When the volcanic island of Santorini experienced a protracted series of tremors earlier this year—culminating in a 5.3-magnitude quake that prompted the evacuation of more than 10,000 residents—many observers attributed the seismic unrest to tectonic faulting in the southern Aegean. However, a recent study led by University of Oregon geophysicist Dr. Emilie Hooft reveals that the quakes were in fact driven by deep magma injection, providing fresh insights into the island’s volcanic plumbing and improving forecasts of future volcanic hazards.
Unprecedented Seismic Swarm Raises Alarm
Beginning in late February 2025, the tranquil waters surrounding Santorini gave way to an abrupt burst of seismic activity. Over the course of more than a month, small tremors rattled homes nearly every few minutes, unsettling both residents and scientists. The frequency and intensity of the quakes intensified gradually, peaking with a magnitude-5.3 event that rocked coastal villages and forced the Hellenic authorities to undertake one of the largest evacuations in Greek modern history.
Initial speculation pointed toward a tectonic origin, given the network of fault lines that crisscross the Hellenic arc. Yet the spatial clustering of the earthquake hypocenters—6 to 9 miles (10 to 15 kilometers) beneath the seafloor, and offset laterally from the main volcanic edifices—hinted at a deeper, volcanic driver.
Imaging the Volcanic “Plumbing System”
Just ten days before the tremors commenced, Dr. Hooft’s lab had submitted two groundbreaking papers to the journal Geochemistry, Geophysics, Geosystems that mapped the deep crustal architecture beneath Santorini using seismic reflection techniques. Unlike prior studies that probed only the upper 3–4 miles of crust, Hooft and her team deployed compressed-air sound-wave sources—functioning analogously to medical ultrasound—to image the entire ~15-mile-thick crust.
Graduate students Kaisa Autumn and Beck Hufstetler spearheaded the data collection, firing canisters of compressed air from research vessels and arraying seismometers across the bay. The sound waves penetrated deep into the crust, reflecting off boundaries between rock, magma, and water, thereby revealing hidden channels, reservoirs, and fracture networks.
Discovery of Deep, Offset Magma Reservoirs
Analysis of the seismic profiles uncovered a startling feature: a large body of molten rock 6–9 miles beneath the surface, situated not directly beneath the island’s active volcanic cones but displaced approximately 6 miles (10 kilometers) to the northeast, near the site where the seismic swarm began. This reservoir lay within a network of faults—ancient fractures that, under renewed stress, opened just enough to permit lateral magma movement deep in the crust.
“We found magma at deeper depths that is offset from both the main volcano and from the active underwater seamount to the northeast,” explained Dr. Hooft. “This sideways injection of magma provided the perfect mechanism to trigger the earthquake swarm—magma migrating through faults, building pressure, and creating tremors as it forced its way into new fractures.”
Magma-Driven Quakes vs. Tectonic Faulting
The distinction between tectonic and magmatic origins is more than academic. Tectonic earthquakes result from the abrupt release of strain along pre-existing faults, while magmatic quakes arise as molten rock intrudes into the crust, fracturing and deforming solid rock. The latter often precede volcanic eruptions, serving as potential early warning signals.
In Santorini’s case, the recorded depths and the spatial correlation with the newly imaged magma body strongly favor a magmatic interpretation. “Although tectonic motion undoubtedly occurs in this region,” said Autumn, “the swarm’s depth and geometry align precisely with where we imaged the deep magma reservoir. It was a eureka moment.”
Implications for Volcanic Hazard Assessment
Santorini—a volcanic complex with its last major eruption in 1950—poses a perennial hazard to the densely populated islands and mainland communities of the southern Aegean. Understanding how magma moves through this intricate plumbing system is essential for forecasting future unrest and issuing timely alerts.
“Detecting sideways magma injections at these depths is a critical step toward identifying early warning signs of potential eruptions,” Dr. Hooft noted. “If we can monitor pressure changes or volumetric shifts in this deep reservoir, we may gain precious weeks or months to prepare for surface manifestations.”
Such monitoring could involve periodic seismic surveys, deployment of deep borehole strainmeters, and continuous GPS measurements to capture subtle ground deformations. Integrating these data streams with established networks of surface seismometers and gas-emission sensors would create a comprehensive early warning system.
Advances in Seismic Reflection Techniques
Key to the breakthrough was the expansion of seismic reflection methods—long established in the oil and gas industry—into volcanic research. Hooft’s team adapted the technology to marine environments, synchronizing compressed-air sources with ocean-bottom seismometers to obtain high-resolution images of the entire crustal thickness.
“These sound-wave surveys allowed us to see deeper and clearer than ever before,” said Hufstetler. “We resolved interfaces between different rock types and detected magma pockets that had eluded previous studies.”
Notably, the research improved the resolution of both shallow and mid-crustal layers while penetrating beyond 15 kilometers depth. This dual capability—delineating near-surface fractures and deep magma pathways—opens new avenues for investigating subduction-zone volcanoes worldwide, from Indonesia to the Pacific Northwest.
Next Steps: Expanding the Research
With the connection between deep magma injection and the earthquake swarm now established, Hooft’s group plans to extend their investigations across the southern Aegean arc. Additional seismic campaigns will target neighboring volcanic centers—such as Milos, Nisyros, and Kos—to ascertain whether similar deep reservoirs exist and occasionally reactivate.
“By mapping these systems comprehensively, we can better understand the distribution of magma storage regions and their interactions with tectonic faults,” Hooft said. “Each volcano has its own plumbing history, but the processes governing magma migration are universal. Our methods can be applied to any arc-volcanic region.”
Furthermore, the team aims to refine their imaging techniques by incorporating three-dimensional seismic tomography and combining reflection data with magnetotelluric surveys, which measure electrical conductivity in the subsurface. Such multidisciplinary approaches promise even greater clarity.
Community Engagement and Hazard Mitigation
Recognizing the human dimension of volcanic hazards, the researchers collaborate closely with Greek civil protection agencies, local universities, and municipal authorities on Santorini. Through workshops and data-sharing platforms, they ensure that scientific findings translate into actionable emergency plans, evacuation procedures, and resilient infrastructure designs.
Local emergency manager Eleni Papadopoulou praised the partnership: “Dr. Hooft’s work has given us a deeper understanding of our volcano’s behavior. By incorporating these insights into our hazard maps and public-education programs, we can protect lives and reduce disruptions when the volcano next awakens.”
Conclusion: A Milestone in Volcanic Science
The study led by Emilie Hooft and her graduate students represents a milestone in volcanic geophysics. By illuminating the deep conduits through which magma travels—and demonstrating their direct role in seismicity—the research reshapes how scientists perceive and prepare for volcanic crises. As the Aegean’s iconic islands face a future of ongoing tectonic and magmatic interplay, these insights offer a pathway to safer, more informed communities.
“Understanding how and when magma moves through these systems remains one of the central challenges in volcanic science,” Dr. Hooft concluded. “Our research on Santorini brings us one step closer to unraveling that mystery—and to delivering the early warnings that vulnerable regions so desperately need.”
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