Researchers have discovered the world's lengthiest chain of continental volcanoes — formed over 33 million years and stretching 1,200 miles across Australia.
The chain of volcanoes was created by a hotspot in Earth's mantle below Australia as the continent moved northward over those millions of years.
The ancient string of volcanoes stretches from the northern Queensland coast down southwest through the center of New South Wales, before ending at the extinct Cosgrove volcano in Victoria.
"This track, which we've named the Cosgrove hotspot track, is nearly three times as long as the famous Yellowstone hotspot tracks on the North American continent," said study leader Rhodri Davies of the Australian National University.
Unlike most volcanoes, which are located at the boundaries of tectonic plates, those in the Australian chain were created by a hotspot — a narrow upwelling of hot rock from 1,800 miles beneath the surface at the core-mantle boundary.
As the tectonic plate on which Australia sits moved north-northeast over the hotspot, the chain of volcanoes formed — far from the plate's boundaries.
"Australia is actually the fastest moving continent on Earth, moving towards Indonesia at around seven centimeters per year," Davies said.
The study, which was published in the journal Nature, began with researchers looking at 15 extinct volcanoes in the continent's east, which had been known for some time and which appeared to line up in a general north-to-south track.
"We realized 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," Davies explained.
Gaps in the chain – areas with no volcanic activity – exist because the crust of the Australian continent is too thick in those regions for the upwelling hot rock to get close enough to Earth's surface where it can melt and form magma.
Only in the regions where the outer layer of the crust, called the lithosphere, was less than 80 miles thick could volcanic activity occur, according to the researchers.
Volcanoes in central Queensland forced their way through lithospheres around 50 miles thick, while in New South Wales and Victoria they erupted through lithospheres around 62 miles thick, the researchers note.
The mantle plume that created the volcanic chain likely still exists, Davies explained, and would be underneath the ocean just to the northwest of the island state of Tasmania, south of Australia.
"There is some seismicity in this region, there's been some earthquakes around that location recently which does hint that something is going on there, but we haven't been able to find any seamounts or volcanic regions at present," Davies said.