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In-flight fragmentation dynamics in explosive eruptions of low-viscosity magmas

Clothilde Biensan1,6 , Jacopo Taddeucci1,  Miguel Alatorre-Ibarguengoitia2,  Piergiorgio Scarlato1, Daniele Andronico3, Tullio Ricci1, Elisabetta Del Bello1, Luca D'Auria4,5, Maria Asensio-Ramos5, Danilo Mauro Palladino6

  • Affiliations: 1Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Via di Vigna Murata 605, 00143 Roma, Italy 2Instituto de Investigación en Gestión de Riesgo y Cambio Climático, Universidad de Ciencias y Artes de Chiapas, Libramiento Norte poniente 1150, Lajas Maciel, Tuxtla Gutiérrez, 29039 Tuxtla Gutiérrez, Chiapas, México 3Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, P.zza Roma 2, 95125, Catania, Italy  4Instituto Tecnológico y de Energías Renovables (ITER), 38600 Granadilla de Abona, Tenerife, Canary Islands, Spain  5Instituto Volcanológico de Canarias (INVOLCAN), 38320 San Cristóbal de La Laguna, Tenerife, Canary Islands, Spain 6Sapienza-Università di Roma, Dipartimento di Scienze della Terra, Piazzale Aldo Moro 5, 00185, Rome, Italy 

  • Presentation type: Talk

  • Presentation time: Tuesday 15:00 - 15:15, Room S150

  • Programme No: 3.2.8

  • Theme 3 > Session 2

Abstract

Volcanic bombs---coarse fragments of low-viscosity magma ejected during explosive eruptions---offer critical insights into eruptive dynamics and hazards. Traditionally, fragmentation has been attributed to conduit processes; however, our research highlights the significant role of in-flight fragmentation in influencing bomb size, trajectory, and dispersal. By analyzing high-speed, high-resolution videos of eruptions at Tajogaite volcano in La Palma, Canary Islands (fountaining and spattering activity); Mount Etna, Sicily (fountaining activity); and Stromboli, Aeolian Islands (strombolian activity), we identified four distinct in-flight fragmentation mechanisms: (i) inflating fragmentation, i.e. pyroclasts expand and fragment, revealing hotter interiors; (ii) deformation fragmentation, characterized by stretching, bending, and rotation before break-up; (iii) detaching fragmentation, which involves breakage without visible deformation; and (iv) collision fragmentation, resulting from interactions between pyroclasts of varying sizes and velocities. In-flight fragmentation affected from 9% to 48% of the observed bombs. Deformation fragmentation was predominant during Tajogaite fountaining (66%) and Strombolian activity (86%), while collision fragmentation was more common in Tajogaite spattering (72.5%) and Etna fountaining (49%). Within the deformation mode, stretching was the most frequent sub-type, with inflating and detaching fragmentation occurring less often. Drag force plays a pivotal role in in-flight fragmentation by inducing or amplifying velocity gradients within bombs, especially in larger, faster fragments with irregular shapes. This increased drag enhances deformation, localizes stress, and promotes instabilities that can lead to fragmentation. These findings underscore the importance of in-flight fragmentation in determining pyroclast deposition, particularly in mafic eruptions and provide valuable insights for refining ballistic hazard models and improving interpretations of volcanic deposits.