I may be an astronomer, but I kind of love volcanoes. Our world is active and changing, and the volcanoes that dot its surface are often the consequence of how our world’s tectonic plates are moving under, over, and around one another.

Sometimes, however, we find volcanoes that have nothing to do with moving plates. Hawai’i — the Kīlauea volcano we started today with — is related to a hotspot that just likes to melt holes through the crust and form new islands. Sometimes, however, we see volcanoes and have no idea why.

For decades the east coast volcanoes of Australia have been a bit of a mystery. While New Zealand, which is a several-hour flight from Australia, is on the ring of fire, Australia is on its own plate and is technically a different continent. Australia is supposed to be geologically stable — not a lot of volcanoes, not a lot of earthquakes, just a lot of animals that will try and kill you.

But, surprisingly, the eastern coast of Australia has stretches of hundreds of dormant volcanoes that have been active as recently as 80 million years ago. They have a shape that indicates they were formed out of runny lava, more like Kīleaua than Mt. Etna, and mostly look like hills, with a few exceptions, like the Organ Pipes formation in Victoria.

In a new paper in Science Advances, a team led by Ben Mather looked at where random oozy lava could be originating. According to co-author Maria Seton: 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. 

Mather goes on to add: The peaks of volcanic activity correlate nicely with the amount of seafloor being recycled at the Tonga-Kermadec trench east of New Zealand.

The team built new computer models for the region’s tectonics and discovered that, as the Pacific slab crawls under the Zealandia plate, which New Zealand sits on, it displaces material rich in gases that begin to rise up through higher density material, breaking through at the surfaces, to form rolling gentle volcanoes. One really cool implication of this work is that it implies new volcanoes could still spring up in Australia, adding a bit of geologic activity to this otherwise staid landscape.

More Information

The University of Sydney press release 

“Intraplate volcanism triggered by bursts in slab flux,” Ben R. Mather et al., 2020 December 16, Science Advances