surface through the younger, thinner Australian crust,” he said.
The study is published today (December 16, 2020) in the journal Advances in science.
Dr Mather and his team looked at how hundreds of explosions have taken place on the east coast from North Queensland to Tasmania and across the Tasman to the underground continent of New Zealand. They were particularly interested in the peaks of volcanic activity in recent 20 million and 2 million years ago.
“Most of these explosions are not caused by an Australian tectonic plate moving over hot plugs in the mantle beneath the Earth’s crust. Instead, there is a fairly consistent pattern of activity, with a few peaks, ”said co-author Dr. Maria Seton, from the School of Geology and EarthByte group.
The animation of tectonic plate movement and the frequency of volcanoes over the last 120 million years. A blue shade indicates material extracted from the Pacific plate under the Australian plate. Credit: University of Sydney
What put them off was that these peaks were occurring at the same time that more seabed material was being pushed under the eastern continent by a Pacific plate.
“The peaks of volcanic activity link nicely to the amount of seabed recycling at the Tonga-Kermadec trench east of New Zealand,” said Dr Mather.
Taking this evidence, Dr Mather and his team have built a new model that responds to the many explosions that have taken place over millions of years on Australia’s east coast.
“Mount Gambier’s latest event in Victoria was just a few thousand years ago,” he said.
Although the model describes constant volcanic activity, it cannot predict when the next volcano will erupt.
As it happens
The seabed on the eastern Pacific plate is pushed under the Australian plate. This process is called referral. The material is literally being pushed under the shelf of the Australian continent, starting at the Tonga-Kermadec Trench east and north of New Zealand.
“From there, it is applied to the range of motion between the bark and the magma at a depth of about 400 to 500 kilometers. This material then reappears as a series of volcanic eruptions on the east coast of Australia, which are thinner and younger than the central and western continents, ”said Dr Mather.
The removal process is not unique to the east coast of Australia.
“What sets the eastern Australia-Zealand region apart is that the seabed that is pushed beneath the continent from the western Pacific Ocean is full of hydrous materials and carbon-rich rocks. This is creating a movement zone just below the east coast of Australia full of volatile materials. ”
The new definition builds on previous models that have proposed volcanoes in Victoria as a result of convection eddies in the mantle from being close to the sliding edge of the tectonic plate or dependent models. to the plate passing hot places in the mantle.
“Neither of them gave us the full picture,” said Dr Mather. “But our new approach can explain the volcanic pattern up and down the east coast of Australia.”
Dr. Mather said this model could also define other intraplate volcanic regions in the Western USA, East China and around Bermuda.
Co-author Professor Dietmar Müller, Co-ordinator of the EarthByte group in the School of Geosciences, said: “We now need to apply this research to other parts of the Earth to help us understand how other examples of enigmatic volcanism have occurred. ”
Information: 16 December 2020, Advances in science.
DOI: 10.1126 / sciadv.abd0953
The research, led by geologists at the University of Sydney, was carried out by researchers from Monash University and GNS Science in Dunedin, New Zealand.