Santorini (Greek: Σαντορίνη, pronounced [sandoˈrini]), classically Thera (English pronunciation /ˈθɪərə/), and officially Thira (Greek: Θήρα [ˈθira]), is an island in the southern Aegean Sea, about 200 km (120 mi) southeast of Greece’s mainland. It is 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 km2 (28 sq mi) and a 2011 census population of 15,550. The municipality of Santorini includes the inhabited islands of Santorini and Therasia and the uninhabited islands of Nea Kameni, Palaia Kameni, Aspronisi, and Christiana. The total land area is 90.623 km2 (34.990 sq mi). Santorini is part of the Thira regional unit.
Santorini is essentially what remains after an enormous volcanic eruption that destroyed the earliest settlements on a formerly single island, and created the current geological caldera. A giant central, rectangular lagoon, which measures about 12 by 7 km (7.5 by 4.3 mi), is surrounded by 300 m (980 ft) high, steep cliffs on three sides. The main island slopes downward to the Aegean Sea. On the fourth side, the lagoon is separated from the sea by another much smaller island called Therasia; the lagoon is connected to the sea in two places, in the northwest and southwest. The depth of the caldera, at 400m, makes it impossible for any but the largest ships to anchor anywhere in the protected bay; there is also a fisherman’s harbour at Vlychada, on the southwestern coast. The island’s principal port is Athinios. The capital, Fira, clings to the top of the cliff looking down on the lagoon. The volcanic rocks present from the prior eruptions feature olivine, and have a small presence of hornblende.
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 the Akrotiri.
The island is the site of one of the largest volcanic eruptions in recorded history: the Minoan eruption (sometimes called the Thera eruption), which occurred some 3,600 years ago at the height of the Minoan civilization. The eruption left a large caldera surrounded by volcanic ash deposits hundreds of metres deep and may have led indirectly to the collapse of the Minoan civilization on the island of Crete, 110 km (68 mi) to the south, through a gigantic tsunami. Another popular theory holds that the Thera eruption is the source of the legend of Atlantis.
Santorini was named by the Latin Empire in the thirteenth century, and is a reference to Saint Irene, from the name of the old cathedral in the village of Perissa – the name Santorini is a contraction of the name Santa Irini. Before then, it was known as Kallístē (Καλλίστη, “the most beautiful one”), Strongýlē (Greek: Στρογγύλη, “the circular one”), or Thēra. The name Thera was revived in the nineteenth century as the official name of the island and its main city, but the colloquial name Santorini is still in popular use. During the Ottoman Empire’s domination of the Aegean Sea, the Turkish exonym for the island was “Santurin” or “Santoron”.
The present municipality of Thera (officially: “Thira”, Greek: Δήμος Θήρας), which covers all settlements on the islands of Santorini and Therasia, was formed at the 2011 local government reform, by the merger of the former Oia and Thera municipalities.
Oia is now called a Κοινότητα (community), within the municipality of Thera, and it consists of the local subdivisions (Greek: τοπικό διαμέρισμα) of Therasia and Oia.
The municipality of Thera includes an additional 12 local subdivisions on Santorini island: Akrotiri, Emporio, Episkopis Gonia, Exo Gonia, Imerovigli, Karterados, Megalohori, Mesaria, Pyrgos Kallistis, Thera (the seat of the municipality), Vothon, and Vourvoulos.
Santorini’s primary industry is tourism. The two main sources of wealth in Santorini are agriculture and tourism. In recent years, Santorini has been voted one of the world’s most beautiful islands (2015 Travelers” Choice Awards Reader’s Choice Awards, amongst others).
Santorini remains the home of a small, but flourishing wine industry, based on the indigenous Assyrtyko grape variety. White varieties also include Athiri and Aidani, whereas red varieties include mavrotragano and mandilaria.
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 the Profitis Ilias Mountains, 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.
