Auckland University scientists say Aucklanders may have to live with a continuously erupting volcano on their doorstep in future.
Their findings are based on analysis of volcanic debris from the bed of Lake Pupuke near Rangitoto Island and have been published in the Journal of Volcanology and Geothermal Research.
Scientists previously believe Rangitoto Island formed in two large eruptions about 500 years ago.
Phil Shane says his team discovered the volcano actually erupted nearly continuously over a 1000 year period, finishing in the 16th century with two big explosions.
He says that means planners need to rethink volcanic risk assessments for Auckland City.
"We wouldn't like to go as far as saying that it will erupt again but what it tells us is at least the youngest volcano in Auckland erupted for a long time," he said.
Dr Shane says if there is future volcanic activity, whether near Rangitoto or at another location, it is possible it would go on for a long time.
He says there may have been eruptions from Rangitoto more recently than 500 years ago but human activity has disrupted younger sediments in lake bed and he plans to do more work to discover more accurately when the volcano stopped erupting.