Mysterious underground lake could teach us about volcanic eruptions

Researchers have discovered a large underground lake of water and molten rock under a dormant volcano that could reveal new details about volcanic eruptions, according to a new study in the journal Earth and Planetary Science Letters.

Discovery of the liquid body, determined to have a temperature of nearly 1,000 degrees Celsius (1,832 degrees F), has led researchers to wonder if very similar bodies of water could be ‘hiding’ under other volcanoes. The study team said it could also help clarify why and how volcanoes erupt.

“The Bolivian Altiplano has been the site of extensive volcanism over past 10 million years, although there are no currently active volcanoes there,” study author Jon Blundy, an earth scientist from the University of Bristol, said in a news release. “This anomaly has a volume of 1.5 million cubic kilometers (360,000 cubic miles) or more and is characterized by reduced seismic wave speeds and increased electrical conductivity.”

Finding a Strange Lake

The study team said the properties they observed indicated the presence of molten rock, along with liquid water.

“The rock is not fully molten, but partially molten,” Blundy said. “Only about 10 to 20 percent of the rock is actually liquid; the rest is solid. The rock at these depths is at a temperature of about 970 degrees Celsius (1778 degrees F).”

The study team used high temperature and pressure tests to assess the electrical conductivity of the molten rock in the underground lake and determined that there must be approximately 8 to 10 percent of water blended in the silicate melt.

“This is a large value,” Blundy said. “It agrees with estimates made for the volcanic rocks of Uturuncu using high temperature and pressure experiments to match the chemical composition of crystals.

The researchers noted that silicate melt is only capable of dissolving water at high pressure. At lower pressures, water comes out of the solution and forms bubbles that can drive volcanic eruptions.

“The 8 to 10 percent of water dissolved in the massive anomaly region amounts to a total mass of water equivalent to what is found in some of the giant freshwater lakes of North America,” Blundy said.

“This is an extraordinarily large fraction of water, helping to explain why these silicate liquids are so electrically conductive,” said study author Fabrice Gaillard, from the University of Orléans in France.

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Image credit: Jon Blundy

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