Australia was once home to hundreds of ancient volcanoes. We may finally know why

Geologically speaking, Australia is a very quiet place to live. Earthquakes are rare and usually mild, and like volcanoes, there has been less magma on the mainland in thousands of years.

It wasn’t always like this. In fact, the earth is full of the remnants of mysterious explosions that have destroyed the crust with astonishing regularity over the past 80 million years.

A new study shows that some of the most unusual periods of activity were due to the old seabed squeezing under the plate, providing the perfect stick for a wide course of blasting down the length of the ocean. -country.

From the steep cliffs of Cradle Mountain in Tasmania to Victoria’s famous Organ Pipes, to the impressive peaks of the Greenhouse Mountains of Queensland, an elegant series of monoliths follow the east coast of Australia like a crooked marrow.

It is unclear what caused them.

“We’re not on the famous‘ Ring of Fire ’in the Pacific Ocean that makes so many volcanoes and earthquakes,” says geoscientist Ben Mather from the University of Sydney.

“So we needed another explanation for why there have been so many volcanoes on Australia’s east coast.”

In many parts of the world, far from the edges of any tectonic plate, volcanoes are the result of rising heat erupting the crust. As the crust slips over patches of high temperatures, magma weaknesses can rise to the surface.

But hot spot volcanoes usually look like ellipses going around the land. Many Australian volcanoes are lonely pillars – now standing alone in the middle of nowhere.

“Instead of large eruptions like Krakatoa or Vesuvius, or iconic volcanoes like Mount Fuji, the effect is more like the bubbles appearing as you heat your pancake mix,” says Mather.

Another method may lie in pockets of explosive chemistry.

An accessible mixture of material can respond to the formation of gases that push up through weak parts of the continent, generating volcanoes just like many of those we find across Australia.

It is a strong hypothesis with good evidence to support it, but it leaves the question of where such a mix came from in the first place.

Swarms of molten rock may have been scraped up as one continent slid beneath another, or it may have churned streams in the mantle rubbing from lower parts of the crust. These events could explain several million years of volcanism covering a strip of land just at the knife edge of a sinking piece of bark.

To cover 100 million years of volcanic history, we will need a comprehensive model with living power.

In addition, he also had to outline similar volcanoes that reveal the surface of his underwater neighbor, the ‘lost’ continent of New Zealand.

This volcanic spine actually extends over a 5,000-kilometer (3,100-mile) wide stretch of the Earth’s crust.

He hopes to explain any of these persistent theories.

Fortunately, this period of geological activity is neatly aligned with the sinking of a large stretch of the Pacific plateau far east of Australia, starting at the eastern Tonga-Kermadec Trench and north of New Zealand.

Thousands of kilometers of seabed are slowly moving beneath the Australian continental shelf, dragging with them a rich icing of volatile minerals depleted by marine life, back as dinosaurs stagger around.

“What sets the eastern Australia-Zealand region apart is that the seabed that is pushed beneath the continent from the western Pacific Ocean is full of hydrous materials and carbon-rich rocks,” says Mather. .

“This is creating a movement zone just below Australia’s east coast full of volatile materials.”

The theory explains not only periods of volcanic activity dating back many millions of years, but the extent of their access deep into the interior of the continent.

It is not easy enough to find evidence to support the theory, as we are still receiving adequate coverage of seismic sensors throughout New Zealand and eastern Australia. But the researchers are confident that the data we have is in line with this new model.

Isotopes collected from volcanic rock formations along the coast will also match the types of names that would be expected from thick layers of goats on the ocean floor cooked in the mantle.

“The peaks of volcanic activity connect nicely with the amount of seabed recycling at the Tonga-Kermadec trench east of New Zealand,” says Mather.

It is not just the geological history of Australia that needs explanation; the theory could be used to explain similar areas of activity around the world, including in eastern China and western USA.

It is unclear whether Australia can expect new explosive shapes soon. With a belly full of volcanic batter, his days of geological activity may be long gone.

This research was published in Advances in science.