Revealing volcanic plumbing

Understanding the plumbing systems that lie under volcanoes could help scientists predict large scale eruptions, but observing them can be difficult since 98% of the global mid-ocean ridge is below sea level.

However, two new studies looking at mid-ocean ridges in Afar (Ethiopia) and Iceland – the only places where the ridges appear above sea level – reveal new information about where magma is stored and how it moves through the geological plumbing network.

Scientists used images taken Envisisat – a European Space Agency satellite – to measure how the ground moved before during and after eruptions. Using this data they were able to build and test computer models to find out how rifting – where tectonic plates pull apart and new magma injects itself into weaknesses in the brittle crust – occurs.

The research showed the existence of elongated, shallow magma chambers beneath fast-spreading mid-ocean ridges was well established, but at slow-spreading ridges, such chambers were less evident. However, one study showed that magma chambers that fed an eruption in November 2008 in the Afar ridge were only 1km below the ground – the standard model predicted a depth of 3km.

“It was a complete surprise to see that a magma chamber could exist so close to the Earth’s surface in an area where tectonic plates move apart so slowly,” said Dr Carolina Pagli, lead author from the University of Leeds. “The results have changed the way we think about volcanoes.”

The magma chamber was divided into two segments and the eruption triggered by a small influx of magma into the northern segments. Both segments fed the main eruption through a connecting dyke and have been rapidly refilling since.

Pagli also noticed that the ground started uplifting four months before the eruption due to new magma increasing the pressure in one of the underground chambers – understanding these precursors is key to predicting eruptions.

A wider study of eruptions in Afar and Iceland were remarkable similar and researchers identified multiple magma chambers position horizontally and vertically allowing magma to shoot in several directions.

“The dramatic events we have been witnessing in Afar in the last six years are transforming our understanding of how the crust grows when tectonic plates pull apart,” said Dr Tim Wright. “Our work in one of the hottest places on Earth is having a direct impact on our understanding of eruptions from the frozen volcanoes of Iceland.”

• Geophysical constraints on the dynamics of spreading centres from rifting episodes on land
• Shallow axial magma chamber at the slow-spreading Erta Ale Ridge