"Night of the Living Uturuncu" doesn't exactly roll off the tongue. But this dormant volcano in the southwest corner of Boliva has more in common with the walking dead than one might think.
Cornell researchers detected signs of life in the "zombie" volcano, despite it's being ostensibly inactive for more than 250,000 years, by periodically pinging the region with satellite radar two decades ago.
Jennifer Jay, Ph.D. '14 and collaborator Branden Christensen deploy seismometers at Uturuncu during a 2010 field expedition.
After conducting seismology and rock analysis led by researchers from the University of Science and Technology of China (USTC) and University of Oxford, the team has now identified a likely source of the activity: molten rock releasing gas that pushes against Uturuncu's upper crust.
The combination of techniques presents a new way to capture a three-dimensional, CAT scan-like image of subsurface volcanic activity that could help predict eruptions and also potentially identify the location of highly sought-after mineral deposits.
The findings were published April 28 in Proceedings of the National Academy of Sciences.
"When people look at volcanoes, they're like, 'Oh, if it's not going to erupt, we're not interested in it.' But actually volcanoes that look dead on the surface are not dead underneath," said Matthew Pritchard, professor of earth and atmospheric sciences in Cornell Engineering, who led the Cornell team. "There are still processes going on. And the processes in Uturuncu are particularly interesting because they're telling us about the liquids and the gasses that are moving through there that might become, or maybe even today are, a reservoir of minerals that could be useful for technology."
The project began nearly 25 years ago, when Pritchard was a doctoral student at California Institute of Technology. By comparing periodic snapshots taken by satellite radar interferometry, he was able to monitor sub-centimeter changes on the Earth's surface, gaining insights into volcanoes, glaciers, earthquakes - essentially anything that deforms the ground.
While surveying the Andean Mountain range, he found a number of volcanoes widely believed to be inactive. One of them, Uturuncu, near Boliva's border with Chile, had a distinctive shape - not unlike a sombrero - approximately 70 kilometers (43 miles) wide.
"There was uplift in the middle of this place and subsidence in a ring around it," said Pritchard, who also directs the Institute for the Study of the Continents. "It was really a unique sort of bullseye pattern. We were very confused as to what that was."
A field expedition followed in 2009, and over the next three years, Pritchard, his students and his collaborators recorded seismic activity from 48 seismometer stations in the region, which detected more than 1,700 earthquakes. The researchers also measured changes in the gravity field and the natural electrical currents underground, and performed petrological analysis and rock physics modeling.
"You can sort of combine all of those together to help you understand, 'OK, what are the physical properties at these depths of several kilometers that we couldn't otherwise probe.' We couldn't drill down there deep enough to see all of these different features," he said.
The team's analysis revealed pathways of migrating fluids traveling toward the surface and a shallow gas accumulation zone beneath the crater. This magmatic hydrothermal system has been causing the surface to rise by up to 1 centimeter per year.
Understanding this system may help explain how, and where, concentrations of copper and other minerals form.
"The idea is that fluids are flowing through molten rock and they pick up some minerals on their way, and then they take them somewhere and deposit them," Pritchard said. "Even though we're not really worried about this particular volcano erupting in the next few years, we can sort of see in real time the processes of this happening. Clearly there is activity underground that may be even, at some point, economically useful."
Uturuncu maybe be a zombie, but it's not alone. Pritchard's use of satellite radar interferometry has identified similar volcanos around the world that continue to show signs of seismic activity or ground deformation, even though they haven't erupted in hundreds of thousands of years.
"These are sort of unique beasts," he said. "But they're not completely uncommon."
Bolivia has roughly a dozen dormant volcanos, and Pritchard hopes to continue monitoring them - from space and on the ground - in case any of them start to stir.
"Uturuncu might not erupt, but some of its neighbors might," he said.
The paper's lead author is Ying Liu of USTC. Co-authors include Patricia MacQueen, Ph.D. '22; Haijiang Zhang of USTC; Michael Kendall and Jonathan Blundy of University of Oxford; and Thomas Hudson of the Institute of Geophysics, ETH Zurich.
The research was supported by the National Science Foundation; National Environmental Research Council of the UK; National Key Research and Development Program of China; National Natural Science Foundation of China; and the Royal Society. The seismic instruments were provided by the EarthScope Consortium through the EarthScope Primary Instrument Center at New Mexico Tech.
