Why Australia's east coast is a hotbed of volcanic activity

A team of geoscientists at the University of Sydney has discovered why Australia’s east coast is such a hotbed of volcanic activity. The findings may help to explain patterns of volcanic activity in other regions as well. 

The remnants of hundreds of volcanoes can be found across the east coast of Australia, and scientists have struggled to explain why so many eruptions have occurred over the past 80 million years.

“We aren’t on the famous Pacific ‘Ring of Fire’ that produces so many volcanoes and earthquakes,” said study co-author Dr. Ben Mather. “So, we needed another explanation why there have been so many volcanoes on Australia’s east coast.”

Dr. Mather explained that many of the volcanoes that form in Australia are one-off events. “Rather than huge explosions like Krakatoa or Vesuvius, or iconic volcanoes like Mount Fuji, the effect is more like the bubbles emerging as you heat your pancake mix.”

The remnants may look like regular hills or like notable structures such as Cradle Mountain in Tasmania or the Organ Pipes in Victoria. Many of the remnants are yet to be identified, said Dr. Mather.

“Under our east coast we find a special volatile mix of molten rock that bubbles up to the surface through the younger, thinner east coast Australian crust.”

The researchers analyzed how hundreds of eruptions occurred along the east coast, focusing mostly on “recent” peaks of volcanic activity in the last two to 20 million years. 

“Most of these eruptions are not caused by Australia’s tectonic plate moving over hot plumes in the mantle under the Earth’s crust. Instead, there is a fairly consistent pattern of activity, with a few notable peaks,” explained study co-author Dr. Maria Seton.

The team noticed that these peaks coincided with increased volume of seafloor material being pushed under the continent from the east by the Pacific plate.

“The peaks of volcanic activity correlate nicely with the amount of seafloor being recycled at the Tonga-Kermadec trench east of New Zealand,” said Dr. Mather. 

Based on their findings, the team has constructed a new model that unifies the observations of eruptions occurring over millions of years along Australia’s east coast. “The most recent event was at Mount Gambier in Victoria just a few thousand years ago,” noted Dr. Mather.

In a process known as subduction, the seafloor of the Pacific plate is being pushed under the Australian plate. The material is literally shoved under the Australian continental shelf.

“From there it is being slammed into the transition zone between the crust and the magma at depths of about 400 to 500 kilometers. This material is then re-emerging as a series of volcanic eruptions along Australia’s east coast, which is thinner and younger than the center and west of the continent,” said Dr. Mather.

He explained that this subduction process is not unique to the Australian east coast, but what sets the east Australia-Zealandia region apart is that the seafloor being pushed under the continent from the western Pacific is highly concentrated with hydrous materials and carbon-rich rocks. “This creates a transition zone right under the east coast of Australia that is enriched with volatile materials.”

The model may also be applied to other intraplate volcanic regions in the Western United States, Eastern China, and near Bermuda, according to the researchers.

“We now need to apply this research to other corners of the Earth to help us understand how other examples of enigmatic volcanism have occurred,” concluded study co-author Professor Dietmar Müller.

The study is published in the journal Science Advances.

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By Chrissy Sexton, Earth.com Staff Writer