Volcanism on Santorini is due to the Hellenic Trench subduction zone southwest of Crete. The oceanic crust of the northern margin of the African Plate is being subducted under Greece and the Aegean Sea, which is thinned continental crust. The subduction compels the formation of the Hellenic arc, which includes Santorini and other volcanic centres, such as Methana, Milos, and Kos.
The island is the result of repeated sequences of shield volcano construction followed by caldera collapse. The inner coast around the caldera is a sheer precipice of more than 300 metres (980 ft) drop at its highest, and exhibits the various layers of solidified lava on top of each other, and the main towns perched on the crest. The ground then slopes outwards and downwards towards the outer perimeter, and the outer beaches are smooth and shallow. Beach sand colour depends on which geological layer is exposed; there are beaches with sand or pebbles made of solidified lava of various colours: such as the Red Beach, the Black Beach and the White Beach. The water at the darker coloured beaches is significantly warmer because the lava acts as a heat absorber.
The area of Santorini incorporates a group of islands created by volcanoes, spanning across Thera, Thirasia, Aspronisi, Palea, and Nea Kameni.
Santorini has erupted many times, with varying degrees of explosivity. There have been at least twelve large explosive eruptions, of which at least four were caldera-forming. The most famous eruption is the Minoan eruption, detailed below. Eruptive products range from basalt all the way to rhyolite, and the rhyolitic products are associated with the most explosive eruptions.
The earliest eruptions, many of which were submarine, were on the Akrotiri Peninsula, and active between 650,000 and 550,000 years ago. These are geochemically distinct from the later volcanism, as they contain amphiboles.
Over the past 360,000 years there have been two major cycles, each culminating with two caldera-forming eruptions. The cycles end when the magma evolves to a rhyolitic composition, causing the most explosive eruptions. In between the caldera-forming eruptions are a series of sub-cycles. Lava flows and small explosive eruptions build up cones, which are thought to impede the flow of magma to the surface. This allows the formation of large magma chambers, in which the magma can evolve to more silicic compositions. Once this happens, a large explosive eruption destroys the cone. The Kameni islands in the centre of the lagoon are the most recent example of a cone built by this volcano, with much of them hidden beneath the water.
The devastating volcanic eruption of Thera has become the most famous single event in the Aegean before the fall of Troy. It may have been one of the largest volcanic eruptions on Earth in the last few thousand years, with an estimated VEI (volcanic explosivity index) of 6 according to the last studies published in 2006, confirming the prior values. The violent eruption was centred on a small island just north of the existing island of Nea Kameni in the centre of the caldera; the caldera itself was formed several hundred thousand years ago by the collapse of the centre of a circular island, caused by the emptying of the magma chamber during an eruption. It has been filled several times by ignimbrite since then, and the process repeated itself, most recently 21,000 years ago. The northern part of the caldera was refilled by the volcano, then collapsing once more during the Minoan eruption. Before the Minoan eruption, the caldera formed a nearly continuous ring with the only entrance between the tiny island of Aspronisi and Thera; the eruption destroyed the sections of the ring between Aspronisi and Therasia, and between Therasia and Thera, creating two new channels.
On Santorini, a deposit of white tephra thrown from the eruption is found lying up to 60 m (200 ft) thick, overlying the soil marking the ground level before the eruption, and forming a layer divided into three fairly distinct bands indicating different phases of the eruption. Archaeological discoveries in 2006 by a team of international scientists revealed that the Santorini event was much more massive than previously thought; it expelled 61 cubic kilometres (15 cu mi) of magma and rock into the Earth’s atmosphere, compared to previous estimates of only 39 cubic kilometres (9.4 cu mi) in 1991, producing an estimated 100 cubic kilometres (24 cu mi) of tephra. Only the Mount Tambora volcanic eruption of 1815, the 181 AD eruption of Lake Taupo, and possibly Baekdu Mountain’s 969 AD eruption have released more material into the atmosphere during the past 5,000 years.