On the origin of submarine sediment features in the southern Aegean Sea

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Dissertations and Master's Theses (Campus Access), Page: 1-146

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Bell, Katherine Lynn Croff
Marine Geology
thesis / dissertation description
Geophysical mapping of the submarine region in the southern Aegean Sea, Greece, have revealed three regions with previously unstudied sediment features. This dissertation investigates these features, with the goal of identifying the processes by which they were deposited. The first region is the southwest flanks of Santorini volcano, where undulating or step-like features were discovered in 2006. Similar seabed features have been described in other submarine environments, but the interpretation of their origin as either deformational or depositional remains controversial. Features found on the slopes of Santorini are most similar to those found on other large subduction zone submarine calderas suggesting a common origin. We hypothesize that the features owe their origin to simultaneous catastrophic influx of unconsolidated volcaniclastic sediment and intense seismic activity associated with large-volume eruptions in subduction zone environments. The second region is the eastern flank of Santorini, where hummocky seafloor features were documented. Multibeam bathymetric mapping, airgun seismic profiling, side scan sonar survey, and remotely operated vehicle dives have been carried out to characterize the nature of the hummocks. Integration of geophysical data shows that the deposit covers an area of approximately 120 km2, and is up to 75 m thick; total volume of the deposit is approximately 4.4 km3. We propose that the deposit is the result of a multi-stage landslide event that was caused by an earthquake or volcanic eruption that occurred in the vicinity of Santorini. Finally, geophysical and ROV survey of the western Sea of Crete revealed significant sediment mass wasting on the slopes of Aphrodite Rise, the southwest Aegean Rise and the continental slope of Milos Basin. Results show that the region is stable under gravity loading for slope angles less than 30°; under earthquake loading, the region is extremely unstable. We investigate the effects of historical seismicity, and find that eleven earthquakes that occurred in the western Sea of Crete from 1604 to 2002 could have had particularly significant impacts on the seafloor. Understanding of earthquake-landslide dynamics in the southern Aegean Sea has important implications for hazard assessment in this seismically active, highly-populated region of the world. ^