South Aegean Volcanic Arc in the context of "Bodrum"

Santorini, officially Thira or Thera, is a Greek island in the southern Aegean Sea, about 200 km (120 mi) southeast from the mainland. It is the largest island of a small, circular archipelago formed by the Santorini caldera. It is the southernmost member of the Cyclades group of islands, with an area of approximately 73 km (28 sq mi) and a 2021 census population of 15,480. The municipality of Santorini includes the inhabited islands of Santorini and Therasia, and the uninhabited islands of Nea Kameni, Palaia Kameni, Aspronisi, Anydros, and Christiana. The total land area is 91 km (35 sq mi). Santorini is part of the Thira regional unit.

Santorini is the most active volcanic centre in the South Aegean Volcanic Arc. The volcanic arc is approximately 500 km (300 mi) long and 20 to 40 km (12 to 25 mi) wide. The region first became volcanically active around 3–4 million years ago, though volcanism on Thera began around 2 million years ago with the extrusion of dacitic lavas from vents around Akrotiri. One of the largest volcanic eruptions in recorded history struck the island about 3,600 years ago, leaving a large water-filled caldera surrounded by deep volcanic ash deposits.

The volcanism of Italy is due chiefly to the presence, a short distance to the south, of the boundary between the Eurasian Plate and the African Plate. Italy is a volcanically active country, containing the only active volcanoes in mainland Europe (while volcanic islands are also present in Greece, in the volcanic arc of the southern Aegean). The lava erupted by Italy's volcanoes is thought to result from the subduction and melting of one plate below another.

Three main clusters of volcanism exist: a line of volcanic centres running northwest along the central part of the Italian mainland (see: Campanian volcanic arc); a cluster northeast of Sicily in the Aeolian Islands; and a cluster southwest of Sicily around the island of Pantelleria, in the Mediterranean's Strait of Sicily. Sardinia has had a totally separate geological history from that of the rest of Italy, where several cycles of volcanic activity occurred, the last of which ended at the beginning of the Pleistocene, but currently hosts only permanently extinct volcanoes.

The Hellenic Trench (HT) is an oceanic trough located in the forearc of the Hellenic arc, an arcuate archipelago on the southern margin of the Aegean Sea plate, or Aegean Plate, also called Aegea, the basement of the Aegean Sea. The HT begins in the Ionian Sea near the mouth of the Gulf of Corinth and curves to the south, following the margin of the Aegean Sea. It passes close to the south shore of Crete and ends near the island of Rhodes just offshore Anatolia.

In the classical theory of its origin the HT is an oceanic trench containing the Hellenic subduction zone, directly related to the subduction of the African plate under the Eurasian plate. Alternate views developed later on additional data question the classical view postulating that the HT may be the result wholly or partially of back-arc extension and slab rollback. The "partial" view hypothesizes that the western leg of the HT, Ionian Sea east to eastern Crete, exhibits the line of subduction and therefore is an oceanic trench. The "not at all" view, relying on the theory that the subduction line is under or south of the Mediterranean Ridge, questions whether any of the HT is currently subductional. If not, it is merely a legacy, a remnant of a previous subduction zone that has gone elsewhere.