Santorini officially Thira and classic Greek Thera, is an island in the southern Aegean Sea, about 200 km (120 mi) southeast from the Greek mainland. It's the largest island of a small, circular archipelago, which bears the same name and is the remnant of a volcanic caldera. It forms the southernmost member of the Cyclades group of islands, with an area of approximately 73 square kilometres (28 sq mi) and a 2011 census population of 15,550. The municipality of Santorini includes the inhabited islands of Santorini and Therasia, as well as the uninhabited islands of Nea Kameni, Palaia Kameni, Aspronisi and Christiana. The total land area is 90.623 square kilometres (34.990 sq mi). Santorini is part of the Thira regional unit.
It is the most active volcanic centre in the South Aegean Volcanic Arc, though what remains today is chiefly a water-filled caldera. The volcanic arc is approximately 500 km (310 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.
The expansion of tourism in recent years has resulted in the growth of the economy and population. Santorini was ranked the world's top island by many magazines and travel sites, including the Travel+Leisure Magazine, the BBC, as well as the US News. An estimated 2 million tourists visit annually.
The island's pumice quarries have been closed since 1986, in order to preserve the caldera. In 2007, the cruise ship MS Sea Diamond ran aground and sank inside the caldera. As of 2019, Santorini is a particular draw for Asian couples who come to Santorini to have pre-wedding photos taken against the backdrop of the island's landscape.
The Cyclades are part of a metamorphic complex that is known as the Cycladic Massif. The complex formed during the Miocene and was folded and metamorphosed during the Alpine orogeny around 60 million years ago. Thera is built upon a small, non-volcanic basement that represents the former non-volcanic island, which was approximately 9 by 6 km (5.6 by 3.7 mi). The basement rock is primarily composed of metamorphosed limestone and schist, which date from the Alpine Orogeny. These non-volcanic rocks are exposed at Mikro Profititis Ilias, Mesa Vouno, the Gavrillos ridge, Pyrgos, Monolithos, and the inner side of the caldera wall between Cape Plaka and Athinios.
The metamorphic grade is a blueschist facies, which results from tectonic deformation by the subduction of the African Plate beneath the Eurasian Plate. Subduction occurred between the Oligocene and the Miocene, and the metamorphic grade represents the southernmost extent of the Cycladic blueschist belt.
