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By Felix Walton of 

New research on Rangitoto is helping scientists plan for what might happen if Auckland’s biggest volcano erupts.

University of Auckland researchers have discovered that the hardened magma below Rangitoto is still warm 600 years after it formed.

The report was led by PhD student Alutsyah Luthfian and assisted by associate geophysics professor Mila Adam.

“We found signs of a hidden hydrothermal system beneath Rangitoto that was unknown for us,” Adam said.

“We were measuring natural electric signals in the subsurface and they showed us a specific pattern that tells us there are circulating waters. The only way this could be happening is if the water is warm and interacting with the colder water that comes from the sea.”

Researchers deduced the water was being warmed by the solidified magma.

“It’s solid, but it’s hot, so as water comes in contact, it gets warmed up and that makes it circulate,” she said. “There are studies worldwide that have seen similar signals, such as Izu-Oshima in Japan and Stromboli in Italy.”

Mila Adam said magma was understood to take a significantly long time to cool, but the results of this research were still surprising.

“What was new for us was we really thought 600 years was long enough,” she said. “We don’t see surface manifestations, there is all this beautiful forest on Rangitoto, but in reality, there is still hot water beneath it.”

Adam squashed any fears that the geothermal activity could signal an eruption.

“It’s telling us Rangitoto is a bit more active than we thought,” she said. “Nothing to be worried about, definitely nothing that would be a precursor to an eruption, but it’s less dormant than we thought.

“It’s still quite alive in terms of a hydrothermal system and CO2 emissions.”

The data would help scientists prepare for that eventuality, she said.

“After an eruption, you would of course have the whole landscape destroyed, the vegetation and all the people affected. We can use this data to model how long it will take the magma to cool and therefore the ability of a location to regenerate [after an eruption],”

“There’s definitely lots of potential to understand what a future eruption does.”

- RNZ