Did material from lake-making Taupō ‘super-eruption’ reach Australia?

Lake Taupō essentially fills the hole left by the monstrous Ōruanui eruption which occurred around 25,600 years ago. Photo / Peter Wilton

Scientists think they’ve discovered the first evidence of volcanic glass making its way from a New Zealand eruption to Australia - more than 2500km away.

And the big blow in question might’ve been the cataclysm that formed the giant crater today filled by Lake Taupō.

The Ōruanui “super-eruption” at Taupō volcano, some 25,600 years ago, was estimated to have been 100-fold larger than the 1991 eruption of Mt Pinatubo in the Philippines.

In all, about 1170 cubic kilometres of material was blown out, carpeting much of Aotearoa in thick ash while cooling the global climate for a year afterward.

Now, scientists believe tiny shards of glass they unearthed from deep within Tasmania’s Yellow Marsh likely stemmed from the prehistoric event.

Called cryptotephra, the shards and the geochemical signatures locked within them acted like time capsules, offering scientists a unique window into our fiery past.

Using spores found at the same depth, the researchers dated the shards to around 27,600 years before the present.

Because that timing didn’t match precisely with the well-dated Ōruanui event, the scientists turned to other candidates, including eruptions in nearby Australia, and further afield in Papua New Guinea and the Philippines.

After those blows similarly didn’t align, the focus shifted back to Ōruanui, to which the buried shards showed a strong geochemical connection.

As some of the shards displayed an unusual composition, with lower silica and higher iron content, the researchers surmised they might have originated from a less common phase of the eruption.

“I’d stress that the correlation is highly likely but not 100% confirmed, so the geochemical correlation and dating results must be regarded with some uncertainty,” said Victoria University lecturer Dr Jenni Hopkins, who led the study just published in the journal Quaternary Science Reviews.

As for the 1000-year age discrepancy, the team proposed some theories.

One was that the spores used for dating may have been redistributed within the marsh during periods of drying and erosion, leading to an older-than-expected radiocarbon date.

Another one, though less likely, was the shards might point to a previously unknown volcanic event.

Researchers observe pyroclastic flow deposits on the side of State Highway 1, near Taupō, which mark prehistoric volcanic surges that knocked down trees and burned them to charcoal. Photo / Colin Wilson

In any case, the implications for science were exciting.

“These findings confirm what previous studies have speculated on - that volcanic glass from New Zealand can make it to Australia,” Hopkins said.

“It also allows the potential for correlating sediment records between Australia, New Zealand and Antarctica - which is very exciting in terms of global climate reconstructions for this time period.”

Eruptions the scale of Ōruanui are extremely rare: it’s among just a few dozen ever to have topped the eruption-measuring Volcanic Explosivity Index.

Despite a recent year-long unrest period at Taupō, there are no signals pointing toward a blow there any time soon - let alone a super-eruption.

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.

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