Fears of an imminent volcanic eruption in Bolivia have been alleviated by researchers from the University of Oxford.
A team from the Department of Earth Sciences, in collaboration with the University of Science and Technology of China and Cornell University, have been studying Bolivia's 'zombie' volcano, Uturuncu.
By combining seismology, physics models, and rock composition analysis, they have identified the causes of Uturuncu's unrest and concluded an eruption is unlikely.
Having last erupted 250,000 years ago, Uturuncu is technically dead, but was dubbed a 'zombie' volcano because it still shows signs of unrest, including earthquakes and gas plumes.
This unrest causes a 'sombrero' pattern of deformation, with the land in the centre of the volcanic system rising and the surrounding areas sinking.
For the local population, it is crucial to assess the potential start and severity of an eruption from Uturuncu, which could cause widespread damage and threat to life.
However, until now, there was no explanation for the continued volcanic unrest.
The new study used signals detected from more than 1,700 earthquake events to perform high-resolution imaging of the plumbing system in the shallow crust beneath the volcano.
According to the findings, the unrest of Uturuncu is due to the movement of liquid and gas beneath the crater, with a low likelihood of an imminent eruption.
Previous studies have shown Uturuncu sits above the world's largest known magma body in the Earth's crust, the Altiplano-Puna Volcanic Complex, and that an active hydrothermal system connects this body and the surface.
However, it was unknown how fluids may be moving through this underground system.
The research team used seismic tomography, a way of imaging the interior of the volcano, similar to methods used in medical imaging of the human body.
Seismic waves travel at different speeds through different materials, thereby providing insights into the inner workings of Uturuncu in three dimensions.
They combined this with analysis of the physical properties of the system, including rock composition, to better understand the volcanic system.
This analysis picked out possible upward migration pathways of geothermally heated fluids and showed how liquids and gases accumulate in reservoirs directly below the volcano's crater.
The research team believe this is the most likely cause for the deformation in the centre of the volcanic system, and the risk of a real eruption is low.
Co-author Professor Mike Kendall, from the University of Oxford, said: "I am very pleased to be involved in this truly international collaboration.
"Our results show how linked geophysical and geological methods can be used to better understand volcanoes, and the hazards and potential resources they present."
