Santorini caldera in the context of "Palaia Kameni"

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.

Therasia, also known as Thirasía (Greek: Θηρασία), is an island in the volcanic island group of Santorini in the Greek Cyclades. It lies north-west of Nea Kameni, a small island formed in recent centuries by volcanic activity and thus marking the centre of the island group. Therasia is the second largest island of the group, the largest by far being Thera.

Therasia has a land area of 9.299 square kilometres (3.590 sq mi) and its population was 249 inhabitants at the 2021 census. It is part of the municipal unit of Oia (Δημοτική Ενότητα Οίας).

Nea Kameni is a small, uninhabited Greek island of volcanic origin located in the Aegean Sea, within the flooded Santorini caldera. Nea Kameni (new burnt) and the neighbouring small island Palea Kameni (old burnt) have formed over the past two millennia through repeated eruptions of dacite lava and ash. The Roman historian Cassius Dio records in the year 47 CE "This year a small islet, hitherto unknown, made an appearance close to the island of Thera." Cassius' report may refer to Palaia Kameni. Pliny the Elder reported the emergence of a new island on July 8, in the year of the consulship of M. Junius Silanus and L. Balbus, thus 19 CE.

Major eruptions over the past 300 years took place in 1707–1712, 1866–1870, 1925–1928, and 1939–1941. The last small eruption happened in 1950 and involved lava dome extrusion.

Aspronisi (Greek: Ασπρονήσι) is an uninhabited island lying within the Santorini caldera. The island was originally formed by the massive Minoan eruption in the 2nd millennium BC, after which it was gradually built up by successive volcanic activity. The name Aspronisi, which means 'White Island' in Greek, is derived from the island being partially composed of white pumice.

Akrotiri (Greek: Ακρωτήρι) is a village and a community on the island of Santorini in Greece. It is located 15 kilometers south of the capital Fira, built on the slopes of a hill offering staggering views of the caldera cliffs. On top of this hill, there are remains of a Venetian castle (Goulas). Akrotiri is part of the Thira region and had 515 permanent inhabitants according to the Greek census of 2021.

Approximately 2 km southeast, the Minoan Bronze Age Akrotiri archaeological site is located. This is one of the most important of its kind in the Aegean.