Future eruptions of the Kolumbo volcanic field: prognosis with hazard and risk assessment

The Kolumbo submarine volcanic field consists of at least 24 monogenetic cones and a polygenetic central volcano which erupted in 1650 CE. The prognosis, hazards and risks from future eruptions are assessed by structured expert judgement informed by knowledge of the volcanic history, structure and eruptive products, hazards modelling and global knowledge of submarine volcanism. There are significant knowledge gaps leading to large uncertainties in this assessment, characterised quantitatively by 90% uncertainty intervals (UI) in elicitation responses. The median assessed probability of eruption in the next 30 years is low at 0.75% (90% UI 0.4% to 14%) but the upper, 95th percentile value indicates the probability could be as high as 1 in 7 chance. The magnitude of an eruption in the next 30 years is mostly likely to be smaller than that of 1650 CE, but there is a significant chance it could be as large as 1650 CE. A future eruption could generate several high impact hazards including tsunamis, lethal gas clouds, pyroclastic density currents, widespread tephra fall and associated earthquakes. Nearby islands are threatened and in particular Santorini. In the tourist high season, the exposed population on Santorini may exceed 80,000 people. Vulnerability is high especially along the eastern coast which may be affected by tsunami and gas cloud hazards. Transport, telecommunications, power supplies and water resources are likely to be severely disrupted and even cease to function. For tsunami hazards individual risk of death in threatened areas is high and societal risk is very high if there is an ongoing eruption and exceeds what might be judged acceptable by factors of over 100.