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Mush disaggregation and dike propagation timescales at active volcanoes -- Evidence from the 2022-2023 Fagradalsfjall eruptions

Alberto Caracciolo1, Edward W. Marshall1, Euan J. F. Mutch2, Enikő Bali1, Sæmundur A. Halldórsson1, Simon Matthews1, Olgeir Sigmarsson1, John Maclennan3, Heini Merrill1, Bryndís Ýr Gisladóttir1, Sóley Johnson1, Maren Kahl4, Guðmundur H. Guðfinnsson1, Jóhann Gunnarsson Robin1, Rebekka H. Rúnarsdóttir1

  • Affiliations: 1 Nordic Volcanological Centre, Institute of Earth Sciences, University of Iceland, Reykjavík, Iceland. 2 Earth Observatory of Singapore, Nanyang Technological University, Singapore 3 Department of Earth Sciences, University of Cambridge, Cambridge, UK 4 Ruhr-Universität Bochum, Institute for Geology, Mineralogy and Geophysics, Bochum, Germany 

  • Presentation type: Poster

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

  • Poster Board Number: 264

  • Programme No: 1.3.12

  • Theme 1 > Session 3

Abstract

The 2021-2023 Fagradalsfjall eruptions provide a unique perspective on the initial stages and temporal evolution of a basaltic magma plumbing system, since its previous eruptions occurred 7,000 years ago. In this work, we focus on the 2022 and 2023 Fagradalsfjall eruptions, integrating our petrological and geochemical dataset with data from the 2021 Fagradalsfjall eruption. We show that the 2022 and 2023 Fagradalsfjall eruptions were sourced from a near-Moho magma domain at ~14 km depth, similar to the 2021 Fagradalsfjall eruption. However, clinopyroxene-melt barometry suggests that the 2022 and 2023 magmas experienced crystallization either in an embryonic mid-crustal reservoir or during slow ascent within the magma conduit. Olivine and plagioclase crystals constitute two different populations in the crystal cargo, with their diffusion timescales representing two different processes. Plagioclase diffusion timescales reveal the erosion of crystal mushes, a process that unfolded over the months and days prior to the 2022 and 2023 eruptions. The progressive shortening of these timescales from 2021 to 2023 suggests an increasingly rapid response of the magmatic system to deep melt injections. In contrast, olivine diffusion timescales capture the timing and duration of dike opening and propagation from near-Moho depths, as evidenced by the strong correlation between their cumulative frequency distribution and pre-seismic activity. Combined geophysical, petrological, and barometric data suggest that the 2022--2023 propagating dikes took considerably more time to traverse the lower crust and reach mid-crustal levels than the upper crust which was breached within a few days through a fully established magma pathway.