Santorini is a small, circular archipelago of volcanic islands located in the southern Aegean Sea, about 200 km south-east from Greece’s mainland. It is also known as Thera, forming the southernmost member of the Cyclades group of islands, with an area of approximately 73 km² (28 mi²) and a 2001 census population of 13,670. It is comprised of the Municipality of Thíra (pop. 12,440) and the Community of Oía (???, pop. 1,230, which includes 268 inhabitants resident on the offshore island of Therasia, lying to the west). They have a total land area of 90.623 km², which also includes the uninhabited islands of Nea Kameni, Palaia Kameni, Aspronisi, and Christiani (all part of the Municipality of Thira).
Santorini is essentially what remains of an enormous volcanic explosion, destroying the earliest settlements on what was formerly a single island, and leading to the creation of the current geological caldera. Its spectacular physical beauty, along with a dynamic nightlife, have made the island one of Europe’s tourist hot spots.
A giant central lagoon, more or less rectangular, and measuring about 12 km by 7 km (8 mi by 4 mi), is surrounded by 300 m (984 ft) high steep cliffs on three sides. The island slopes downward from the cliffs to the surrounding Aegean Sea. On the fourth side, the lagoon is separated from the sea by another much smaller island called Therasia; the lagoon merges with the sea in two places, in the northwest and southwest. The water in the centre of the lagoon is nearly 400 m (1300 ft) deep, thus making it a safe harbour for all kinds of shipping. The island’s harbours all lie in the lagoon and there are no ports on the outer perimeter of the island; 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 notably 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 name Santorini was given it by the Latin empire in the thirteenth century, and is a reference to Saint Irene. Before then it was named Kallist? (”the most beautiful one”), Strongyl? (”the circular one”), or Thera.
The island is the site of one of the largest volcanic eruptions the planet has ever seen: 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 feet deep and may have led indirectly to the collapse of the Minoan civilization on the island of Crete, 110 km (70 miles) to the south, through the creation of a gigantic tsunami. Another popular theory holds that the Thera eruption is the source of the legend of Atlantis (see below for detail).
The devastating volcanic eruption of Thera has become the most famous single event in the Aegean before the fall of Troy. The eruption would have been likely to have caused a significant climate upset for the eastern Mediterranean region; this may have been one of the biggest volcanic eruptions on Earth in the last few thousand years.
The violent eruption was centered 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 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 and then collapsed again 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, there is to be found a deposit of white tephra thrown from the eruption, lying up to 60 metres 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. New archaeological discoveries by a team of international scientists, in 2006, have revealed that the Santorini event was much more massive than previously thought; it expelled 61 km³ of magma and rock into Earth’s atmosphere, compared to previous estimates of only 39 cubic kilometres in 1991. Only the Mount Tambora volcanic eruption of 1815 (and possibly the eruption at Lake Taupo of 181 AD) released more material into the atmosphere during the past 5,000 years—at an estimated 100 cubic kilometres.