A team of researchers has discovered an enormous reservoir of water mixed with magma, or semi-molten rock, roughly nine miles beneath Uturuncu, a dormant volcano in the Andes.

In an article published in the journal Earth and Planetary Science Letters, the scientists say there that there may be many lakes deep in the Earth beneath other volcanoes as well, and that the bodies of water may explain how and why eruptions happen. The lakes also may play a role in the formation of the Earth's crust.

The subterranean lake apparently contains a volume of water that's somewhere between Lake Huron (850 cubic miles) and Lake Superior (2,903 cubic miles), according to Jon Blundy, a volcano researcher and professor at the UK's University of Bristol, who was one of the study's authors.

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According to New Scientist, Blundy and colleagues discovered the massive lake while investigating the Altiplano-Puna magma body, an even more massive underground formation that slows down seismic waves and conducts electricity.

The researchers took rocks ejected by an eruption of Uturuncu that occurred half a billion years ago, mixed them with water in the lab and then subjected them to pressure and temperature conditions comparable to those deep in the Earth. They found that with a mix of about eight to 10% water, the electrical conductivity matched the actual Altiplano-Puna.

That data matched other formations that have been discovered beneath volcanoes such as Mount St. Helen's in Washington state, which led the researchers to suspect that such bodies of water could be a common feature of the areas underneath volcanoes.

Blundy told New Scientist that the water mixed with magma may explain the composition of rocks in the Earth's continental crust. When the magma - which is mostly composed of basalt - rises up from the Earth's mantle, the hot layer below the crust, the water helps enrich the basalt with silica and depletes magnesium. That eventually forms rocks such as andesite, a fine-grained igneous rock.

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The water mixed with magma also helps to form bubbles, "which can end up as an explosive eruption," Blundy told the British science publication.

Better understanding the role of water in eruptions may help scientists to understand seismic activity better and improve their predictions of volcanic events, Blundy said.

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