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Decoupled gas bubbles and lava ponding: decoding the drivers of lava fountain dynamics and evolution through analogue laboratory experiments

Ariane Loisel1, Edward W. Llewellin2

  • Affiliations: 1Université de Strasbourg, CNRS, Institut Terre et Environnement de Strasbourg, UMR 7063, 5 Rue Descartes, Strasbourg F-67084, France; 2Department of Earth Sciences, Durham University, South Road, Durham, DH1 3LE, UK

  • Presentation type: Poster

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

  • Poster Board Number: 124

  • Programme No: 3.15.29

  • Theme 3 > Session 15

Abstract

Lava fountains are a common feature of mildly explosive basaltic volcanism. Their behaviour is influenced by the exsolved gas content in the rising magma and by the depth of lava ponding at the vent. Understanding this behaviour is of interest because it provides insights into subsurface processes and dictates the hazard lava fountains pose to those at-risk, such as volcano tourists. In this presentation, we share the results of analogue lava fountain experiments in which gas is injected into water flowing up a pipe, feeding a fountain. We explore how gas content, liquid flux, and depth of liquid ponding over the vent affect fountain dynamics. The injected gas forms discrete bubbles that rapidly ascend through the liquid column, greatly increasing both average fountain height and the amplitude of height fluctuations, resulting in unsteady fountaining. The presence of decoupled bubbles also qualitatively increases the degree of fragmentation of the fountain. On the other hand, we observe that increasing the depth of ponded liquid over the vent reduces both fountain height and fragmentation. Fountain steadiness remains largely unaffected by ponding, depending primarily on the gas volume fraction, as for the un-ponded case. Based on these results, we propose that the behaviour of natural lava fountains is a consequence of: 1) gas organization in the subvolcanic plumbing system, with decoupled gas bubbles driving pulsations; and 2) progressive ponding of lava retained within growing vent structures, which contributes to the gradual suppression of fountaining and volcanic activity.