The island group of Santorini is the most well-known and active volcanic centre of the Hellenic Volcanic Arc in the south Aegean Sea. It is a very complex stratovolcano dominated by a large, sea-flooded caldera created by several large explosive eruptions. The different products of about 2 million years of volcanic activity have accumulated around a small non-volcanic basement, that once formed a small island similar to the other cycladic islands. Most of the volcanic layers are visible in the multi-colored sequences of the impressive steep inner walls of the caldera, striking the visitor who reaches the island by boat.The last eruption took place in an phreatic eruption on Nea Kameni island in 1950.
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