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Ash Fingers Without Aggregation: Insights from the July 23, 2024 Paroxysm at Etna Volcano

Carolina Díaz-Vecino1, Allan Fries1, Simon Thivet1, Simona Scollo2 , Riccardo Simionato1,3, Jonathan Lemus1,3, Costanza Bonadonna1

  • Affiliations:  1 Département des Sciences de la Terre, Université de Genève, Genève, Suisse 2 Istituto Nazione di Geofisica e Vulcanologia, Osservatorio Etneo, Catania, Italy 3Département d\'Informatique, Université de Genève, Carouge, Suisse 

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 89

  • Programme No: 3.12.15

  • Theme 3 > Session 12

Abstract

Ash fingers are descending particle-laden plumes that develop underneath volcanic clouds and have been observed to form during several volcanic eruptions worldwide. Similar to volcanic ash aggregation, these features drive the rapid collective settling of volcanic ash particles, affecting their sedimentation behaviour in the atmosphere and representing a significant source of uncertainty in forecasting ash dispersion following explosive eruptions. However, obtaining accurate measurements of ash fingers properties remains challenging, as they are visible only under certain eruptive and atmospheric conditions that are not well defined yet. Also, ash fingers are poorly constrained from post-event analysis of deposits, which can be characterised by bimodal grain size distributions in case of  ash aggregation. To date, the field quantitative description of ash fingers remains limited, emphasising the importance of improving their characterisation through further field studies. This study focuses on ash fingers formed during a paroxysm event at Etna volcano (Italy) on July 23, 2024, using high-resolution (HR) video footage captured during the eruption. Notably, this event is particularly significant as no ash aggregation was observed, allowing us to isolate the deposit signature of ash fingers without the effects of aggregation. We analysed key finger characteristics, including downward velocity, width and spacing, and complemented these observations with measurements of tephra deposition performed simultaneously directly in the fallout, like sedimentation rates and grainsize distribution. This study offers new insights into the dynamics of ash fingers in the absence of aggregation, advancing our understanding of their part in ash dispersion and sedimentation processes.