Large volcanic eruptions, earthquakes, and tsunamis in Santorini: a multi-hazard physical laboratory of global interest

The Santorini volcano, Greece, attracts global scientific interest and constitutes a top tourist destination. The 17th century BCE eruption (“Minoan event") was likely the largest ever experienced by humanity. It was associated with significant tephra falls, earthquakes, and tsunamis inundating the eastern Mediterranean basin. Global climate changes were attributed to the Minoan event. Geological and archaeological evidence supports that the Minoan event drastically influenced eastern Mediterranean civilizations. Minoan tephra layers formed key horizon markers driving revisions of the Mediterranean civilization chronology. Comparative studies indicate great similarity between Santorini and Krakatoa, but the Minoan eruption exceeded in size the 1883 CE Krakatoa eruption. During historical times the volcanic cycle in Santorini restarted with eruptions of smaller size and magma emplacement in the caldera, thus shaping the Kamenae (Burned) islands, exactly as happened with the post-1883 generation of the Anak (Child) island in the Krakatoa caldera. In 1650 CE, a violent eruption occurred at the submarine Kolumbo volcano, which is situated a few kilometers outside the Santorini caldera but very likely is fed by the same magmatic chamber. Further research is needed to understand if magma generation at depth is possibly controlled by the occurrence of large-magnitude intermediate-depth earthquakes. The 1650 CE eruption and associated strong earthquakes and tsunamis caused loss of life and significant destruction. After several small-to-medium eruptive episodes during the 18th-20th centuries, Santorini has remained dormant since 1950. However, on 9 July 1956, the area to the east of Santorini was ruptured by a magnitude 7.7 tectonic earthquake, which, along with its large tsunami, caused extensive loss of life and destruction in the entire southern Aegean Sea. Submarine surveys indicate that the 1956 rupture zone possibly belongs to the same NE-SW-trending fracture zone passing from the Kolumbo and Santorini volcanoes. There is no historical evidence for similar tectonic earthquakes occurring in the past. Data-driven probabilistic seismic hazard assessment utilizing incomplete and uncertain earthquake catalogues indicates that the 1956-type earthquakes may have very long repeat times. During 2025, an unusual cluster comprising thousands of earthquakes but with a maximum magnitude of only 5.3 and sources at distances of 20-40 km to the east of Santorini caused extensive social anxiety. This was magnified because of two reasons. First, preventive measures taken by civil protection authorities were unprecedented. Second, uncontrolled public statements were expressed by specialists and non-specialists about imminent eruptions and forthcoming large earthquakes, which raised important geoethical challenges. The seismic crisis received international attention because Santorini is a spot of worldwide tourist interest. More than 13,000 people evacuated voluntarily. For the interpretation of the cluster, the “seismic swarm” hypothesis appears more as a “deus ex machina” explanation than a convincing scientific result. The competing “foreshocks-mainshock-aftershocks” model fits the data better. Santorini is a key volcano offering results valuable for better understanding the behavior of many volcanoes around the globe, revealing global climate impacts of volcanic origin, deciphering unknown aspects regarding prehistoric civilizations in the Mediterranean, and providing important lessons learned for volcanic and other geohazard management.