Plattform Platform	Reise-Nr. Cruise-No.	Zeitraum Period	Projekt Project	Arbeitsgebiet Working area
Poseidon	POS338	02.06.2006 - 13.06.2006		Mediterranean Sea Aegean Sea

Fahrtleiter Chief Scientist	Institut Institute	Auslaufhafen Port of departure	Einlaufhafen Port of return	Stationskarte Station map	Schiffsroute Trackchart
Hubscher Christian	Institut fur Geophysik der Universitat Hamburg	Piraeus	Piraeus

Ziel der Reise / Objectives of Cruise:

Active tectonic processes along the African-Eurasian collision zone are associated with catastrophic events including earthquakes, major volcanic eruptions, and tsunamis. Understanding how these processes can affect the eastern Mediterranean is of increasing scientific and public interest. The region includes a frequently crossed international sea traffic corridor and dense population centers. Furthermore, most of the small volcanic islands in the Aegean are major tourist attractions that contribute significantly to the wealth of this region. One of these Aegean islands is Santorini, which is a major explosive volcano and possibly one of the most dangerous volcanoes in Europe. During the past 150 million years, Santorini has had 12 major eruptions, and several of them ejected large columns of ash and debris high into the atmosphere. It is widely believed that the eruption of Santorini about 3600 years before present (B.P.) destroyed the Minoan civilization of Crete. In addition to the volcanic island, there are several submarine volcanic seamounts in the Aegean Sea. One of them, the Coloumbo seamount, is about eight kilometers northeast of Santorini, and recently has attracted attention due to the high earthquake activity of the Hellenic subduction zone. This activity is concentrated in an area northeast of Santorini, within the so-called Santorini-Amorgos zone. According to previous findings, the Santorini-Amorgos zone (SAZ) marks a major structural boundary in a dextral transtensional regime that subdivides the Hellenic volcanic arc into a seismically and volcanically quiet western and an active eastern part. The highest earthquake activity has been observed beneath the submarine Coloumbo volcano and northeast of it along the Santorini-Amorgos Ridge, which terminates south of the island of Amorgos. The activity close to the Coloumbo seamount is considered to be linked directly to a magma reservoir and to be influenced by the migration of magma and fluids toward the surface. Earthquakes northeast of the volcano also may result from magma and associated fluid migration toward the surface, according to some suggestions. The Santorini-Coloumbo volcanic complex includes one caldera at Santorini and one crater at Coloumbo. The caldera of Santorini is formed by four deep basins (from 290 to 390 meters deep). The Coloumbo volcano has a well-defined crater with a single basin (depth 500 meters). Until now, only a single underwater eruption has been reported for the Coloumbo volcano in 1650 A.D. The general scientific objectives of the first phase of the "Inspecting Coloumbo" project included the investigation of shallow expressions of deep-rooted tectonic or magmatic intrusions, which may result in active faulting or fluid migration, respectively. During the research cruise, the Santorini-Coloumbo complex as well as the SAZ were mapped in detail by means of multichannel seismic reflection and magnetic (1500 kilometers each) and gravity (2500 kilometers) profiling. For the active seismics, a bubble free airgun with about 100-hertz main frequency served as the seismic source. In the sediment basins, the signal penetrated to a depth of more than one kilometer beneath the seafloor. Data were received by two seismic sensor cables (streamers) of 600- and 150-meter length, respectively. The seismic data will help with (1) the reconstruction of Pliocene-Pleistocene tectonics; (2) the budgeting of pyroclastic deposits around Santorini and the Coloumbo volcano as well as in the SAZ; (3) the interpretation of individual eruption events of the Coloumbo and Santorini volcanoes; and (4) the detection of fluid migration paths and reservoirs associated with magmatic intrusions. The gravity and magnetic data will help to correlate shallow tectonic signals with deeper magmatic intrusions, and therefore determine the distinction between main faults above an intrusion or side branches.

Messungen / Measurements