The volcanic complex of Santorini is the most active part of the South Aegean Volcanic Arc, which includes the volcanoes of Methana, Milos, Santorini and Nisyros. It marks the subduction of the African tectonic plate underneath the Aegean subplate of the Eurasian tectonic plate, at a rate of up to 5 cm per year in a northeasterly direction. It is characterized by earthquakes at depths of 150–170 km.
The huge Minoan eruption of Santorini in the 17th century BC may have inspired the legend of Atlantis. It was rated 7, the highest score for a historical eruption, in the Smithsonian Global Volcanism Program's Volcanic Explosivity Index. source : WIKIPEDIA