A “ZOMBIE” volcano could be coming back to life after lying dormant for hundreds of thousands of years.
Ominous rumblings from deep underground made scientists fear that Uturuncu in Bolivia was on the brink of eruption.
The volcano, in the Andes of southwest Bolivia, last spewed lava 250,000 years ago.
It has shown signs of unrest for several decades – including releasing gas and mini earthquakes.
And now scientists think they know why.
A new study published on Monday in the journal PNAS suggests the disturbances have been caused by swirling of liquid and gas beneath the mountain– rather than an explosive magma build-up.
The researches wrote: “This not only explains why a ‘”zombie'” volcano remains active but also offers insights into its eruption potential.”
They added that their research has developed a technique that could be help figure out the risk of other, active volcanoes erupting.
Uturuncu is a whopping dormant volcano in the middle of South America’s barren Andes mountains.
It’s peak towers 6,008 metres above sea level.
Scientists know it as a “stratovolcano”, which is the name for the large, steep, cone-shaped structure.
This formed by layers of lava, volcanic ash and rock repeatedly hardening over the years.
When stratovolcanoes erupt it is often very explosive, because the thick layers of rock trap gas easily.
Mount Vesuvius, which decimated Pompeii, is the most famous example of a stratovolcano.
Satellite and GPS radar show that the area around Uturuncu has been deforming in a “sombrero” pattern since the 1990s.
This involves the central peak rising whilst its surroundings sink.
Uturuncu has been growing upwards at a rate of about 1cm each year, data shows.
This gradual shape-shifting, combined with the frequent earthquakes and gas plumes, led some scientists to believe there was a huge build-up of magma underground.
However, the new study found that – rather than a pressurised build-up of magma – the activity is more likely due to hot fluids and gases being sent up from something called the Altiplano-Puna Magma Body.
This is a deep well of magma that sits beneath southern Bolivia, northern Chile and northern Argentina.
Scientists think this reservoir is releasing expulsions up chimney-like spouts.
These get trapped just below the surface, they believe, and cause some commotion as they break through.
If the deformation and earthquakes are due to fluids and gas sloshing around beneath the surface, on not a sharp rise of magma, the volcano is less likely to erupt – as previously feared.
Co-author Matthew Pritchard, a Cornell University geophysics professor, said: “The methods in this paper could be applied to the more than 1,400 potentially active volcanoes and to the dozens of volcanoes like Uturuncu that aren’t considered active but that show signs of life — other potential zombie volcanoes.”