Scenario-based tsunami hazard assessment at Kolumbo submarine volcano

Volcanic-induced tsunamis have a potentially devastating impact, especially in densely populated and/or touristic coastal areas. Kolumbo submarine volcano (Greece) experienced in 1650 CE an explosive eruption with eyewitnesses’ accounts of major tsunamis along the coasts of Santorini (Thera) and other islands. We present a scenario-based tsunami hazard assessment at this volcano based on existing simulations from literature and new simulations of tsunamis triggered by a less investigated but important mechanism, i.e., submarine landslides on the volcano flanks or within its crater. Simulation results show that the remobilization of a landslide volume of 150–300 Mm ³ inside the crater can produce tsunami waves larger than 10 m high along the NE coast of Thera and of the order of 5 m along the E and SE coasts. The expected tsunami arrival time ranges from 2 to 3 min along the NE coast of Thera up to 8–10 min on its SE coast. Such scenarios produce inundation areas consistent with those reconstructed for the 1650 CE event and tsunami waves propagating inland at velocities from 2 to 12 m/s. Simulation results also suggest that, given the landslide parameters assumed, it is unlikely that such a large volume landslide would mobilize from the SW-facing Kolumbo crater slopes given the relatively gentle topo-bathymetry of this area. The study findings are part of a broader project which includes a structured expert judgment on different hazard-related topics, including tsunami. The outcomes of this latter, which indicate that the chances of having waves larger than 1 m high on the NE coast of Thera have median probabilities of 50–60%, are relevant to the results of the present study.