Intrusion triggering of the 2010 Eyjafjallajökull explosive eruption

Illustration by Zina Deretsky, U.S. National Science Foundation

Jill Sakai Zina DeretskyFreysteinn Sigmundsson, and Kurt L. Feigl

MADISON – Months of volcanic restlessness preceded the eruptions this spring of Icelandic volcano Eyjafjallajökull, providing insight into what roused it from its centuries of slumber.

An international team of researchers analyzed geophysical changes in the long-dormant volcano leading up to its eruptions in March and April 2010. In a study published in the Nov. 18 issue of the journal Nature, the scientists suggest that magma flowing beneath the volcano may have triggered its reawakening.

“Several months of unrest preceded the eruptions, with magma moving around downstairs in the plumbing and making noise in the form of earthquakes,” says study co-author Kurt Feigl, a professor of geoscience at the University of Wisconsin-Madison. “By monitoring volcanoes, we can understand the processes that drive them to erupt.”

Freysteinn Sigmundsson, lead author on the peer-reviewed paper, has been working in collaboration with Feigl and colleagues from Iceland, Sweden, and the Netherlands for over two decades, watching more than a dozen active volcanoes in Iceland as they deform, using a combination of satellite imaging and GPS surveying. In their Nature paper, they found that Eyjafjallajökull swelled for 11 weeks before it began to erupt in March 2010. The eruption culminated 18 years of intermittent unrest — but no eruptions.

“If you watch a volcano for decades, you can tell when it’s getting restless,” Feigl says.

Eyjafjallajökull had shown similar signs of stirring in 1994 and 1999. In late summer 2009, a subtle shift at a GPS station on Eyjafjallajökull’s flank prompted the study’s lead author, Freysteinn Sigmundsson, and his colleagues to begin monitoring the mountain more closely. Then, in early January 2010, the rate of deformation and the number of earthquakes began to increase. As the deformation and seismic unrest continued, the researchers installed more GPS stations near the mountain. Just a few weeks later, the instruments detected more rapid inflation, indicating that magma was moving upwards through the “plumbing” inside the volcano.

By the time the volcano began to erupt on March 20th, the volcano’s flanks had expanded by more than six inches as magma intruded into the dike and sill structures, as shown in the illustration.

Surprisingly, the rapid deformation stopped as soon as the eruption began. In many cases, volcanoes deflate as magma flows out of shallow chambers during an eruption. Eyjafjallajökull, however, maintained basically the same inflated shape through mid-April, when the first eruption ended.

After a two-day pause, the volcano began to erupt again on April 22nd. This time, the lava broke out through a new vent under the ice-capped summit of the mountain. This second eruption exploded as gas escaped from bubbles in the magma, fragmenting the rock into tiny particles, called “tephra”. Aggravating the explosion, steam blew out of the vent as hot lava melted a pathway through the ice in a matter of days. The resulting plume rose high into the atmosphere, disrupting air traffic over Europe for weeks and stranding millions of travelers.

Why did Eyjafjallajökull erupt when it did? The geologic processes that trigger an actual eruption are not yet well understood, says Feigl. “We‘re still trying to figure out what wakes up a volcano.”

To begin to answer this question, the scientists suggest that magmatic intrusions deep within the volcano started the processes leading to the eruption. “It was the meeting of two different magma types, one residing under the summit area, and another in the evolving intrusion, that triggered the explosive eruption, ” says Sigmundsson.

They are currently studying the structures inside the volcano, such as magma chambers and intrusive conduits, by extracting information from the sensors installed around Eyjafjallajökull.

“The explosiveness of the eruption depends on the type of magma, and the type of magma depends on the depth of its source,” Feigl says. “We’re a long way from being able to predict every eruption, but if we can visualize the plumbing inside the volcano, then we’ll improve our understanding of the processes driving volcanic activity.”

Satellite radar images were obtained from TerraSAR-X, a satellite mission operated by the German Space Agency (DLR) since 2007. Funding for the scientific response to the 2010 eruption was provided by a RAPID grant from the U.S. National Science Foundation, as well by the Icelandic Research Fund, the University of Iceland, and the Icelandic government.

The paper, including a complete list of authors, is available from Nature (

A podcast interview with Freysteinn Sigmundsson is available at

Photos of the effusive flank eruption are available at:

Photos of the explosive summit eruption are available at:

Other data concerning the eruption are available at:

Reports of earthquake activity are available at:

Volcanic Ash Advisory graphics issues by the London VAAC are available at:

Co-author Paul Einarrsson says that “Eyjafjallajökull is not a difficult word” at

Illustration by Zina Deretsky (U.S. National Science Foundation)

Illustration by Zina Deretsky, U.S. National Science Foundation

Artist’s conception illustrating the three-dimensional geometry of the plumbing (left) and timing of events (right column) at Eyjafjallajökull volcano in Iceland. The complicated plumbing inside the volcano consists of inter—connected conduits, sills, and dikes that allow magma to rise from deep within the Earth. The first three panels in the time series show distinct episodes of magmatic intrusions that caused measurable deformation and seismic events in 1994, 1999, and in the first several months of 2010. No eruptive activity occurred during this period of unrest. Each intrusive episode inflated a different section of the plumbing, drawn and modeled as sills at approximately 5 km depth. The fourth panel illustrates the first eruption, between 20 March and 12 April 2010, when basaltic magma (orange) erupted onto the Earth’s surface on the flank of the mountain. The fifth panel shows the second eruption, between 14 April and 22 May, when a different type of magma (trachyandesite, shown in red), erupted explosively at the ice-capped summit (1600 m elevation). The interaction of magma and ice initially increased the explosive activity, generating a plume of particles that rose as high as the 30,000-foot flight level and disrupted air traffic across Europe for weeks.