Under every volcano is a complex web of tunnels, chasms, magma pockets, and connections between. How they interact may lead to knowledge of how a volcano performs and erupts. 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 the location and behavior of magma chambers on the Earth's mid-ocean ridge system - a vast chain of volcanoes along which the Earth forms new crust. They worked in Afar (Ethiopia) and Iceland - the only places where mid-ocean ridges appear above sea level. Volcanic ridges (or spreading centers) occur when tectonic plates rift or pull apart. Magma (hot molten rock) injects itself into weaknesses in the brittle upper crust, erupting as lava and forming new crust upon cooling.
Magma chambers work like plumbing systems, channeling pressurized magma through networks of underground pipes. crevices or tunnels.
A magma chamber is a large underground pool of liquid rock found beneath the surface of the Earth. The molten rock in such a chamber is under great pressure, and given enough time, that pressure can gradually fracture the rock around it creating outlets for the magma. If it finds a way to the surface, then the result will be a volcanic eruption; consequently many volcanoes are situated over magma chambers. Magma chambers are hard to detect, and most of the known ones are therefore close to the surface of the Earth, commonly between 1 km and 10 km under the surface. In geological terms this is extremely close to the surface, although in human terms it is considerably deep underground.
The studies, published in Nature Geoscience, reveal new information about where magma is stored and how it moves through the geological plumbing network. Finding out where magma chambers lie and how they behave can help identify early warning signs of impending eruptions.
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 magma chambers that fed an eruption in November 2008 in the Afar rift of Northern Ethiopia were only about 1 km below the ground. The standard model had predicted a depth of more than 3 km.
It is highly unusual for magma chambers to lie in shallow depths on slow spreading centers such as the Afar rift, where tectonic plates pull apart at about the same speed as human fingernails grow.
Dr Carolina Pagli from the University of Leeds' School of Earth and Environment, who led the study, says: "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."
Dr Pagli also noticed that the ground started "uplifting" (elevating) four months before the eruption, due to new magma increasing pressure in one of the underground chambers. Understanding these precursory signals is fundamental to predicting eruptions.
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.
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 centers. Most spreading centers are under 2 km of water at the bottom of the ocean, making detailed observations extremely challenging.
For further information: http://www.leeds.ac.uk/forstaff/news/article/3088/volcanic_plumbing_exposed
Photo: James Hammond