There could be a large, untapped geothermal resource between Rotorua and Taupō.
The theory comes after years of research by GNS Science and was announced by geophysicist Dr Ted Bertrand to a crowd of 180 to 200 community members at a presentation on Tuesday night.
Bertrand is among a team of three scientists and at least four technicians who have modelled rock types, depths, and temperatures in 366 sites across the Rotorua and Okataina calderas, since 2015, building on previous research started near Taupō in 2009.
They used a technique called magnetotellurics, or MT, in which sensors and cables are placed on the ground and left for two days.
The equipment measures electromagnetic signals in the earth's crust that are a million times weaker than the energy field of an electric fence.
Bertrand said the findings, which have not yet been published, will affect sustainable management of existing geothermal fields, future exploration for new geothermal resources for energy generation, and for management of volcanic hazards.
In short, the results show the association between geothermal and volcanic processes is closer and shallower than previously thought.
Bertrand said this information would be most valuable when combined with information from other sources such as seismology, gravity, geology and geochemistry and Māori matauranga.
"We have not been looking for the needle in the haystack [ideal place for a geothermal plant], we wanted to understand the haystack."
Geothermal energy accounts for 18 per cent of New Zealand's electricity generation.
Dr Bertrand said GNS Science's MT work supported the Government's goal of achieving 100 per cent of electricity generation from renewable sources by 2035.
It currently sits between 90 per cent and 93 per cent.
"MT has played a significant role in increasing the knowledge of the underlying magmatic systems that drive New Zealand's geothermal energy industry."
The Bay of Plenty Regional Council has funded a large part of the project in the Rotorua area.
GNS geophysicist Grant Caldwell said, "It's been a tremendous help".
He said the team had not covered sites under Rotorua lakes, but hoped to in the future.
Deputy mayor Dave Donaldson said the findings were "extremely interesting".
He said it was up to the community to manage geothermal resources sustainably and support tourism and hazard management.
Taupō Volcanic Zone facts
- Rotokawa hosts the world's largest single geothermal turbine
- The Taupō caldera had the world's last super-eruption more than 26,500 years ago when 1000cu km of material was emptied
- In comparison, the Okataina caldera has erupted 80cu km of material in the last 21,000 years, including the 1886 eruption of Mt Tarawera