The island group of Santorini is the most well-known and active volcanic center 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.
