Six centuries after Rangitoto erupted, scientists have found the magma beneath the island is still hot enough to drive a hidden hydrothermal system, giving Auckland a rare look at how the land might behave after a future eruption.

Rangitoto, sitting just 10km from the city centre, is the largest and youngest of the 53 volcanoes that make up the Auckland Volcanic Field.

Lead researcher Alutsyah Luthfian (Fian) from the University of Auckland says it’s the first time signs of heat from volcanic activity have been detected in the field.

“We expected the unerupted magma to be fully solidified, but were surprised to find it still warm enough to heat groundwater, even after 600 years,” Fian explains.

For Coasties, this matters because Auckland’s next eruption won’t just bring lava and ash — the land could stay hot for decades afterwards.

That could affect rebuilding, underground services, and how people live around a new volcanic cone.

Researchers point to Heimaey, Iceland, where slowly cooling lava powered homes for 15 years.

The findings are part of the long-running DEVORA programme, funded by Auckland Council and the Natural Hazards Commission.

Using simple clay pots and wire, the team tracked voltage signals that confirmed circulating warm groundwater under Rangitoto, with gas readings adding another layer of evidence.

Dr Jo Horrocks, Chief Resilience Officer at NHC, says this work helps prepare Auckland for the long-term impacts of an eruption, not just the event itself.

And for now, Rangitoto’s gentle silhouette on the horizon is just a reminder of how much life here is shaped by the land beneath our feet.

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