The 'swarm' of tens of thousands of earthquakes near the Greek island of Santorini earlier this year was triggered by molten rock pumping through an underground channel over three months, scientists have discovered.
They used physics and artificial intelligence to work out exactly what caused the more than 25,000 earthquakes, which travelled about 20km (12 miles) horizontally through the Earth's crust.
They used each of the tremors as virtual sensors, then used artificial intelligence to analyze patterns associated with them.
One of the lead researchers, Dr. Stephen Hicks from UCL, said combining physics and machine learning in this way could help forecast volcanic eruptions.
What happened in Santorini?
The seismic activity stirred beneath the Greek islands of Santorini, Amorgos, and Anafi in January 2025. The islands experienced tens of thousands of earthquakes—many of which were over magnitude 5.0 and could be felt.
Many tourists fled, and locals feared that the nearby underwater volcano, Kolumbo, might erupt, or that this was a seismic prelude to a larger earthquake, like the 1956 magnitude 7.7 quake that struck the region.
The scientists created a 3D map of the Earth around Santorini and mapped the evolving patterns of seismic activity of each tremor and the movement and stress in the crust. This resulted in a detailed model of exactly what drove this months-long seismic swarm.
They determined that the event was driven by the horizontal movement of magma—from beneath Santorini and the Kolumbo volcano—through a 30km channel that is more than 10km beneath the seafloor between Santorini and Anydros.
Researchers estimated the volume of magma that moved could have filled 200,000 Olympic-sized swimming pools. These 'magma intrusions' smashed through layers of rock, triggering thousands of tremors.
Lead author Anthony Lomax explained, 'The tremors act as if we had instruments deep in the Earth, and they're telling us something. When we analyze the pattern those earthquakes make in our 3D model of the Earth, it matches very, very well what we expect for magma moving horizontally.'
Does this mean the Santorini unrest is over?
For now, it appears to be over. Dr. Hicks explained, 'The magma remained quite deep—more than 8km depth—in the crust. We know that magma can ascend and erupt at the surface quickly, but because the activity has now died down, we can be almost certain that the melt got stuck and cooled down deep in the crust.'
However, volcanoes can enter prolonged phases of unrest and unpredictability that can last many years, as seen in recent activity in south-west Iceland.
Using AI, combined with the fundamental physics of how the Earth's crust moves, could transform the ability to monitor and understand volcanic activity, helping keep people in seismically active areas safe. According to Dr. Hicks, 'Ultimately, this could be used as a forecasting tool. Whenever we see a cluster of earthquakes, that is data that can be used to work out the most likely cause.'
