Australia’s east coast is littered with the remnants of hundreds of volcanoes — the most recent just a few thousand years old — and scientists have been at a loss to explain why so many eruptions have occurred over the past 80 million years.
Now, geoscientists at the University of Sydney have discovered why part of a stable continent like Australia is such a hotbed of volcanic activity. And the findings suggest there could be more volcanic activity in the future.
“We aren’t on the famous Pacific ‘Ring of Fire’ that produces so many volcanoes and earthquakes,” said Dr. Ben Mather from the School of Geosciences and the EarthByte group at the University of Sydney.
“So, we needed another explanation why there have been so many volcanoes on Australia’s east coast.”
Many of the volcanoes that form in Australia are one-off events, he said.
“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,” Dr. Mather said.
Their remnants can look like regular hills or notable structures like Cradle Mountain in Tasmania, the Organ Pipes in Victoria, the Undara Lava Tubes in Queensland and Sawn Rocks, near Narrabri, in NSW. Many are yet to be identified, Dr. Mather said.
So, what is happening?
“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,” he said.
The study is published today (December 16, 2020) in the journal Science Advances.
Dr. Mather and his team looked at how hundreds of eruptions have occurred along the east coast from North Queensland to Tasmania and across the Tasman to the largely submerged continent Zealandia. They were particularly interested in ‘recent’ peaks of volcanic activity 20 million and 2 million years ago.
“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,” said co-author Dr. Maria Seton, from the School of Geosciences and EarthByte group.
Animation of tectonic plate movement and incidence of volcanoes over the past 120 million years. Blue shading shows subducted material from the Pacific plate under the Australian plate. Credit: The University of Sydney
What tipped them off was that these peaks were happening at the same time there was increased volume of sea-floor 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,” Dr. Mather said.
Taking this evidence Dr. Mather and his team have built a new model that unifies the observations of so many 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,” he said.
While the model explains the consistent volcanic activity, it can’t predict when the next volcano will emerge.
How it happens
The sea floor of the Pacific plate to the east is being pushed under the Australian plate. This process is called subduction. The material is literally being pushed under the Australian continental shelf, starting at the Tonga-Kermadec Trench east and north of New Zealand.
“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,” Dr. Mather said.
This subduction process is not unique to the Australian east coast.
“What sets the east Australia-Zealandia region apart is that the sea-floor 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 new explanation improves on previous models that have suggested volcanoes in Victoria were due to convection eddies in the mantle from being near the trailing edge of the tectonic plate or models that relied on the plate passing over hot spots in the mantle.
“Neither of these gave us the full picture,” Dr. Mather said. “But our new approach can explain the volcanic pattern up and down the Australian east coast.”
Dr. Mather said this model could also explain other intraplate volcanic regions in the Western USA, Eastern China and around Bermuda.
Co-author Professor Dietmar Müller, Joint Coordinator of the EarthByte group in the School of Geosciences, said: “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.”
Reference: “Intraplate volcanism triggered by bursts in slab flux” by Ben R. Mather, R. Dietmar Müller, Maria Seton, Saskia Ruttor, Oliver Nebel and Nick Mortimer, 16 December 2020, Science Advances.
The research, led by geoscientists at the University of Sydney was undertaken with researchers from Monash University and GNS Science in Dunedin, New Zealand.
I understood that the so-called “volcanics” at Cradle Mountain in Tasmania consist of a thick sill of intrusive dolerite formed during the trans-Gondwana 170-180 Ma thermal event that produced the dolerite intrusions now capping many mountains in Tasmania and which correlate with the extremely widespread and well-known Jurassic Ferrar Dolerite of Antarctica and the Kirwan dolerite in the Reefton area of NZ.
It is of interest that some of eastern Australia’s Tertiary volcanic rocks are known as the sources for the alluvial rubies found in Queensland, NSW, Victoria and Tasmania and also rare industrial-quality diamonds reported from NSW.
“The material is literally being pushed under the Australian continental shelf …”
Ever try to push a thread through the eye of a needle, or a wet spaghetti noodle through a hole the same diameter? It is more likely the plate is being pulled by the mantle convection cell under the crustal material, or being pulled down by its greater density than the over-riding crust.
Very Interesting Research.
