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Surface analyses of the ash from the 2021 Tajogaite eruption, La Palma, reveals compositional diversity and complex formation pathways of fluoride-bearing compounds

Pierre Delmelle 1, Julia Eychenne2,3, Mickaël Laumonier2, Elena C. Maters4, Arnaud Denis1, Séverine Moune2, Matthew J. Pankhurst5,6

  • Affiliations: 1Earth & Life Institute, UCLouvain, Louvain-la-Neuve, Belgium; 2Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, F-63000 Clermont-Ferrand, France; 3Université Clermont Auvergne, CNRS, INSERM, Institut Génétique, Reproduction et Développement, F-63000 Clermont-Ferrand, France; 4Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK; 5Instituto Volcanológico de Canarias (INVOLCAN), San Cristóbal de La Laguna, Tenerife, Spain; 6Instituto Tecnológico y de Energías Renovables (ITER), Granadilla de Abona, Tenerife, Spain

  • Presentation type: Poster

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

  • Poster Board Number: 23

  • Programme No: 6.6.11

  • Theme 6 > Session 6

Abstract

The presence of soluble fluoride in volcanic ash fallout often raises environmental and health concerns. Numerous studies have reported notable concentrations of fluoride in ash leachates, sparking diverse interpretations regarding the composition and formation mechanisms of fluoride-bearing compounds in volcanic ash and their associated hazards. The 2021 eruption of Volcán de Tajogaite, Cumbre Vieja, La Palma, provided a unique opportunity to investigate the occurrence of fluoride-bearing compounds on ash surfaces over an 85-day period of ash emissions. This study presents detailed surface analyses (using high-resolution SEM-EDX and XPS) of fresh ash samples representative of the entire duration of the eruption. Our findings reveal a remarkable diversity in the composition of fluoride-bearing compounds on the ash particles. Both soluble (alkaline and alkaline-earth metal salts) and poorly-soluble fluoride (hexafluoroaluminates) species were identified, with their relative abundances varying significantly across the analysed samples. We suggest that this complexity primarily reflects the temperature conditions governing in-plume interactions between the ash surface and the magmatic gas phase. Additionally, the island setting of the eruption likely contributed to the chemical diversity through the incorporation of marine aerosols into the hot volcanic gas-ash mixture. Our conclusions diverge from prior interpretations of the leachate compositions of Tajogaite ash, with significant implications for inferring the potential environmental and health hazards posed by the ash deposits on La Palma island.