Volcanic crises, driven by renewed magma inflow and migration, result in surface deformation and seismicity that can provide unique insights into the structure of volcanic systems and magmatic processes. Although the highly explosive volcanoes of Santorini and Kolumbo1,2 in the Greek Aegean Sea are just 7 km apart, their potentially coupled deep magmatic feeding systems are only poorly understood3,4. The 2025 volcano–tectonic crisis of Santorini simultaneously affected both volcanic centres, providing insights into a complex, multistorage feeder system. Here we integrate onshore and marine seismological data with geodetic measurements to reconstruct magma migration before and during the crisis. Gradual inflation in the Santorini caldera, beginning in mid-2024, preceded the January 2025 intrusion of a magma-filled dike sourced from a mid-crustal reservoir beneath Kolumbo, indicating a link between the two volcanoes. Joint inversion of ground and satellite-based deformation data indicates that approximately 0.31 km3 of magma intruded as an approximately 13-km-long dike, reactivating principal regional faults and arresting 3–5 km below the seafloor. The 2024–2025 resurgence of magmatic activity beneath both volcanic centres and their apparent coupling provides insights into the dynamic interplay of magma storage, transport and reservoir failure beneath neighbouring volcanoes.