Some thoughts and ideas for considerationand possible implementation going forward as more and more data becomes available
1. Extend the thinking using Pastdiction based on past data to an Interplate Theory of PLate Tectonics, Subduction and movement of tectonic plates , the momentum related to the same which creating enormous momentum and forces and come up with a Unified Theory of Earthquake predictions based of Predictive Analytics
2. Just because we have only been able to dig to a depth of of 7 to 8 Kilometers into the earths crust to try and understand the processes happening deep within the bowels of the Planet Earth, does not mean that we cannot gain knowledge aabout the possible causes which could result in future earthquakes “Visibility” of the processes can also be modelled using the data gathered for various temperatures and pressures and viscosity of semi liquids underneath the Earths crust at the Lithosphere and Asthenosphere level — at least on a Theoritical basis. The molten Lava in the Volcanoes and their eruptions, as forces build up over various time frames can also be data based and based on past information and sattelite information on he effect of these forces building up on the Earhs Crust And can be monitored and captured at the micro and mini micro levels using ultra sensiive sensors to monitor seismic activity, which acn be made to survive and penetarte deeper tahn attempts to physically attempt human access, which could possibly reveal patterns on the impact of the build up forces resulting in different types of stress , due to these forces , monitoring which can be used to accurately predict Earthquakes , Volcanic Activity and other “Low Risk – High Catostrophic- Black Swan Events” which has hige impact on all life and property and probably can be done reasonably accurately , as is the case with short-term wheather forecasting and we could probablydo so as accurately as the whether forecast AND is very much a possible and doable task in my personal opinion, withe computing and scientific capability and knowledgewe have gained/
3. After all the only change is that we need to understand the forces of Nature on the Lithosphere, asthenosphere , …. as well , as we are able to do so in the short term for the wheather forecast in the atmosphere and forecast it reasonably accruarately! The ability to do so for the medium term and and longer term is suspect currently, and we need to do this with greater data and better understanding of the reltive nature of time at the Gross level to improve accuracy of such medium and long term forecast.
4. Once mastered at the atmospheric level , the understanding can be extended to the lithosphere, asthenosphere …. all based on geodynamics of plate tectonics subduction, volcanic activity and other forces at the planetary level and its impact on evolution of life , over the life-time of the earth ( estimated at 4 billion years) and the life of the Universe ( estimated at 14 billion years). All based on Data.
5. 5 million years, , 80 million years to 100 million years are very very short terms compared to these estimates. Analysis of the geochemical outputs of of volcanic eruption products , may be basically scaratching the surface , but is a good starting point. Theory needs to precede experimaents.
6. Edge driven convection is just one force. Are there others driving volcanic activity” Also, 5000 Km stretch of Australian Coast…..? Maybe different stokes for different folks applies as the lithosphere and asthenosphere may differ over the different planetary stretches as :
(a) The earths crust may be different (thinner, Thicker) , as can also the temperatures and Pressures prevailing in the Asthenosphere and Lithosphere ….. and driving the catostrophic events. So lumping it together may mislead.
(b) Physics of Planetary Forces and their interaction with Gravitation Forces at equilibrium with the Sun, other Planets in the solar system, and the stars in the galaxy, the galaxy’s in the milky way, the unkown forces like undiscovered planets and other planetary bodies, dark matter, countless stars in the Universe and Multiverse needs to be understood and has to determined using data , without making the assumptions we constantly make which could be misleading. We have always assumed hat these are negligible. Not so sure.
(7) Chemical Signatures for msntle domain needs to be coupled with te temperatures , pressures, of the meting points of elements, the molecules constituting these environments and also quantum chemistry and quantum physics at the sun-atomic level and Mass & energy interactions at the Gross level where these are occurring. This is because these could approach the forces happenning in the sun and fusion deep within the Core ofthe rocky planet where molten lava (liquid) and Gaseous matter may be building up forces needs to be better understood.
(8) Jupiter which is a gaseous planet may give some clues on these at the gaseous level. Get accurate data at Solar system level and analyse in light of (6) above. Then Syntheise a Theory of Volvcanic activity and Theory of Earthquakes at Planetary level and forecast accuarately.
All views expressed are persoal and not binding on anyone. Best of luck.