Submarine evidence of a debris avalanche deposit on the eastern slope of Santorini volcano, Greece

Abstract

Hummocky seafloor features were discovered on the eastern flank of Santorini volcano, Greece. Multibeam bathymetric mapping, airgun seismic profiling, side scan sonar survey, and remotely operated vehicle (ROV) dives have been carried out to characterize the nature of the hummocks. These hummocks appear to be composed of several tens of blocks that are up to several hundred meters in diameter, and are the surface expression of a much larger deposit than is observed in the bathymetry. The sidescan and airgun data show that the deposit covers an area of approximately 6km wide by 20km long, and is up to 75m thick. We estimate the total volume of the deposit to be approximately 4.4×109m3. Sampling of these blocks show they are composed of pyroclastic flow deposits produced during the Minoan eruption of Santorini (ca. 3600BP). We propose that the deposit is the result of a multi-stage landslide event that was caused by one of the several large earthquakes or volcanic eruptions that have occurred in the vicinity of Santorini since the Minoan eruption. One or more of these events likely triggered the destabilization of a part of the eastern flank of Santorini, which led to a debris avalanche, depositing blocks and forming a hummocky terrain at the base of the island's slope. The mass movement later evolved into a turbulent suspension flow that traveled 20km or more from the presumed initial failure. Given the size of the landslide deposit, it might have a tsunami potentially affecting the islands across the southern Aegean Sea. The understanding of earthquake–landslide dynamics has important implications for hazard assessment in this seismically active, historical, and highly populated region of the world.