Query: Therasia is in the volcanic island group of Visayas.

Relevant passages:
Santorini <=SEP=> Santorini ( Σαντορίνη , pronounced -LSB- sandoˈrini -RSB- ) , classically Thera ( English pronunciation -LSB- ˈθɪərə -RSB- ) , and officially Thira ( Greek : Θήρα -LSB- ˈθira -RSB- ) , is an island in the southern Aegean Sea , about 200 km 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 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 . 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 , is surrounded by 300 m 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 long and 20 to 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 to the south , through a gigantic tsunami . Another popular theory holds that the Thera eruption is the source of the legend of Atlantis .

Therasia <=SEP=> Therasia , also known as Thirasía , 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 km ² and its population was 319 inhabitants at the 2011 census . It is part of the municipal unit of Oia .   Thera and Therasia were separated by the Thera eruption .   At Knossos , in a LMIIIA context ( 14th century BC ) , seven Linear B texts while calling upon `` all the gods '' make sure to grant primacy to an elsewhere-unattested entity called qe-ra-si-ja and , once , qe-ra-si-jo . However this probably refers to a god or a person rather than to an island * Qherasia > Therasia .   Thirasia is also the book of Greek poet Dimitris Varos that became a music album and theatrical performance by Greek composer Giannis Markopoulos under the title Daring Communication - Electric Theseus .