Hotspot volcanoes

Australia was once home to hundreds of ancient volcanoes. We can finally find out why


Geologically, Australia is a relatively quiet place to live. Earthquakes are rare and typically sweet, and as with volcanoes, there has not been as much as a burp of magma on the continent in thousands of years.

It hasn’t always been that way. In fact, the earth is littered with the remains of mysterious eruptions that have shattered the crust with surprising regularity over the past 80 million years.

A new study suggests that some of the more unusual spells of activity were the result of an ancient seabed creeping under the plate, providing the perfect paste for a vast cycle of eruptions across the length of the continent.

Sheer cliffs of Cradle mountain in Tasmania at the famous Victoria’s Organ pipes, at the dramatic heights of Glass house mountains in Queensland, an impressive array of monoliths line Australia’s east coast like a twisted spine.

What provoked them is not at all obvious.

“We are not on the famous Pacific ‘ring of fire’ that produces so many volcanoes and earthquakes. ” said geoscientist Ben Mather of the University of Sydney.

“So we needed another explanation why there were so many volcanoes on the east coast of Australia.”

In many parts of the world, far from the edges of any tectonic plate, volcanoes are the product of rising heat that burns the crust. As the crust slides over areas of high temperature, weaknesses can channel ascending magma to the surface.

Still hot spot volcanoes tend to look like ellipses dotting the landscape. Many Australian volcanoes are lonely pillars, isolated in the middle of nowhere.

“Rather than huge explosions like Krakatoa or Vesuvius, or iconic volcanoes like Mount Fuji, the effect is more like the bubbles that emerge when you heat your pancake mix.” said Mather.

An alternative mechanism could lie in pockets of explosive chemistry.

Mixtures of volatiles can react to form gases that rise through weak parts of the continent, generating volcanoes like many found in Australia.

It’s a solid hypothesis with good evidence to back it up, but leaves open the question of where these mixtures might come from in the first place.

Perhaps eddies of molten rock dredged them as one continent slid under another, or perhaps eddies in the mantle erased the lower parts of the crust. These events could explain millions of years of volcanism covering a strip of land just flush with the knife with a sinking piece of crust.

To cover 100 million years of volcanic history, we will need a large and sustainable model.

In addition, one should also explain similar volcanoes dotting the surface of its submarine neighbor, the “lost” continent of Zealandia.

This volcanic “backbone” actually stretches across a 5,000 kilometer (3,100 mile) wide section of the earth’s crust.

None of the current theories has the hope of explaining all of this.

Fortunately, this vast period of geological activity aligns perfectly with the sinking of much of the Pacific Plate far east of Australia, starting with the Tonga-Kermadec Trench to the east and north. from New Zealand.

Thousands of miles of seabed are slowly pushed beneath Australia’s continental shelf, bringing with them a rich icing of volatile minerals deposited by marine life during the days when dinosaurs trampled.

“What distinguishes the region of eastern Australia and Zeeland is that the seabed pushed under the continent from the western Pacific is highly concentrated in hydrous materials and carbon-rich rocks”, a- he added. said Mather.

“This creates a transition zone just under the east coast of Australia which is enriched with volatiles.”

The theory explains not only periods of volcanic activity stretching back millions of years, but the extent of its reach deep within the continent.

Finding a lot of evidence to support the theory is not easy, as we have yet to obtain adequate coverage from seismic sensors across Zealandia and eastern Australia. But the researchers are confident that the data we have is consistent with this new model.

Isotopes collected from volcanic rock formations along the coast also match the types of signatures expected from the thick layers of goop on the ocean floor being cooked in the mantle.

“The peaks of volcanic activity correlate well with the amount of seabed recycled in the Tonga-Kermadec trench in eastern New Zealand”, said Mather.

It is not only the geological history of Australia that calls for an explanation; the theory could be used to explain similar fields of activity around the world, including eastern China and western United States.

It is not known if Australia can expect further explosive formations in the near future. With a belly full of volcanic paste, its days of geological activity may be far from over.

This research was published in Scientists progress.