Natural Hazards Commission Toka Tu Ake say signs of heat under the Auckland area’s largest volcano could provide vital insights into the after-effects of an eruption. 

Researchers have found solidified magma beneath the Rangitoto Island volcano that is hot enough to fuel a hydrothermal system.   

The volcano, which last erupted more than 600 years ago, is about 10km from Auckland’s city centre.   

It is the first time heat has been detected in the region’s volcanic field, but the University of Auckland’s Alutsyah Luthfian, who led the study, says it doesn’t mean the volcano is active or nearing an eruption.   

“While we had expected the unerupted magma under the volcano to be solidified, we were really surprised that it is still warm enough to heat groundwater and drive a weak hydrothermal system 600 years later,” Mr Luthfian said.   

He says more information can now be gathered about the possible impacts of an eruption.  

“With this new data point, we can potentially map a curve of how heat disperses with time and better predict the long-term environmental and societal impacts of eruptions from Auckland’s larger volcanoes like Rangitoto,” he said.   

“Our work suggests that ... the ground under and near a new volcano may stay warm for at least decades after a future eruption, impacting how Aucklanders could start to rebuild, work and live near the newly formed volcano.”   

NHC chief resilience officer Jo Horrocks says the study provides an important insight into “how a major eruption in Auckland might play out and heat its surroundings for many years after the fact. It’s important to invest in research in Auckland’s volcanoes, so we can know which signs to look for and prepare for the impacts from a volcanic eruption.”