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

Abstract

Abstract:The 1650 AD 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 1650 AD tsunami was found along the coast of Santorini Island at maximum altitudes ranging between 3.5 m a.s.l. (Perissa, southern coast) and 20 m a.s.l. (Monolithos, eastern coast), corresponding to a minimum inundation of 360 and 630 m respectively. Tsunami deposits consist of an irregular 5 to 30 cm thick layer of dark grey sand that overlies pumiceous deposits erupted during the Minoan eruption and are found at depths of 30-50 cm 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 1650 AD Kolumbo tsunami is a 250 m high water surface displacement generated by underwater explosion with an energy of ~2 × 10 16 J at water depths between 20 and 150 m. 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 (< 5 minutes) are needed. Pyroclastic flows cannot be discarded, but the required flux (10 6 to 10 7 m³.s -1 ) is exceptionally high compared to the magnitude of the eruption.

Evidence on the Koseda coast of Yakushima Island of a tsunami during the 7.3 ka Kikai caldera eruption

“…During the 7.3 ka Kikai eruption, phreatomagmatic explosions might have occurred. Comparison with tsunami from the 1,650 Kolumbo (Ulvrova et al, ) eruption indicates, however, that such explosions would have been unlikely to generate a tsunami large enough to explain far‐field deposition of Unit TG (Maeno & Imamura, ).…”

“…These researchers also simulated tsunamis caused by pyroclastic flows entering the sea and concluded that caldera collapse would have generated larger tsunamis than pyroclastic flows and that caldera collapse was the likely cause of tsunamis during the 7.3 ka eruption. The duration of sector collapse must, however, have been very short (perhaps unrealistically so) to generate large waves (Ulvrova et al, ).…”

Source mechanisms of volcanic tsunamis

“…For instance, the bulk volume of the 1991 caldera collapse at Pinatubo, Philippines, might have subsided in 34 min [121]. Ulvrová et al [15] demonstrated that caldera collapse of the Kolumbo submarine volcano, Aegean Sea, would produce significant wave heights (more than 1 m) on the shorelines of Santorini Island if the bulk subsidence lasted less than 10 min (figure 5). Furthermore, determining the source of tsunamis generated during shallow-water calderaforming eruptions is often problematic because different tsunamigenic processes might be involved: the caldera collapse itself, but also pyroclastic flows, underwater explosions, earthquakes, slope instabilities and shock waves.…”

Probabilistic Tsunami Hazard Analysis: Multiple Sources and Global Applications

“…Specific source mechanisms of volcanic tsunamis include underwater explosions, pyroclastic flows, lava, and lahars entering the water, slope failures, volcanic earthquakes, shock waves from large explosions, and caldera subsidence (Begét, ; Day, ; Latter, ; Kienle et al, ; Paris, ). Volcanic tsunamis are generally characterized by short‐period waves, greater dispersion, and limited far‐field effects compared to earthquake‐generated tsunamis, but the diversity of source mechanisms imply different types of waves (e.g., Choi et al, ; Le Méhauté & Wang, ; Nomanbhoy & Satake, ; Maeno & Imamura, ; Ulvrova, Paris, et al, ; Watts & Waythomas, ; Yokoyama, ). Owing to the diversity of complexity of these sources, inclusion of volcanic tsunamis into PTHA developed slowly.…”

“…Experimental and numerical simulations coupled with field data (observations, geology) progressively increased our knowledge of the physical processes and main parameters implied in volcanic tsunamis. Ulvrova, Paris, et al () demonstrated that the short duration (<10 minutes) required for a caldera subsidence to generate a tsunami is often unrealistic as caldera collapses typically last from few to several hours (e.g., Folch & Marti, ; Stix & Kobayashi, ). In the case of underwater eruptions, the expansion, rise, and gravitational collapse of the water crater produced by the explosion itself can produce tsunamis, depending on the water depth and energy of explosion (e.g., Le Méhauté & Wang, ).…”