First of all, some introductory information about volcanism in the Aegean sea.The volcanoes of the Aegean volcanic arc occur both onshore at the areas of Methana,Poros, Milos, Santorini, Kos and Nisyros and offshore like: Pausanias in the western Saronikos GulfAntimilos Volcanic Fieldthe Kolumbo volcano and other small cones northeast of Santorini in the submarine area around Nisyros.Submarine volcanoes occupy a significant area in the active Hellenic Volcanic Arc either in the form of independent features or as an offshore continuation of the volcanic islands. The average basal depth of the volcanoes occurring in the south Aegean Sea is approximately 600 meters. The volcanic relief may reach up to 1200m creating steep cones or domes. The volcanic structure is hosted within extensional neotectonic basins/grabens crosscutting the Plio-Quaternary sedimentary sequences. The large marginal faults of the basins are usually normal faults sometimes associated to textural NE-SW strike-slip zones. The prevailing tectonic orientation is NE-SW in Santorini and Nisyros and NW-SE in Methana and Milos, following the general geometry of the volcanic arc. E-W faults are observed to disrupt the previous arc-parallel NW-SE structures in Methana and Milos.
And a few words about the submarine area of Santorini caldera.The maximum diameter of the caldera is nearly 11 km long in a north-south direction (longest axis), while the minimum east-west diameter is approximately 7 km long (short axis). The deepest point of the caldera bottom is 389 m below sea level, while the caldera walls are approximately 300 m altitude above sea level.The floor of 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 - 300 m in extent. The vents form hundreds of 1 to 4 meter diameter mounds, covered by a yellowish bacterial mat, that are up to 1 meter high. The temperature in these mounds is around 15 to 17° C or about 5° C above ambient temperature. The North Basin hydrothermal vent field is located in line with the normal fault system of the Kolumbo rift, and also near the margin of a shallow intrusion that occurs within the sediments of the North Basin. Similar vent mounds occur in the South Basin, where most of the low temperature vents are seeps traced along a ridge which separates the West and South Basins. Some more active vents also occur at the shallow depths of the submarine flanks of the Kameni volcanic islands. Here is a photo of Hercules collecting a push core of a yellow bacterial colony and sediment from the hydrothermal vent field in the northern basin of Santorini and a video, in which the ROV examines the seabed morphology at the same area.
ROV exploration of Santorini Caldera, Greece. Nomikou, P.
10ο Πανελλήνιο υμπόςιο Ωκεανογραφίασ & Αλιείασ 7-11 Μαϊου 2012, ΑθήναROV EXPLORATION OF SANTORINI CALDERA, GREECENomikou P.¹*, Croff Bell K.², Bejelou K.¹, Parks M.³, Antoniou V.¹ 1 National and Kapodistrian University of Athens, 15784 Zographou, Athens, Greece 2 Graduate School of Oceanography, University of Rhode Island, Narragansett Bay Campus, USA 3 University of Oxford, UK
(Nomikou et al., 2012 GLOPLACH) These three main volcanic centers and all the smaller volcanic cones northeast of Kolumbo, are aligned along the NE-SW trending Santorini-Kolumbo volcano-tectonic line
Καταδφσεις με το Βαθυσκάφος«ΘΕΤΙΣ» του ΕΛΚΕΘΕ (2005, 2007) SKAI www.explorenautilus.gr (2011)
Sigurdsson et al., 2006 Hydrothermal vents occur in both the North and South Basin of the caldera. They form a vent field in the NE part of the North Basin that is 200 by 300m in extent. The vents form hundreds of 1 to 4m diameter mounds of yellowish bacterial mat that are up to 1m high. Temperatures in the mound are around 15 to 17 C or about 5 C above ambient temperature. The North Basin hydrothermal vent field is located in line with the normal fault system of the Kolumbo rift, and also near the margin of a shallow intrusion that occurs within the sediments of the North Basin. Similar vent mounds occur in the South Basin, where most of the low temperature vents are seeps along a ridge separating the West and South Basins and on the submarine flanks of the Kameni volcanic islands.
Tectonic graben in line with Kolumbo line (NE-SW direction)
Swath Bathymetric Map of Kolumbo Volcano 500m depth The caldera rim lies at about 150 m depth forming a submarine circular cliff of 350 m. The crater walls display a scalloped morphology that is visible by undulating contour lines.The topographic difference is apparently created by the collapse of a relevant volcanic cone Nomikou et al., (2012-in review)
Οιυδροθερμικϋσ καμινϊδεσπαρουςιϊζουν υψηλό πορώδεσ, μεϋναν κεντρικό αγωγό που δομεύται απόςουλφύδια και θειώκϊ ϊλατακαι βοηθϊ τη ροό τωνρευςτών προσ τα ϋξω. Carey et al., 2011, Oceanography
Parks et al., 2012, Nature (in review)The source has an effective volume of 1−2×107m3 for the full year of 2011, and is centredslightly to the north of Nea Kameni at a depth Our soil gas surveys detected an apparent increase in CO2of 4-7 kilometres. emissions between July 2011 and September 2011. CO2 effluxes now exceed 12 kg m-2 day-1, with a total flux of 39 tonnes of CO2 per day (Parks et al, 2012)
Nomikou et al., 2011, Tectonophysics (in press)