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Santorini, named by early Venetians in honor of Saint Irene, forms a circular group of islands belonging to the Cyclades island chain in the southern Aegean Sea, located midway between mainland Greece to the west, Turkey to the east, and the island of Crete to the south The Cyclades form part of the Aegean island arc system, generated by northward subduction of the African plate along the arcuate Hellenic trench system located south of Crete Within this plate-tectonic setting, the ring-shaped group of islands known as Santorini includes Thera (the largest), Therasia (little Thera), Aspronisi, and the central Kameni Islands

The geologic record at Santorini reveals a long history of volcanic activity, consistent with its subduction-zone setting The archeological record indicates that Santorini has been inhabited by numerous civilizations going back to the 13th century BC, contemporaneous with the most recent eruptive events Historic eruptions may well have provided dramatic events, if not catastropic hazards, to these various civilizations Archeological excavations near the city of Akrotiri in southern Thera have revealed Bronze Age ruins of a particularly large and vibrant city, with well-preserved frescos and paintings, together with numerous artifacts The artifacts indicate that the island of Thera was colonized by the Minoans, a Bronze Age civilization named after the legendary King Minos of Crete Thera appears to have had a thriving Minoan economy provided by intensive trade througout the eastern Mediterranean Today, the remains of this flourishing community lie buried under a thick blanket of pumice generated by a massive Late Bronze Age eruption The exact date of the eruption remains somewhat controversial, although most radiometric studies show that it falls between 1615-1645 BC, consistent with a pronounced acid-ice layer from the Greenland cores, dated at 1636 BC

The islands of Santorini did not form from a single event, but rather from a variety of eruptions over a long period of time Geologic studies indicate that at least 12 eruptive phases have occurred over the last one million years The late Bronze Age event was a Plinian eruption of epic proportions, with an estimated Volcanic Explosivity Index (VEI) of 69 The immensity of this eruption is equaled or surpassed by only seven other terrestrial eruptions in the past four millennia Before this catastrophe, Santorini was a large circular island with a water-filled embayment to the south or southwest During the late Bronze Age eruption, the central highland of the volcanic island collapsed to generate the modern caldera The subaerial remnants of which form the three-island archipelago of Thera, Therasia, and Aspronisi

Caldera wall collapse was associated with intense seismic activity, voluminous pyroclastic airfalls, pyroclastic flows, and tsunamis, which damaged or destroyed the local Minoan civilization and the Minoan cities on adjacent islands The cataclysmic event was probably very similar in character to the 1883 eruption of Krakatau, which is also generated a submarine caldera associated with enormous tsunami and devastingly extensive pyroclastic flows The widepsread character of Santorini eruption is demonstrated by the broad distribution of Late Bronze Age tephra, found in both deep-sea sediments of the Aegean, Mediterranean, and Black Seas, and in archeological sites throughout the eastern Mediterranean coast

Although the ~1630 BC eruption of Santorini is recognized as one of the most explosive volcanic eruptions in historic times, the event is only a single eruption in a continuum of eruptive activity associated with subduction The geologic record over the past one million years indicates that less explosive Strombolian and Vulcanian eruptions have occurred at Santorini about once every 5000 years, and that Plinian-type events have occurred about once every 20,000 years Since the late Bronze Age eruption, the two Kameni islands, Nea and Palea Kameni, have formed in the center of the caldera by numerous eruptive events over the past 2000 years

There is little evidence that Santorini is in a permanent state of slumber The island group exhibits ongoing seismic activity, and both fumaroles and hydrothermal springs are common features on the islands It seems clear that we can expect another eruption The historic record would suggest that it will be a small-to-moderate eruption typical of those over the last 2000 years Volcanoes like Santorini, however, are inherently unpredictable, and we cannot rule out the possibility of another catastrophic eruption reminiscent of ~1630 BC