Australia’s east coast is littered with the remains of hundreds of volcanoes – the most recent only a few thousand years old – and scientists have been unable to explain why so many eruptions occurred in the 1980s. last million years.
Today, geoscientists at the University of Sydney have discovered why part of a stable continent like Australia is a hotbed of volcanic activity. And the results suggest there may be more volcanic activity in the future.
“We are not on the famous Pacific ‘ring of fire’ that produces so many volcanoes and earthquakes,” said Dr Ben Mather of the School of Geosciences and the EarthByte group at the University of Sydney.
“So we needed another explanation why there were so many volcanoes on the east coast of Australia.”
Most of the volcanoes that form in Australia are one-time events, he said.
âRather than huge explosions like Krakatoa or Vesuvius, or iconic volcanoes like Mount Fuji, the effect is more like the bubbles that emerge when you heat your pancake mix,â Dr. Mather said.
Their remains may look like regular hills or remarkable structures like Cradle Mountain in Tasmania, organ pipes in Victoria, Undara lava tubes in Queensland, and Sawn Rocks near Narrabri, New South Wales. Many have yet to be identified, Dr Mather said.
So what is going on?
âUnder our east coast we find a special volatile mixture of molten rock bubbling on the surface through the younger and thinner Australian crust of the east coast,â he said.
The study is published today in the journal Scientists progress.
Dr Mather and his team examined how hundreds of eruptions occurred along the east coast from northern Queensland to Tasmania and across Tasman to the largely submerged mainland of Zealandia. They were particularly interested in the “recent” peaks of volcanic activity 20 million and 2 million years ago.
âMost of these eruptions are not caused by the movement of the Australian tectonic plate over hot plumes in the mantle beneath the earth’s crust. Instead, there is a fairly consistent pattern of activity, with a few peaks. notables, âsaid co-author Dr Maria Seton of the School of Geosciences and the EarthByte Group.
What warned them was that these peaks were occurring at the same time as there was an increased volume of seabed material pushed under the continent from the east by the Pacific plate.
“The peaks of volcanic activity correlate well with the amount of seabed recycled in the Tonga-Kermadec trench in eastern New Zealand,” said Dr Mather.
Taking this evidence, Dr Mather and his team built a new model that unifies the observations of so many eruptions that have occurred over millions of years along Australia’s east coast.
âThe most recent event took place at Mount Gambier in Victoria just a few thousand years ago,â he said.
Although the model explains the constant volcanic activity, it cannot predict when the next volcano will emerge.
How’s it going
The seabed of the Pacific Plate to the east is pushed under the Australian Plate. This process is called subduction. The material is literally pushed under the Australian continental shelf, from the Tonga-Kermadec trench in eastern and northern New Zealand.
“From there it is thrown into the crustal-magma transition zone at depths of about 400 to 500 kilometers. This material then reappears as a series of volcanic eruptions along the east coast. from Australia, which is thinner and younger than the center and west of the continent, âsaid Dr Mather.
This subduction process is not unique to the Australian east coast.
âWhat distinguishes the region of eastern Australia and Zeeland is that the seabed pushed under the continent from the western Pacific is highly concentrated in hydrous materials and carbon-rich rocks. This creates a transition zone just under the east coast of Australia which is enriched with volatiles. “
The new explanation improves upon previous models which suggested that the Victoria volcanoes were due to mantle convection vortices near the trailing edge of the tectonic plate or to models that relied on the passage of the plate to the above the hot spots of the coat.
âNone of these gave us the full picture,â Dr Mather said. “But our new approach may explain the top-to-bottom volcanic pattern of Australia’s east coast.”
Dr Mather said this model could also explain other intraplate volcanic regions in the western United States, eastern China and around Bermuda.
Co-author Prof Dietmar MÃ¼ller, co-coordinator of the EarthByte group at the School of Geosciences, said: âWe now need to apply this research to other corners of the Earth to help us understand how others examples of enigmatic volcanism have occurred.