Ash buried in Antarctica puts date on Taupō supervolcano’s last big blow

A study has linked far-flung deposits in Antarctica to Taupō's last known major eruption, while also helping to refine the date at which it took place. Photo / Peter Wilton

Ash found buried deep in Antarctic ice has highlighted the massive eruptive power of New Zealand’s best-known super-volcano - while also helping scientists refine the date of Taupō's most recent big blow.

That eruption, some 1800 years ago, was one of the largest and most powerful known to have occurred in the past 5000 years - devastating an area of about 20,000 kilometres and spreading volcanic fallout throughout the region.

“But exactly when the eruption occurred has sparked debate,” said Victoria University PhD candidate Stephen Piva, lead author of a study just published in the journal Scientic Reports.

“Our discovery of seven geochemically unique volcanic glass shards buried deep within an ice core confirms the likely timing of the eruption in late summer or early autumn in the year 232.”

The volcanic glass shards were found at a depth of 279m in the Roosevelt Island Climate Evolution ice core, taken from West Antarctica.

Analysis of the geochemical make-up of the shards linked them to the Taupō eruption.

Researchers were then able to assess how long the shards had been there based on the modelled age of the ice layers.

“Ice cores provide invaluable records of the past,” Piva said.

“Finding and fingerprinting volcanic debris trapped in the ice allows us to date when the eruption occurred because we can link it to the modelled age of the ice.”

Of the seven shards, one was a match for volcanic glass produced by Taupō's Ōruanui super-eruption about 25,500 years ago - and which left a giant hole today partly filled by Lake Taupō.

That event, which would have left much of the country carpeted in thick deposits of ash, was so large that it was estimated to have dwarfed the climate-cooling 1991 eruption of Mt Pinatubo in the Philippines by around 100 times.

It’s thought to have sent more than 1100 cubic kilometres of pumice and ash into the atmosphere, compared with the more than 120 cubic km of pumice and ash estimated to have been ejected in 232, when glass from the Ōruanui event would have been unearthed, with fragments finding their way to Antarctica.

The other six shards had a similar geochemical composition that researchers considered could be confidently linked to the Taupō eruption itself.

Lake Taupō effectively fills part of the crater created by the Oruanui super-eruption around 25,500 years ago,

“Combined, the seven shards provide a unique and undeniable double fingerprint of the Taupō volcano as the source,” Piva said.

Detecting the glass shards in Antarctica, which is about 5000 km away from Taupō, showed the power of the eruption.

“A massive eruption plume would have sent a huge volume of volcanic particles into the air where they would have been widely dispersed by the wind,” he said.

“Confirming the eruption date provides an opportunity to study the volcano’s potential global effects on the atmosphere and climate, which is crucial for better understanding its eruptive history and behaviour.”

The study comes soon after a year-long period of unrest at Taupō that prompted GeoNet to raise the volcano’s alert level for the first time in the agency’s history.

Source / GNS Science

It also follows a series of fascinating insights into Taupō's explosive history.

In one paper published earlier this year, Piva and colleagues drew on samples unearthed from an ancient Auckland basin to find that, despite its size, the Ōruanui event didn’t appear to have triggered a long-term global cooling event.

In another 2019 study, scientists modelled potential impacts from a future Taupō eruption, finding that the largest ones could be expected to blanket most major towns and cities in the North Island with tens of centimetres of ash.

But while Taupō was capable of massive destruction, over its history, it had more commonly produced smaller eruptions which had less of an impact.

Scientists have estimated that, over the past 12,000 years, there’d been at least 25 eruptions from Taupō spanning three to four orders of magnitude in size – and most of the smaller eruptions were of a similar size or smaller than the 1980 Mt St Helen’s eruption.

Even these smaller blows remained relatively rare occurrences at the volcano: of 17 unrest episodes in the past 150 years, none have ended with a big event.

“Super-eruptions” like Ōruanui, meanwhile, were incredibly uncommon, even in a global sense: but four of the 10 recorded in the past 2.8 million years have happened in the Central North Island.

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.