Massive 'Lake' Found 15 Km Under a Volcano

Scientists have discovered a huge magmatic lake, 15 km below a dormant volcano in South America, a finding that could unlock why and how volcanoes erupt. The body of water – which is dissolved into partially molten rock at a temperature of almost 1,000°C – is the equivalent to what is found in some of the world’s giant freshwater lakes, such as Lake Superior. The finding by researchers from University of Bristol in the UK and colleagues has led scientists to consider if similar bodies of water may be ‘hiding’ under other volcanoes and could help explain why and how volcanoes erupt. The Bolivian Altipano has been the site of extensive volcanism over past 10 million years, although there are no currently active volcanoes there. The Altipano is underlain by a large geophysical anomaly at depths of 15km below the surface of Earth. This anomaly has a volume of one and a half million cubic kilometres or more and is characterized by reduced seismic wave speeds and increased electrical conductivity. This indicates the presence of molten rock. The rock is not fully molten, but partially molten. Only about 10 to 20% of the rock is actually liquid; the rest is solid. The rock at these depths is at a temperature of about 970°C. In order to characterize the partially molten region, the team performed high temperature and pressure experiments. This measured the electrical conductivity of the molten rock in the ‘anomalous’ region and concluded that there must be about eight to 10% of water dissolved in the silicate melt. Silicate melt can only dissolve water at high pressure; at lower pressure this water comes out of the solution if form of bubbles. Crucially, these bubbles can drive volcanic eruptions.