Santorini (Greek: Σαντορίνη, pronounced [sadoˈrini]), classically Thera (English pronunciation /ˈθɪrə/), 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 comprises 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 possible for all but the largest ships to anchor anywhere in the protected bay; there is also a newly built marina at Vlychada, on the southwestern coast. The island's principal port is Athinias. 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 3600 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.
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 m 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 geologic layer is exposed; there are beaches with sand or pebbles made of solidified lava of various colours: the Red Beach, the Black Beach, the White Beach, etc. The water at the darker coloured beaches is significantly warmer because the lava acts as a heat absorber. Santorini has a group of islands. Those islands are named, Thera, Thirasia, Aspronisi, Palea, and Nea Kameni. They were are created by volcanoes and are located in the Aegean Sea just north of Crete.
In 1956 a major earthquake near Amorgos island resulted in the demolishing of many buildings in the north of Santorini, leading to the desertion of many of its villages. The expansion of tourism has resulted in the growth of the economy and population. The major settlements include Fira (Phira), Oia, Emporio, Kamari, Perissa, Imerovigli, Pyrgos, and Therasia. Akrotiri is a major archaeological site, with ruins from the Minoan era. Santorini's primary industry is tourism, particularly in the summer months. In 2007, the cruise ship MS Sea Diamond ran aground and sank inside the caldera. The island's pumice quarries have been closed since 1986, in order to preserve the caldera. Santorini was ranked world's top island for many other magazines and travel sites, including the Travel+Leisure Magazine, the BBC, as well as the US News.