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A wave from our past

Chris Hollis takes a look into the past in the rocks at Tora. PHOTOS/ GRACE PRIOR

Tora, one of Wairarapa’s best-kept secrets and known by locals for its wild scenery has been hiding something else – evidence that a goliath tsunami swept across New Zealand after an asteroid crashed into the Earth’s atmosphere, killing most of the dinosaurs. GRACE PRIOR reports.

TIMES-AGE EXCLUSIVE

For more than 60 million years, Tora has kept the tsunami secret to itself. Now, a team of researchers spread across the globe has found proof the massive wave existed.

The discovery was the culmination of Carterton geologist Dr Chris Hollis’ life’s work.

At the end of the Cretaceous period, about 66m years ago, the Chicxulub asteroid impact near the Yucatan peninsula of Mexico produced a global tsunami 30,000 times more energetic than any modern-day earthquake-generated tsunami.

The Yucatan peninsula is about 12,000 kilometres from Tora’s shores, but a lead researcher from the University of Michigan, Molly Range,said the site held the “most telling confirmation” of the global significance of the catastrophic event.

Harvard University researchers said in a 2021 report that the asteroid left behind a crater off the coast of Mexico spanning close to 150km in diameter and pushing about 20km deep.

Hollis has his finger on the evidence of a mega-tsunami triggered by the Chicxulub asteroid.

The asteroid’s impact brought an end to the reign of the dinosaurs, triggering a mass extinction, along with the demise of almost three-quarters of all plant and animal species then living on Earth.

Hollis and his team’s modelling found that one hour after the meteor hit, the tsunami had spread outside the Gulf of Mexico and into the North Atlantic. Four hours after impact, the waves had passed through the Central American Seaway and into the Pacific.

A day later, the waves had crossed most of the Pacific from the east and most of the Atlantic from the west and entered the Indian Ocean from both sides.

Within two days, significant tsunami waves reached most of the world’s coastlines.

Hollis said the asteroid triggered at least one to two years of total darkness and raging wildfires, but the tsunami was, until recently, unknown.

“The current thinking is that the global darkness only needed to last a year or two to kill the plants, although they may have come back through seeds. It was enough to kill off all the herbivores.

“Once they died, eventually all the major carnivores would die as well.”

The report modelled the first 10 minutes of the event with what it called a crater impact model.

It found that the Chicxulub tsunami tumbled into most coastlines of the North Atlantic and South Pacific with waves more than 10 metres high and approached shorelines at a speed of more than one metre per second.

“The tsunami was strong enough to scour the seafloor in these regions, removing the sedimentary records of conditions before and during this cataclysmic event in Earth history and leaving either a gap in these records or a jumble of highly disturbed older sediments,” the report said.

The study focused on “boundary sections,” marine sediments deposited just before or just after the asteroid impact and the subsequent K-Pg mass extinction, which closed the Cretaceous Period.

Hollis said he had been studying the K-Pg boundary for most of his two-decade career, dwelling on the exposure boundary seen in Tora’s rock, with its unique and visibly distorted bedding. Lumps of limestone were uplifted rather than lying flat like the other layers in the rock.

Exploring the craggy shoreline at Tora. “There’s always a story in a rock.”

Hollis was contacted by a University of Michigan professor who had asked about some old research done by the University of Canterbury.

The research suggested some of the sections of rock at Tora could have been shaped by a tsunami, making it a “tsunami deposit”.

“At that point, I was about to tell Ted Moore [the professor] that we had done a lot more work on the section since the work had been published and we were thinking along the same lines.”

Previously, it had been thought that the uplifted rocks were the result of earthquakes along the Hikurangi Subduction Zone to the east of New Zealand.

Moore told Hollis his researchers were doing a study that suggested the Chicxulub tsunami would have had an impact on New Zealand, and with that, Hollis joined the team.

Hollis said the research and writing process was rigorous – Range had finished her master’s degree in 2018, and the paper was only now being published.

He said for years he couldn’t quite wrap his head around the relationship between a sub-marine channel system near Tora and the start of the K-Pg boundary.

“I guess the thing about this paper is that it’s such an obvious thing to have happened when you think about it. If a 14km diameter rock is going to hit the earth in the sea, then surely there is going to be a massive tsunami. I guess it’s a case of where it’s going to go.”

Hollis said the proof was a “eureka moment” that made everything fall into place.

“There’s always a story in a rock,” Hollis said.

Grace Prior
Grace Prior
Grace Prior is a senior reporter at the Wairarapa Times-Age with a keen interest in environmental issues. Grace is the paper’s health reporter and regularly covers the rural sector, weather, Greater Wellington Regional Council, and coastal stories.

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