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New Zealand sits on the 'largest volcanic outpouring' on Earth, researchers discover

A group of geophysicists at Victoria University of Wellington have used seismic wave-speeds to reveal part of an ancient volcanic "superplume" beneath New Zealand.

Victoria University of Wellington geophysicists Professor Tim Stern and Associate Professor Simon Lamb, together with colleagues, used seismic wave-speeds to reveal part of an ancient volcanic “superplume” beneath New Zealand.

Professor Tim Stern and associate professor Simon Lamb, together with colleagues, believe the North Island sits on part of the "largest volcanic outpouring" on Earth.

They say it was created by an upwelling in the Earth’s deep interior - an event which happened about 120 million years ago when a giant plume of hot rock detached itself from the core-mantle boundary about 3000 kilometres below the Earth’s surface and rose rapidly to the surface as "a superplume".

Findings from professor Stern and associate professor Lamb, both from the School of Geography, Environment and Earth Sciences, has been published today in United States journal Science Advances.

The findings come at a time when professor Stern says the geological community had been close to rejecting the idea of plumes altogether.

"Direct evidence for their existence has been elusive, but with this study we now have both hard evidence that such plume activity did indeed occur and also a fingerprint method to detect fragments of the largest plumes of all–superplumes–rising up from near the Earth’s core.

"In the 1970s, geophysicists proposed that the Earth’s mantle was undergoing a churning motion, rather like a lava lamp, and hot blobs of buoyant rock rose up as plumes from as far as the Earth’s core. Melting of this rock near the surface could then be the cause of prolific volcanism, such as that observed in Iceland or Hawaii," professor Stern says.

"Even larger volcanic outpourings have happened in the geological past, of which the biggest known occurred in the southwestern Pacific in the Cretaceous Period during the time of the dinosaurs, forming a continent-sized underwater volcanic plateau.

"Subsequently, the motion of the tectonic plates broke up this plateau, and one fragment– today forming the Hikurangi Plateau—drifted away to the south and now underlies the North Island and also the shallow ocean offshore."

Professor Stern and colleagues studied the speed of seismic waves (vibrations) through these rock layers to determine their origins and features.