Uturuncu, the highest mountain in southwestern Bolivia, caused a region near its summit—about 150 kilometers (93 miles) wide—to rise and fall, creating a sombrero-like shape.
Over 1,700 recent earthquakes have prompted scientists to study Uturuncu.
By integrating satellite data, seismic analysis, and computer models of rock behaviour under pressure, researchers have gained a clearer understanding of the internal workings of Uturuncu, uncovering the cause of its unusual activity.
Their findings were published on April 28 in the Proceedings of the National Academy of Sciences.
Volcanic eruptions generally happen when magma rises into underground pockets known as magma chambers and escapes through vents or fissures to the surface.
The eruptions tend to be more violent when the magma is thicker, as it traps gases that build up pressure, which is then released explosively, sending magma shooting out as lava.
However, this isn’t the case beneath Uturuncu, as the study reveals. Instead, magma, gases, and briny fluids are interacting within a hydrothermal system—an activity not entirely understood—to cause the volcano’s “zombie” rumblings.
Beneath Uturuncu, at depths ranging from 10 to 20 kilometres (6 to 12 miles), lies the Altiplano-Puna Magma Body, a vast magma reservoir spanning about 200 kilometres (124 miles).
It is the largest known active magma body in the Earth’s crust. Previous studies suggested an active hydrothermal system linking this magma reservoir to the mountain above, but the precise interaction between magma and fluids remained unclear.
The study revealed that as the magma body heated underground liquids and released gases, these fluids and gases moved upwards, collecting in chambers beneath the crater.
This movement triggered seismic activity, released steam, and caused the volcano’s rock to deform, leading to a surface rise of approximately 1 centimetre (0.4 inches) annually.
While these internal processes explain Uturuncu’s activity, the study suggests that the “zombie” volcano is unlikely to erupt anytime soon.
Dr. Mike Kendall, coauthor of the study and professor at the University of Oxford, reassured that there are no alarming signs. “We’re not seeing seismicity increasing or migrating from great depths, which would indicate magma movement,” he explained. “It seems the volcano is simply releasing gas and calming down.
The Global Volcanism Program has tracked about 50 “zombie” volcanoes, ranging from 12,000 to 2.6 million years old, mostly showing geothermal features like hot springs and fumaroles.
Uturuncu, along with others, could help identify those at risk of eruption. Some have higher surface temperatures and are explored for geothermal energy and mineral deposits.
“Many still require further investigation,” says Dr. Matthew Pritchard from Cornell University. “Some may be cooling, while others might increase in activity,” he adds.