Underneath a town in New Zealand, a new volcano might very slowly be growing.
Such was the suggestion inferred from a previously unknown magma chamber discovered by a team of scientists in the coastal town of Matata, which is about 120 miles southeast of Auckland.
Researchers say the huge magma chamber could also explain the recent swarm of earthquakes that shook the town in recent years. Although experts do not expect drastic events or an eruption anytime soon, they say the chamber contains enough magma to fill 80,000 Olympic-sized swimming pools.
Ian Hamling, lead author of the report and a geophysicist from GNS Science, says there is no need to panic. However, it is likely that lots of bodies of magma are "dotted" throughout the crust.
What was remarkable about the study is that there are no active volcanoes near Matata. He says it is quite unusual to detect magma in an area where there are no volcanoes.
"It was quite a big surprise," says Hamling.
Thanks to modern equipment, the researchers were able to accurately measure horizontal and vertical changes in the coastal land.
Hamling and his colleagues at GNS Science investigated ground motions in the Taupo Volcanic Zone (TVZ) by using radar data from different satellites, including data from the defunct Envisat of the European Space Agency.
The TVZ runs down the center of North Island in New Zealand, which has seen 25 massive eruptions in the past 1.6 million years. Today, the region possesses spectacular volcanic features, such as bubbling hot pots and frequent eruptions at Whakaari.
Previous studies have found that much of the TVZ was sinking or subsiding, which is anticipated because magma drains from an underground chamber.
However, one area to the west along the Bay of Plenty coast appeared to be rising, researchers say. Hamling says at that time, they dismissed it because they were focused on looking for volcanic features.
The team did take a closer look later. They took in data from global positioning stations and geodetic surveys that dated back from the 1950s.
Scientists found that the ground near Matata had risen by 5 millimeters (0.19 inches) per year in the 1950s, but that the growth rate doubled to about 12 millimeters (0.47 inches) per year beginning in the mid-2000s. It has since dipped back to the lower rate, they said.
Link To Earthquakes
A period of sudden rise in the land between 2004 and 2011 most likely generated thousands of small earthquakes, which scientists previously thought were caused by tectonic shifts. Hamling says the quakes are also likely triggered by magma stressing and breaking rock.
The magma remained 6 miles below the surface, which is deep enough that Hamling says it wouldn't develop into a volcano within his lifetime. The volcano could either rise after hundreds or thousands of years, or the magma chamber would eventually cool and harden.
Meanwhile, researchers say their findings would allow them to develop a warning signal for the town of Matata, which has a population of 650 people.
Details of the study are featured in the journal Science Advances.