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Volcanic plumbing exposed

30 March 2012, by Adele Rackley

Two new studies into the 'plumbing systems' that lie under volcanoes could bring scientists closer to predicting large eruptions.

International teams of researchers, led by the University of Leeds, studied magma chambers on the Earth's mid-ocean ridge system – a vast chain of volcanoes along which the Earth forms new crust.

Lava lake

The Erta Ale lava lake at the Afar rift

They worked in Afar, Ethiopia, and Iceland – the only places where mid-ocean ridges appear above sea level. Volcanic ridges, or spreading centres, are caused by tectonic plates rifting, or pulling apart. Molten rock, or magma, then pushes into weaknesses in the brittle upper crust, erupting as lava and forming new crust when it cools.

It's a bit like a plumbing system, with pressurised magma moving through networks of underground 'pipes'.

The studies, published in Nature Geoscience, reveal new information about where magma is stored and how it moves through this geological plumbing, which can help identify early warning signs of impending eruptions. In fact the scientists detected that the ground at Afar started 'uplifting' four months before an eruption in 2008, due to new magma increasing pressure in one of the underground chambers.

Scientists used images taken by the European Space Agency satellite Envisat to measure how the ground moved before, during and after eruptions. Using this data, they built and tested computer models to find out how rifting occurs.

Data in one study showed that the magma chambers that fed an eruption in Afar in November 2008 were only about 1 km below the ground. The standard model had predicted a depth of more than 3 km. The scientists also detected that the ground at Afar started 'uplifting' four months before the eruption, due to new magma increasing pressure in one of the underground chambers.

It is highly unusual for magma chambers to lie in shallow depths on slow spreading centres such as the Afar rift, where tectonic plates pull apart at about the same speed as human fingernails grow.

'It was a complete surprise to see that a magma chamber could exist so close to the Earth's surface in an area where the tectonic plates move apart so slowly. The results have changed the way we think about volcanoes,' says Dr Carolina Pagli from the University of Leeds' School of Earth and Environment, who led the study.

A wider study of eruptions in Afar and Iceland, two vastly different environments, found remarkable similarities. Many events occurred within a short space of time. Researchers identified multiple magma chambers positioned horizontally and vertically, allowing magma to shoot in several directions. Moving magma triggered earthquakes, and separate magma chambers fed single eruptions.

The 2008 eruption is part of an unusual period of recent volcanic unrest in Ethiopia, and is enabling scientists to learn more about volcanoes at spreading centres. Most spreading centres are under 2 km of water at the bottom of the ocean, making detailed observations extremely challenging. The new knowledge derived from Ethiopian volcanoes will help scientists understand volcanoes in Iceland, where eruptions can have a bigger impact on the UK.

'The dramatic events we have been witnessing in Afar in the past six years are transforming our understanding of how the crust grows when tectonic plates pull apart. Our work in one of the hottest place on Earth is having a direct impact on our understanding of eruptions from the frozen volcanoes of Iceland,' says Dr Tim Wright from the School of Earth and Environment, who leads the international Afar Rift Consortium.