Geophysicist Ian Hamling said that since 1950, enough magma to fill 80,000 Olympic-size swimming pools has squeezed up beneath the surface near the coastal town of Matata, about 200 kilometers (120 miles) southeast of Auckland.
A paper published Saturday in the online journal Science Advances outlines the findings. Hamling, the paper’s lead author, said that while other parts of New Zealand have active volcanoes, there have been none near Matata for at least 400,000 years.
“It was quite a big surprise,” he said in an interview with The Associated Press.
Using GPS data and satellite images, the scientists say they discovered an area of land about 400 square kilometers (154 square miles) has risen by 40 centimeters (16 inches) since 1950.