Ballistic projectile hazard of major explosions and paroxysms at Stromboli (Italy) with uncertainty quantification: 1. Mapping method and data analysis

Abstract. This study presents a novel method to map the areas affected by ballistic fallout generated by major explosions and paroxysms at Stromboli as well as quantitative analyzes of these areas. The mapping method is based on a simplified description of the affected areas by a circular proximal area and up to three circular sectors with variable radius and width, and uncertainty based on expert judgement. The dataset of maps includes a total of 67 events over ≈ 150 years, based on an extensive review of historical, observational, and monitoring data. Our findings highlight that 12 %–14 % of major explosions can exceed 1,000 m, and 29 % of paroxysms extend over 2,000 m of distance; (2) directional analysis of ballistic dispersal shows a predominant direction towards the East half-plane (87 %) for major explosions and towards the North half-plane (64 %) for paroxysms; (3) the average affected area was 6.9 × 10⁴ m² for major explosions and 3.6 × 10⁵ m² for paroxysms with a mean sector width of ≈ 90° for both categories. Notably, major explosions and paroxysms show a continuous distribution of maximum ballistic distance and area affected, suggesting the absence of a net separation between these two categories in terms of these products dispersal. Results highlight the limited influence of uncertainty in reconstructing the dispersal areas and stress the importance of volcanological monitoring. By quantifying distances, directions, and areas affected by ballistic fallout, we provide the necessary data, together with their uncertainty, to produce probabilistic maps of ballistic hazard presented in the companion study.