A huge "zombie" volcano in Bolivia is showing signs of life, but scientists say, thankfully, that there is little immediate risk of an eruption.
Uturuncu, a towering peak in the Central Andes, last erupted around 250,000 years ago.
Yet for decades, researchers have observed unusual activity – including small earthquakes and a distinctive ‘sombrero’ pattern of ground deformation, with the centre of the volcano slowly rising while the surrounding area sinks.
Until now, the cause of this unrest remained unclear.
A new study published in the journal PNAS reveals that heated liquids and gases are still migrating beneath Uturuncu, creating pockets of pressure that deform the surface.
Using seismic data from more than 1,700 earthquakes, an international team of researchers from China, the UK and the US produced the most detailed three-dimensional image yet of the volcano’s underground structure.
They found that fluids are rising from the Altiplano–Puna magma body, a vast reservoir of partially molten rock buried deep beneath the Andes.
As these fluids ascend through a narrow vertical pathway, they accumulate just below the volcano’s summit, forming reservoirs of gas and brine. This fluid migration, rather than new injections of magma, appears to be driving Uturuncu’s ongoing activity.
“Our results show how linked geophysical and geological methods can be used to better understand volcanoes, and the hazards and potential resources they present,” said Prof Mike Kendall from the University of Oxford, a co-author of the study.
Crucially, the researchers found that the amount of gas stored underground is relatively low, meaning the chances of a major eruption are currently small.
While the findings should reassure local communities, they also highlight the need for vigilance. Uturuncu is one of dozens of zombie volcanoes around the world: systems that are officially dormant but still showing signs of internal movement.
"The methods in this paper could be applied to the more than 1,400 potentially active volcanoes,” said co-author Prof Matthew Pritchard from Cornell University. "And to the dozens of volcanoes like Uturuncu that aren't considered active but that show signs of life – other potential zombie volcanoes."
For now, Uturuncu slumbers on, restless beneath the surface, but not quite ready to wake up just yet.
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