Santorini, the most spectacular island in the Aegean Sea owes its exceptional landscape to the Minoan eruption in the 17th century BC and the formation of the famous caldera in the middle of the island. The caldera walls rise to over 300m above sea level while maximum depth of the caldera seafloor is about 390m. The Minoan eruption is considered the second largest eruption in historical times, after the Tambora volcano eruption in Indonesia in 1815. The oldest volcanic products of Santorini are 1.5-1.6 million years old. Several eruptive cycles are distinguishable on the island with the Minoan eruption being the most recent. Minoan ash forms a white colored cap over the island up to 50m thick. Beneath that cap are successive multicolored lava layers, pyroclastic flows, ash deposits and other volcanic formations exposed on the upright caldera walls, providing witness to the diverse volcanic history of the island. Since the devastating Minoan eruption in the 17th century BC, many significantly weaker activity phases have occurred, and the landscape has continued to change even during very recent years. The Nea Kameni island in the centre of the caldera forms the summit of the actively growing new volcanic center. The ancient geographer Strabo was the first to record volcanic eruptions inside the Santorini caldera. He described the birth of a newly formed small island in 197 BC in the middle of caldera which now forms the Palea Kameni. Several eruptive phases followed the birth of Kameni islands (Palaea and Nea) in the years 46-47, 726, 1570-1573, 1707-1711, 1866-1870, 1925-1928, 1938-1941 and 1950 AD as the most recent eruption.The floor of the Santorini caldera was explored with ROV Hercules. A large number of hydrothermal vents were discovered, but in contrast to the high-temperature venting found in Kolumbo submarine volcano, only relatively low-temperature venting was observed within the Santorini caldera. They form a vent field in the NE part of the North Basin that is 200 by 300 m in extent. The vents form hundreds of 1 to 4 meter diameter mounds of yellowish bacterial mat that are up to 1 meter high. Temperatures in the mound are around 15 to 17° C or about 5° C above ambient temperature.The present configuration of the caldera consists of three distinct basins that form separate depositional environments, divided by the Kameni volcanic islands. The Northern Basin is the largest and deeper (389 m) developed between the Kamenes, Therasia and the northern part of the Santorini caldera. The Western Basin is the smaller and lies alongside the Aspronisi islet, Palaea Kameni and Southern Therasia with a medium depth (325 m). The South Basin is developed between the Kamenes and the southern part of the Santorini caldera covering a medium area with the shallowest sea bottom (297 m).
Figure: Swath bathymetric map of Santorini caldera using 10m isobaths, where the three post-Minoan caldera subbasins are indicated (the dotted borders show the basinal parts). Underwater photos taken by ROV “Hercules” show the low temperature hydrothermal field at the northern part of the caldera (a and b), the lava outcrop south of Nea Kammeni (c) and the lavas in the form of dikes south of Palaea Kameni (d).
(Nomikou P., Papanikolaou D., Alexandri M., Sakellariou D.: Submarine volcanoes along the Aegean Volcanic Arc. Special Issue of Tectonophysics: «The Aegean: a natural laboratory for tectonics» 2011 (in \review).http://www.nautiluslive.org/blog/2011/09/07/nea-kameni-and-palea-kameni
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