Engineering, Environment and Sustainability

CRL links Auckland to its volcanic past

Construction of the City Rail Link (CRL) in Auckland has uncovered a link to the region’s pre-historic past.

A tree fragment uncovered during tunnel boring has been dated to 28,000 years ago.

The fragment was found when CRL’s small tunnel boring machine, Jeffie, was excavating for a stormwater drain under Mt Eden. The machine was tunnelling through an ancient lava field 15 metres below ground.

After being extracted from the site, the tree fragments were sent to volcanologists for radiocarbon dating. This confirmed that Maungawhau/Mt Eden erupted roughly 28,000 years ago, said Elaine Smid volcanologist at DEVORA.

“We have used other techniques to date this eruption, with similar findings. This new radiocarbon result removes any lingering doubts about the age of Maungawhau/Mt Eden.”

The finding allows for scientists to confirm that Mt Eden erupted during the Ice Age, and connects the current rail tunnelling program to similarly significant geological events in Auckland’s past, said Gabriel Kirkwood Kaitiaki for Ngāi Tai ki Tāmaki – Taiaomaurikura.

“Both events in their own way are creating dramatic changes to the landscape of Tāmaki Makaurau and the way we interact with it for generations to come,” said Kirkwood.

The tunnelling is part of excavations to connect CRL tunnels with Auckland’s existing rail network at Mt Eden. While the CRL will enable Aucklanders to travel around their city without the need to get into cars, the excavation has helped in other ways to keep Auckland safe, said Smid.

“DEVORA scientists use volcano ages to identify eruption patterns and to better understand how the Auckland Volcanic Field has behaved in the past – it’d like a big puzzle,” she said.

“This age is another piece in that puzzle, now slotted firmly into place. Every piece we add tells us a little more about how the volcanic field may behave in the future, making Auckland a safer place.”

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