Source of the tsunami generated by the 1650 AD eruption of Kolumbo submarine volcano (Aegean Sea, Greece)

Abstract

The 1650AD explosive eruption of Kolumbo submarine volcano (Aegean Sea, Greece) generated a destructive tsunami. In this paper we propose a source mechanism of this poorly documented tsunami using both geological investigations and numerical simulations. Sedimentary evidence of the 1650AD tsunami was found along the coast of Santorini Island at maximum altitudes ranging between 3.5m a.s.l. (Perissa, southern coast) and 20m a.s.l. (Monolithos, eastern coast), corresponding to a minimum inundation of 360 and 630m respectively. Tsunami deposits consist of an irregular 5 to 30cm thick layer of dark grey sand that overlies pumiceous deposits erupted during the Minoan eruption and are found at depths of 30–50cm below the surface. Composition of the tsunami sand is similar to the composition of the present-day beach sand but differs from the pumiceous gravelly deposits on which it rests. The spatial distribution of the tsunami deposits was compared to available historical records and to the results of numerical simulations of tsunami inundation. Different source mechanisms were tested: earthquakes, underwater explosions, caldera collapse, and pyroclastic flows. The most probable source of the 1650AD Kolumbo tsunami is a 250m high water surface displacement generated by underwater explosion with an energy of ~2×1016J at water depths between 20 and 150m. The tsunamigenic explosion(s) occurred on September 29, 1650 during the transition between submarine and subaerial phases of the eruption. Caldera subsidence is not an efficient tsunami source mechanism as short (and probably unrealistic) collapse durations (<5min) are needed. Pyroclastic flows cannot be discarded, but the required flux (106 to 107m3·s−1) is exceptionally high compared to the magnitude of the eruption.