A rediscovered volcanic crater under a central Auckland suburb will help scientists predict what could happen if a volcano forms in the region in future.
Scientists analysing records from boreholes drilled for the foundations of buildings and roads have identified the 1km wide crater.
The Grafton volcano was last recorded on a map dating back to 1859, but its whereabouts has been forgotten in intervening years.
The volcano, filled with solidified lava flows, is estimated to be between 80,000 to 100,000 years old.
Geologist Bruce Hayward says he rediscovered the volcano by accident after finding an adjacent lava flow at the Domain and believes there are now about 50 volcanoes in the Auckland region.
Volcanologist Jan Lindsay says studies of the Grafton volcano will form part of a wider project on the Auckland volcanic field, ranging from geological studies through to what impact any future volcanic eruption would have on society.