New understanding of how magma moves underground

Using the most extensive dataset ever gathered from a volcanic eruption, an international team of researchers have developed a model of how huge magma-filled cracks form underneath volcanic systems and how they spread. The researchers, including scientists from the University of Cambridge, will use the results to help predict how molten rock moves underground, and whether or not it erupts.

A volcanic eruption in the Holuhraun area of central Iceland has now lasted over 100 days, with no end in sight. The eruption has received widespread attention and scientists have followed the activity closely since its onset at the Bárðarbunga central volcano.

Using GPS geodetic measurements and interferometric analysis of satellite synthetic aperture radar images, and earthquake observations, a team of scientists, including researchers from the University of Cambridge, has constructed a model for the formation of a huge magma-filled crack, or dyke, in late August 2014. Details are published today (15 December) in the journal Nature.

The dyke stretches for more than 45 kilometres, from the Bárðarbunga central volcano to the Holuhraun site, where magma has been erupting since the summer.

The dyke mostly formed in the two weeks before the main eruptive activity began. Its average opening is approximately 1.5 metres wide, focused from just beneath the surface to six kilometres down. The dyke volume grew to 0.5 cubic kilometres before the main eruption began. A model for the dyke also explains the unusual and varying direction of dyke segments that relate to interaction of topography and stresses in the ground caused by divergent plate movements in Iceland.

The rate of the dyke’s spread slowed as the magma reached natural barriers, leading to a build-up of pressure, which eventually broke through the barrier and created a new segment of crust. The results show how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at such divergent plate boundaries.

“This is probably the best-documented eruption ever,” said Professor Bob White of Cambridge’s Department of Earth Sciences, who used up to 70 broadband seismometers to monitor activity around Bárðarbunga and Holuhraun.

The team hopes that similar studies could be carried out in near real time to improve understanding and ability to forecast the evolution of lateral dykes in various tectonic settings.

The team of researchers, coordinated by the University of Iceland, also included researchers from the Icelandic Meteorological Office and eight universities in other countries. The research is part European research project FUTUREVOLC funded by the European Union.