Probabilistic tsunami hazard assessment at Stromboli volcano: 1. Review of historical sources and expert elicitation findings

Abstract. Active volcanic islands, such as Stromboli in southern Italy, are sites where tsunamis generated by volcanic activity could be frequent and potentially destructive. Stromboli Island has experienced several landslides over the past decades, some of which have generated destructive tsunamis. This paper is part of a broader project aimed at developing a Probabilistic Tsunami Hazard assessment (PTHA) for Stromboli. We present here a review of historical tsunamis sourced from Stromboli, their correlation with explosive activity, and the results of an expert elicitation on tsunamigenic landslides.

In our review of historical tsunamis, we identified 16 events from 1879 to 2024, grouped into three classes based on the degree of inundation observed in the village of Stromboli, ranging from few ten to few hundred of meters inundation distances, the latter comparable to the widely documented December 2002 tsunami event. Four historical tsunamis (in 1879, 1921, 1924, and 1959 CE) have been critically discussed for the first time. Over the past 150 years, ~69 % = 11/16 of the catalogued tsunamis, with 90 % confidence [45 %, 87 %], were associated with paroxysms, while only ~27 % of historical paroxysms were associated with catalogued tsunamis, confidence [16 %, 40 %]. Similar conditional probabilities and uncertainty intervals were estimated from 1916 to 2025, excluding the tsunamis without significant inundation. The expert elicitation was divided in three parts. Part I provided estimates and uncertainty quantification of the number of tsunamigenic landslides at Stromboli (with volumes ≥ 1 × 10⁶ m³) in the past and of those expected in the next 50 years. Part II focused on the probabilities of different triggering mechanisms in the next 50 years. Part III quantified the probabilities of different tsunamigenic landslides (volume and positions) along the Sciara del Fuoco in the next 50 years. Results of the expert elicitation indicate that return periods of tsunamigenic landslides at Stromboli in the next 50 years have median values in the order of 10–12 years (with uncertainty from 3 to 50 years), and a median probability of their occurrence along the Sciara del Fuoco of either 82 or 86 % (depending on the weighting scheme used in the elicitation). Results of part III indicate slightly higher median probabilities for landslides occurring at elevation 300 to 700 m a.s.l. along the Sciara del Fuoco with volumes 1–5 × 10⁶ m³ as compared to other elevation and volume ranges.