Scientists Solve the Mystery of Bolivia’s “Zombie” Volcano Uturuncu, Geologically Dead but Showing Signs of Activity

An international team of scientists from China, the United Kingdom, and the United States has managed to decipher the internal processes of the Uturuncu volcano in Bolivia, known as the zombie volcano for showing signs of activity despite being considered geologically dead. Using a combination of seismology, physical models, and rock composition analysis, the researchers have identified the causes of its volcanic unrest, dispelling fears of an imminent eruption. The findings, published in the journal PNAS, offer a detailed view of the magmatic system beneath this Andean giant.

Located deep in the central Andes, Uturuncu is a volcano inactive since its last eruption 250,000 years ago. However, in recent decades it has exhibited signs of unrest, such as earthquakes and gas emissions, earning it the nickname “zombie.” In addition, satellites have detected a peculiar ground deformation pattern in the shape of a “hat”: the center of the volcanic system rises while the surrounding areas sink.

For local populations, understanding whether this activity could trigger an eruption—and its potential magnitude—is crucial, given the risk of widespread damage and loss of life. However, until now, there was no clear explanation of what was driving this anomalous activity. The key, according to the scientists, lay in visualizing the movement of magma and gases beneath the surface.

zombie volcano bolivia — Cerro Uturuncu, one of many volcanoes on the Bolivian Altiplano that lie above the Altiplano-Puna Magma Body. Credit: Jon Blundy / University of Oxford

The new study, the result of collaboration between the University of Science and Technology of China, the University of Oxford, and Cornell University, used signals from more than 1,700 seismic events to produce high-resolution images of the magmatic “plumbing” system in the shallow crust beneath Uturuncu. The results indicate that the volcano’s activity is due to the movement of fluids and gases beneath the crater, with minimal likelihood of it leading to an eruption in the short term.

Volcanic systems are complex networks of fluids and gases stored in magmatic and hydrothermal reservoirs. Previous studies had already established that Uturuncu sits atop the largest known magma body in Earth’s crust: the Altiplano-Puna Volcanic Complex. It was also known that an active hydrothermal system connects this magmatic reservoir to the surface. But how fluids circulated through this underground system remained a mystery.

To solve it, the team used seismic tomography, a technique that allows scientists to visualize the volcano’s interior similarly to how a CT scan images the human body. Since seismic waves travel at different speeds depending on the material they pass through, this method provided detailed three-dimensional images of Uturuncu’s internal structures.

Combining these data with analyses of the physical properties of rocks, the researchers identified possible pathways for geothermally heated fluids to rise, and how these liquids and gases accumulate in reservoirs just beneath the crater. According to the study, this process is responsible for the ground deformation, and at the same time suggests that the risk of an eruption is low.

Professor Mike Kendall, co-author of the study and member of the Department of Earth Sciences at the University of Oxford, emphasized: Our results show how combined geophysical and geological methods can enhance our understanding of volcanoes, their hazards, and the potential resources they hold.

Professor Haijiang Zhang, of the University of Science and Technology of China, highlighted the key role of multidisciplinary collaboration: Only thanks to the expertise of the team were we able to integrate advanced geophysical imaging tools with models of rock properties and their interaction with fluids.

Professor Matthew Pritchard, of Cornell University, added that the methodology used could be applied to more than 1,400 potentially active volcanoes around the world, as well as others similar to Uturuncu that, while not considered active, show signs of life: other possible zombie volcanoes, in his words.

With this discovery, Uturuncu is no longer a threatening mystery but rather a case study that could set a precedent in global volcanology. For now, Bolivia can breathe easy: its “zombie volcano” remains asleep.

SOURCES

University of Oxford

Y. Liu, J.M. Kendall, H. Zhang, J.D. Blundy, M.E. Pritchard, T. Hudson, & P. MacQueen, Anatomy of the magmatic–hydrothermal system beneath Uturuncu volcano, Bolivia, by joint seismological and petrophysical analysis, Proc. Natl. Acad. Sci. U.S.A. 122 (18) e2420996122, doi.org/10.1073/pnas.2420996122