Geothermal systems occur in many parts of New Zealand. High temperature geothermal fields are principally located in the Taupo Volcanic Zone, with another high temperature field at Ngawha in Northland. Moderate to low and very low temperature systems are more widely scattered. Some are associated with areas of young volcanism: in Northland, Hauraki Plains, and the coastal Bay of Plenty. Many hot springs, particularly in the South Island, are associated with faults and tectonic features.
By the 1980s it was believed that all of New Zealand’s high temperature geothermal resources had been identified, a situation that few other countries can claim even today. Of New Zealand’s 129 identified geothermal areas, fourteen are in the 70-140ºC range, seven in the 140-220ºC range and fifteen in the >220ºC range.
The Taupo Volcanic Zone extends from White Island in the Bay of Plenty southwest to Mt Ruapehu. Geothermal fields are associated with young and active rhyolitic volcanism. Magma intruded into the stretched and fractured crust of the zone has resulted in temperatures of at least 350ºC at depths of less than 5 km. This has provided a huge heat source from which geothermal systems have developed and been sustained for periods of up to hundreds of thousands of years. A total of 29 geothermal areas have been identified, although only about half of these have potential for resource utilisation. Individual fields are typically about 12 sq km in area and spaced 15 km apart, and include all those in New Zealand that discharge boiling water.