Understanding Extreme Geohazards: The Science of the Disaster Risk Management Cycle European Science Foundation Conference November 28 to December 1, 2011, Sant Feliu de Guixols, Spain

Volcanic Hazard in the Kolumbo Submarine Volcanic Zone NE of Santorini Island

Paraskevi Nomikou (1), S. Carey (3), D. Papanikolaou (1), K. Croff Bell (3), D. Sakellariou (2), M. Alexandri (2), K. Bejelou (1)
(1) University of Athens, Department of Geology and Geoenvironment, Panepistimioupoli Zografou, 15784 Athens, Greece, evi@ath.hcmr.gr, dpapan@geol.uoa.gr, bejelouk@gmail.com
(2) Institute of Oceanography, Hellenic Centre for Marine Research, POBox 712, 19013 Anavyssos, Greece, sakell@ath.hcmr.gr, matina@ath.hcmr.gr
(3) Graduate School of Oceanography, University of Rhode Island, Narragansett, kcroff@gso.uri.edu, scarey@gso.uri.edu

Integrated evaluation of the swath bathymetry of the Anhydros basin (NE of Santorini Volcano) and seismic profiling data indicate that the linear distribution of the volcanic cones is controlled by strike-slip faults which run parallel to the long axis of the basin. This transtensional zone has provided pathways for subduction generated magmas to reach the surface and form at least 20 submarine volcanic centers that are aligned along two principal trends. The southwesterly portions of both trends intersect approximately within the crater of Kolumbo, the largest submarine center within the NE zone. Moving to the northeast the centers diminish significantly in size and are all equal to or less than 1.0 km3 in volume. The majority of the cones are dome-shaped and lack a recognizable summit crater suggesting that the dominant form of eruptive activity involved effusive dome building. However, the presence of some craters and the common occurrence of bedded volcaniclastic deposits indicates that at least part of the submarine activity was explosive. Their small size also suggests that the activity may have been monogenetic in many cases. New seismic tomography interpretations also suggests that an active magma chamber exists beneath Kolumbo at a depth of 5-6 km and that it may be linked to the nearby island of Santorini. Frequent seismic activity also continues northeast of Kolumbo along the rift basin. We note that current seismic activity is located more in line with easterly trend of the northeast cones, in contrast to the near lack of recent earthquakes along the more westerly trend. The higher level of seismicity in the eastern trend may be facilitating enhanced fluid migrations in the crust which are being manifest as low temperature hydrothermal venting and manganese precipitation on cones 61 and 68.

Our result suggest that hazards associated with the northeast cones are relatively low based on 1) lack of fresh outcrops of volcanic products, 2) dominant effusive dome-building style based on typical morphology, 3) very small volume of individual erupted products, and 4) relatively deep water depths at potential summit vents (majority >200 m). Apart from Kolumbo it appears that the cones aligned along the more easterly trend are perhaps undergoing more active volcanological/tectonic processes based on the distribution of seimicity and occurrence of hydrothermal venting. However, Kolumbo remains the most significant source of future volcanic hazards within this zone northest of Santorini and warrants a program of integrated monitoring.