|The brighter and more concentrically zoned crystals with nice straight edges are the volcanic zircons. |
Well travelled: these zircon crystals took a 2300-kilometre trip
Giant ancient supervolcanoes threw rock right across Australia
A blast from the past? The east coast of Australia was once lined by volcanoes that were so explosive they could shoot sand-sized particles 2300 kilometres – all the way across to the west coast.
The volcanic activity occurred 100 million years ago, at a time when New Zealand began tearing away from Australia’s eastern edge.
Until recently, the only evidence of the scale of these eruptions were the 20-kilometre-wide dormant craters and the solidified lava flows left behind.
But now, Milo Barham at Curtin University in Western Australia and his colleagues have found that these eastern Australian volcanoes flung material to the other side of the country.
The researchers were drilling beneath the Nullarbor plain in remote Western Australia when they discovered sand-sized zircon crystals that did not match any of the region’s typical rock compositions.
Instead, the crystals matched volcanic rock in the Whitsundays area on the country’s north-east coast in both age and geochemical make-up.
“We didn’t find anything else from the east coast – just these very distinctive grains,” says Barham. “Initially, we thought there might be some volcanism in Western Australia, but we couldn’t find any evidence.”
Two clues ruled out the possibility that river systems had carried the zircon crystals across the country: they were so well preserved and fossils in the rocks indicated that the crystals were of an identical age.
The finding points to the sheer force of the east coast volcanoes, says Barham. The eruptions would have been tens to hundreds of times more powerful than any documented in human history. An equivalent eruption today would be heard in the west coast city of Perth.
Tremendous volcanic activity was happening all around the world 100 millions of years ago due to the disintegration of the supercontinent Gondwana, says Scott Bryan at Queensland University of Technology in Brisbane.
Modern volcanoes can spew fine particles of ash that are carried by winds over large distances, as happened in 2010 when Iceland’s Eyjafjallajökull volcano released an ash plume that grounded flights across Europe.
But they lack the power to hurl larger particles thousands of kilometres.
The biggest known super-eruption occurred from Toba volcano in Indonesia 75,000 years ago. This propelled sand-sized particles over a 2700-kilometre radius.
Barham’s work hints that Australia’s east coast volcanoes may have been in a similar league, says Bryan. “It reinforces the potential scale of these eruptions.”