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The Reykjanes Peninsula at Iceland's southwestern edge is one of the country's most populated regions, and it is also one of the most volcanically active. In 2024, sensing technology developed at Caltech was deployed in the region to study the motion of subsurface magma and its eruption into lava on the surface.

Using data from the technology, called distributed acoustic sensing (DAS), researchers developed a method to provide warnings up to 30 minutes in advance of lava eruptions. The study shows that DAS can be a useful tool to both study volcanic activity and provide early warnings to the public.

The research was conducted in the laboratory of Zhongwen Zhan (Ph.D. '13), professor of geophysics and the Clarence R. Allen Leadership Chair and director of the Caltech Seismological Laboratory. A paper describing the study was in the journal Science on April 24.

Since November 2023, the Reykjanes Peninsula has experienced eight eruptions of lava, some of which were large enough to threaten towns. While Iceland itself is relatively volcanically active, researchers theorize that this particular area may be entering into a yearslong period of increased activity.

To study this, Zhan and his team developed a collaboration with Icelandic scientists and the telecommunication company Ljósleidarinn to deploy the DAS sensors in the peninsula for a year with the aim of better characterizing volcanic activity and developing an eruption early-warning system.

"The deployment was extremely fast," says Jiaxuan Li, the study's first author and a former postdoctoral scholar at Caltech who is now an assistant professor at the University of Houston. "We were able to set up our system on a 100-kilometer-long fiber cable within 10 days after a substantial magma intrusion event on November 10, 2023. About a month later, we recorded the first eruption with our system. This was a major international collaboration with real-world impact."

DAS works by pointing lasers into unused underground fiber-optic cables (like those that provide internet). As vibrations pass through the cable, whether they are from an earthquake or the rumblings of traffic, the laser light experiences a so-called phase change. Measuring the phase change in this laser light gives researchers information about the passing waves, making a 100-kilometer cable equivalent to a line of thousands of conventional seismic sensors.

Volcanic activity also causes underground deformations: The ground stretches and compresses as magma pushes up from shallow underground chambers, where it sometimes builds enough pressure to erupt to the surface through cracks called dikes. DAS can precisely measure underground movement on the order of millimeters in real time, a much higher resolution than GPS or satellite imaging.

Over the year of the study, DAS collected data on underground volcanic activity, monitoring how the Earth stretches in real time as magma moves around. From this data, the team developed a preliminary early-warning system that gave the public between 30 minutes to several hours of advance notice before an eruption, depending on the nature of the magma intrusion.

Seismologist Vala Hjörleifsdóttir of Reykjavik University, a co-author of the study, had been working in Iceland to devise an eruption early-warning method. In particular, an active eruption site near the town of Grindavik was posing a threat to the town's several thousand inhabitants. When the Caltech team set up the DAS sensors, Hjörleifsdóttir collaborated with them to identify signals in the data that indicated an eruption was coming.

"One day, in August 2024, we were in a group meeting at Caltech and my phone started going off with the early warning alert," Li says. "Twenty-six minutes later, Vala emailed us that the eruption had actually happened and that they had sent out an evacuation warning."

"This is the most active volcanic system in Iceland," Zhan says. "In addition to the need to provide advance warnings before an eruption, the project is scientifically interesting because we saw more magma intrusion events there than we originally thought—ones that don't come up to the surface.

"There is a lot more work to do, and all volcanoes are different, but DAS provides us a new capability to see things we couldn't before. Our project is also a great example of the power of international collaboration."