Volcanic activity better understood after Bolivian expedition

A magmatic lake 15km below a dormant volcano in Bolivia may explain how and why volcanoes erupt.

A team of international researchers discovered a large body of water dissolved into partially molten rock beneath Cerro Uturuncu. This relationship - between silicate melt (magma) and water - is believed to be a factor in volcanic eruptions.

Professor Jun Blundy, from the School of Earth Sciences at Bristol University, said: “Silicate melt (magma) can only dissolve water at high pressure; at lower pressure this water comes out of the solution and forms bubbles. Crucially - these bubbles can drive volcanic eruptions.”

Tests were carried out at the University of Orléans based in France to better understand the partially dissolved rock found in Bolivia, where researchers discovered eight to ten percent of water was dissolved in the magma. This also had the side effect of increasing the electrical conductivity of the magma.

Professor Bundy, said: “This is a large value. 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 magmatic lake is estimated to have an amount of water at least one and a half million km³, equivalent to some of the world’s largest freshwater lakes, such as Lake Superior.

Professor Fabrice Gaillard, from the University of Orléans, and co-author said: “Ten percent by weight of dissolved water means that there is one molecule of water for every three molecules of silicate. This is an extraordinarily large fraction of water, helping to explain why these silicate liquids are so electrically conductive."

The international group of researchers included scientists from Germany, France, Iceland and Wales. They hope that better understanding of this phenomenon can improve predictions of when eruptions will happen. The study was published in Earth and Planetary Science Letters.