A major volcanic crisis in the Aegean Sea has revealed a previously unconfirmed underground connection between the famous Santorini volcano and the nearby submarine Kolumbo volcano. A new study details how a massive magma intrusion in 2025, which triggered over 30,000 earthquakes, was fed from a reservoir beneath Kolumbo after a period of swelling at Santorini, demonstrating a complex, coupled system.
The event provides unprecedented insight into how neighboring volcanoes can interact, with magma movements under one influencing activity at the other. The findings, based on extensive seismic and satellite data, highlight the dynamic and interconnected nature of the region's volcanic plumbing, which has significant implications for hazard assessment.
Key Takeaways
- A 2025 volcanic crisis showed that the Santorini and Kolumbo volcanoes, located 7 km apart, share a linked magma feeding system.
- The crisis began with gradual ground uplift at Santorini, followed by a major magma dike intrusion sourced from a reservoir under Kolumbo.
- This intrusion, approximately 13 km long, caused over 30,000 earthquakes and significant seafloor deformation.
- The study reveals a cascading sequence of events, showing how pressure changes in one part of the system can trigger large-scale magma movement in another.
A Sequence of Unrest
The volcanic activity unfolded in distinct phases, providing scientists with a clear timeline of events. The first signs of unrest appeared months before the main crisis. From July 2024 to January 2025, monitoring instruments detected a gradual uplift within the Santorini caldera.
Satellite data confirmed this inflation, showing the ground had risen by approximately 50 millimeters (about 2 inches). According to the study, this was caused by about 0.004 cubic kilometers of magma flowing into a shallow reservoir located roughly 3.8 kilometers beneath the caldera. This same reservoir was active during a similar period of unrest in 2011-2012.
The Main Event: An Intense Earthquake Swarm
The situation escalated dramatically on January 27, 2025. An intense swarm of earthquakes began abruptly between Santorini and Kolumbo, signaling a significant geological event was underway. This marked the start of a major magma intrusion.
A massive sheet of magma, known as a dike, began forcing its way through the Earth's crust. This dike originated from a mid-crustal magma reservoir located approximately 7.6 kilometers beneath the Kolumbo volcano. As the magma moved, it triggered intense seismic activity and caused rapid ground deformation.
By the Numbers: The 2025 Volcanic Crisis
- 30,000+ earthquakes recorded during the crisis.
- 13 km: The approximate length of the magma dike intrusion.
- 0.31 km³: The estimated volume of magma that filled the dike.
- 50 mm: Ground uplift measured at Santorini before the main crisis.
- 32 cm: Seafloor subsidence recorded at Kolumbo's crater.
Mapping the Magma's Path
By combining data from a wide array of instruments, researchers were able to track the magma's movement with remarkable precision. The high-resolution earthquake catalogue, generated using machine learning, showed the dike propagating northeastwards away from Santorini and towards the island of Anhydros.
The dike's journey was not smooth. It advanced in at least 12 distinct surges, with periods of intense seismicity and rapid propagation followed by quieter phases. During its most active phase, the dike traveled at speeds of about 1 kilometer per hour.
"This dynamic migration pattern, along with the substantial surface deformation observed... is characteristic of magmatic dike intrusions in extensional domains," the researchers noted in their paper published in Nature.
As the dike inflated with magma, the reservoir beneath Kolumbo deflated. This caused significant subsidence, with the seafloor at Kolumbo's crater dropping by as much as 32 centimeters (12.6 inches). The volume of magma that filled the dike was roughly four times greater than the volume lost from the Kolumbo reservoir, suggesting the intrusion was fed by a much deeper, more primitive magma source.
Santorini and Kolumbo: A Hazardous History
The Christiana-Santorini-Kolumbo volcanic field is one of the most active in the Aegean Sea. Santorini is famous for the Minoan eruption around 1600 BCE, one of the largest volcanic events in human history. The submarine Kolumbo volcano, though less known, produced a major explosive eruption in 1650 CE that generated a tsunami and caused fatalities on Santorini. Understanding their connection is crucial for regional safety.
A Coupled Volcanic System
The 2025 crisis provides the strongest evidence to date that the Santorini and Kolumbo volcanic systems are hydraulically connected deep underground. The sequence of events—inflation at Santorini followed by a dike intrusion sourced from Kolumbo—suggests that the two volcanoes may compete for the same deep magma supply.
Researchers theorize that the initial magma recharge beneath Santorini may have increased pressure within the broader plumbing system. This pressure change could have ultimately caused the reservoir beneath Kolumbo, which may have been closer to a failure point, to rupture and feed the massive dike intrusion.
"The cascading course of events during the crisis may indicate that both systems share and possibly compete for the same magma supply at depth," the study states. This type of interaction, where activity at one volcano triggers a response at another, has been observed in other volcanic regions like Hawaii and Iceland, but the 2025 Aegean event offers an exceptionally detailed look at the process.
Implications for Future Hazards
While the 2025 dike intrusion did not result in an eruption, it has reshaped the understanding of volcanic hazards in the region. The magma stalled 3 to 5 kilometers below the seafloor in an area where the water is only about 200 meters deep.
An eruption in such shallow water could be highly explosive due to the interaction of magma and seawater, a process known as a phreatomagmatic eruption. The study highlights the importance of the magma's final ascent path in determining the style and hazard potential of any future eruption.
The event also underscores the challenge of forecasting volcanic activity. Despite clear precursor signals like ground inflation and increased gas emissions at Santorini, the subsequent large-scale dike intrusion from Kolumbo would have been impossible to predict. The authors conclude that integrated, real-time monitoring of seismicity, ground deformation, and gas emissions is essential for improving hazard assessment and providing early warnings in this volcanically active region.