Chamber accumulates off the main volcanic zone, raising questions about volcano hazards.
New Zealand geologists have discovered a magma chamber being born in a surprising place — not under the country’s most active volcanoes, but off to one side.
The finding suggests that molten rock can accumulate underground in complex and unexpected patterns. No eruption is imminent, however.
“There’s no need to panic, but chances are there are lots of bodies of magma dotted throughout the crust,” says Ian Hamling, a geophysicist at GNS Science in Lower Hutt, New Zealand. He and his colleagues describe the discovery on 3 June in Science Advances1.
His team uses radar data from satellites, such as the European Space Agency’s now-defunct Envisat, to study ground motions in the Taupo volcanic zone. This region, in the central part of New Zealand’s North Island, has seen 25 enormous eruptions in the past 1.6 million years. Today it is home to some of the country’s most spectacular volcanic features, from the bubbling hot pots of Rotorua to eruptions at White Island, most recently in April.
A 2015 study found that much of the main Taupo volcanic zone was subsiding, or sinking, as expected when magma erupts from underground2. But one blob , along the north and west coasts of the Bay of Plenty , appeared to be rising. “I just discounted it at the time, because we were so focused on looking at the more volcanic part,” says Hamling.
Later the team took a closer look , including data from ground-positioning stations as well as geodetic surveys dating back to the 1950s. They found the ground rising about 5 to 6 millimeters a year at first , but that rate doubled to about 12 millimeters a year starting in the mid-2000s. It has since dropped back to the lower rate.
Calculations suggest that about 9 million cubic metres of magma — about 3,600 Olympic swimming pools’ worth — pushed into the crust each year during peak growth. It would have gathered in a mushy chamber about 10 kilometres deep. “When you compare it to other places, like Yellowstone, we’re smaller than that,” Hamling says. “But it’s still pretty significant.”
The city of Tauranga, with more than 100,000 residents, lies about 50 kilometres west of the uplift. Elaine Smid, a volcanologist at the University of Auckland, notes that people in the area are already at risk of volcanic hazards, especially ashfall from the neighbouring Taupo volcanoes. The new work underscores the need for people to stay on top of the latest science, she says.
The New Zealand discovery adds to other examples around the world, including in the central Andes and in Africa, where magma seems to be pushing into the crust in places other than active volcanoes, says Matthew Pritchard, a geophysicist at Cornell University in Ithaca, New York. He calls them “zombie volcanoes,” showing signs of life when they should be dead.
“Not to be too glib, but we are not undergoing a zombie volcano invasion,” he says. Rather, researchers can see more ground movements than they ever could before, thanks to the sharp vision of radar satellites.
Hamling’s team wants to do a more detailed study of the area, using different techniques to probe the size and shape of the newfound magma chamber.
Hamling, I. J., Hreinsdóttir, S., Bannister, S. & Palmer, N. Sci. Adv. 2, e1600288 (2016).
Hamling, I., Hreinsdóttir, S. & Fournier, N. J. Geophys. Res. Solid Earth 120, 4667-4679 (2015).
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Witze, A. Magma slides stealthily beneath New Zealand. Nature (2016). https://doi.org/10.1038/nature.2016.20023