The basement rock is primarily composed of metamorphosed limestone and schist, which date from the Alpine Orogeny.These non-volcanic rocks are exposed at Mikro Profititis Ilias, Mesa Vouno, the Gavrillos ridge, Pyrgos, Monolithos, and the inner side of the caldera wall between Cape Plaka and Athinios.
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).
), 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.
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 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.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 water at the darker coloured beaches is significantly warmer because the lava acts as a heat absorber.