Australasian Science: Australia's authority on science since 1938

Australia’s Record-Breaking Volcano Chain

The world’s longest known chain of continental volcanoes has been uncovered, running 2000 km across Australia from the Whitsunday Islands in north Queensland to central Victoria. The volcanic chain was created over the past 33 million years as Australia moved northwards over a hotspot in the Earth’s mantle.

“We realised that the same hotspot had caused volcanoes in the Whitsundays and the central Victoria region, and also some rare features in New South Wales roughly halfway between them,” said Dr Rhodri Davies of The Australian National University. “The track is nearly three times the length of the famous Yellowstone hotspot track on the North American continent.”

This kind of volcanic activity is surprising because it occurs away from tectonic plate boundaries, where most volcanoes are found. The hotspots are thought to form above mantle plumes, narrow upwellings of hot rock that originate at the boundary between the Earth’s core and mantle almost 3000 km below the surface.

The study, published in Nature, found that sections of the track have no volcanic activity because the Australian continent is too thick to allow the hot rock in the mantle plumes to rise close enough to the Earth’s surface for it to melt and form magma. The plume only created volcanic activity where the Earth’s solid outer lithosphere was thinner than 130 km.

The findings will help scientists to reconstruct the past movements of continents from other hotspots.

Co-author Prof Ian Campbell said the telltale sign that the continent is just thin enough for melting to begin is the formation of an unusual mineral called leucitite, which is found in low-volume magmas that are rich in elements such as potassium, uranium and thorium. “Now that we know there is a direct relationship between the volume and chemical composition of magma and the thickness of the continent, we can go back and interpret the geological record better,” he said.

Davies said the mantle plume that formed the Australian volcanoes is probably still in existence under the sea a little to the northwest of Tasmania. “There are observations of higher mantle temperatures and increased seismicity in this region,” he said.

The scientists have named the volcanic chain the Cosgrove hotspot track.