The east coast of Australia was once lined by active volcanoes that were so explosive that they ejected debris up to a distance of 2,300 kilometers (1,430 miles) away, reaching as far as the western coast of the continent. These “super-eruptions” took place 106 million years ago, just as Australia was rifting away from Antarctica during the break-up of the supercontinent Gondwana.
According to a new study in the journal Geology, the team from Curtin University (CU) were actually looking for sediments in Western Australia (WA) in order to find out how the southern section of the continent evolved during its segregation from Antarctica. When they stumbled across what looked like volcanic debris, they couldn’t quite believe what they had found at first.
Within this debris were crystals known as zircons. These resilient mineral inclusions tend to form during volcanic activity, but they appear in so-called “arc volcanism” far more than any other variant, which involves a denser tectonic plate sliding or “subducting” beneath a less dense plate. This mechanism produces complex magma sources that are often quite viscous and gas-rich, which ultimately means any subsequent volcanism is particularly explosive.
By dating these crystals and looking for specific geochemical markers, the team matched these unique deposits to Early Cretaceous volcanic activity all the way on the other side of Australia. The distance these crystals travelled allowed the team to estimate the magnitude of the eruption that produced them, and there’s no doubt about it – it would have been hundreds of times more powerful than anything experienced in human history.
This eruption, or series of eruptions, would have darkened the sky with ash before blanketing much of the southern hemisphere. The paroxysm would have also unleashed masses of global warming-inducing carbon dioxide.
“If an event of this magnitude were to happen today it would have devastating effects on our society and likely would drive massive crop failures, famine and war,” the study’s lead author Dr Milo Barham, a sedimentologist from CU, said in a statement.
Image in text: The zircons found in WA that were ejected from a massive volcanic province 2,300 kilometers away. Credit: Milo Barham/CU