When the island of Santorini was rattled by thousands of small earthquakes earlier this year, many people were left mystified about the source of the tremors.
The shaking lasted more than a month and forced more than 10,000 people to evacuate the Greek island. At times, the earthquakes occurred every few minutes. The largest reached a 5.3 magnitude.
But University of Oregon geophysicist Emilie Hooft felt less perplexed about the source of the earthquakes, as she had an informed hunch about what was going on.
Just 10 days before the earth started quaking in the Greek islands, Hooft’s lab submitted a paper outlining new discoveries about the volcanic plumbing surrounding Santorini, which offered some important clues about the source of the earthquakes. While some scientists initially assumed they were connected to a tectonic event related to the fault system near Santorini, Hooft’s research suggested they were actually fueled by volcanic unrest deep in the crust.
Namely, the underground magma movement that was transpiring six to nine miles beneath the volcanic system—though, importantly, offset so they were not directly below the volcanoes themselves.
“We found magma at deeper depths that is offset from both the main volcano and from the active volcanic seamount 10 kilometers (6 miles) to the northeast,” Hooft said. “Two Ph.D. students worked with me to probe deeper beneath the volcanic system than any prior efforts and found magma that proved to be the source of a sideways injection of magma deep in the crust, located right where the seismic swarm was initiated.”
Hooft’s lab published two related papers earlier this year in the journal Geochemistry, Geophysics, Geosystems. Both projects grew out of extensive research into the crustal structure of the crust and the magmatic evolution of the Santorini volcanic complex.
In the first paper, doctoral student Beck Hufstetler’s research used sound waves to map out the melt content of the magma system. And in the second, doctoral student Kaisa Autumn used different sound waves to find deep magma deep under the volcanic region, which surprisingly aligned with the location of the seismic activity.
“Because the recent earthquakes weren’t in line with any known volcanic features, other scientists did not immediately recognize them as having a volcanic origin,” Hooft explained. “Our research showed that these earthquakes were not offset from all the known volcanic features; they’re actually sourced right from this deep magma storage region that we discovered.”
Hooft said scientists are increasingly finding evidence that magma is not always located directly under the major, and most visible, mountain of a volcano.
“Our research reinforces a growing view that volcanic unrest shouldn’t be considered in isolation, but as part of a complex, evolving system of magma, fault and crust,” she said. “Magma movement is often guided by structural features of the crust, like cracks in the fault system, which means future volcanic unrest may occur outside traditional volcanic centers.”
Hooft began studying the region in 2015, and led one of the largest seismic imaging projects conducted at a volcano. For nearly a month, the international team of researchers covered around-the-clock shifts to send powerful sound waves through the ocean to collect information about Santorini’s volcanic plumbing.
The sound waves, which are created through canisters of compressed air, function like an ultrasound that can detect what kind of material makes up the volcanic system, including lava, rock and water.
“We were able to probe far under the volcano to really understand the deepest part of the plumbing system of a subduction zone arc volcano,” she said, adding that the research both improved the resolution of the shallow and mid-crust layers, while also imaging deeper into the crust than any prior studies.
The crust is generally around 15 miles thick, and until these two projects, Hooft’s research had been limited to the first three to four miles of the crust.
Hooft’s group was especially interested in understanding how magma moves throughout the entire crust and how it interacts with the fault system beneath volcanoes like those around Santorini. To measure deeper into the more compact part of the crust, Autumn had to use a more advanced method, which involved using reflected sound waves to image the entire crust.
They found that magma was moving in the cracks created by the fault system six to nine miles beneath the surface. Because the cracks are offset from the volcanoes themselves, they’re creating potential pathways for magma to move sideways while remaining underground.
Hooft hopes to keep building on her work in Santorini so she can fill more gaps in the research.
“Understanding how and when magma moves through these systems remains one of the central challenges in volcanic science and a critical step toward detecting early warning signs and improving hazard assessment in vulnerable regions like the southern Aegean,” she said.
More information: R. S. Hufstetler et al, Seismic Structure of the Mid to Upper Crust at the Santorini‐Kolumbo Magma System From Joint Earthquake and Active Source Vp‐Vs Tomography, Geochemistry, Geophysics, Geosystems (2025). DOI: 10.1029/2024GC012022
Kaisa R. Autumn et al, Exploring Mid‐to‐Lower Crustal Magma Plumbing of Santorini and Kolumbo Volcanoes Using PmP Tomography, Geochemistry, Geophysics, Geosystems (2025). DOI: 10.1029/2025GC012170
Journal information: Geochemistry, Geophysics, Geosystems
Provided by University of Oregon