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Direct observation of vesiculation dynamics in basaltic magmas via in-situ X-ray radiography

Barbara Bonechi1, Margherita Polacci1, Fabio Arzilli2, Giuseppe La Spina3,^ ^Jean-Louis Hazemann4, Richard Brooker5, Robert Atwood6, Sebastian Marussi7, Peter Lee7,8, Mike Burton1

  • Affiliations: 1Department of Earth and Environmental Sciences, University of Manchester, Manchester, UK; 2School of Science and Technology, Geology Division, University of Camerino, Camerino, Italy; 3Osservatorio Etneo, Istituto Nazionale di Geofisica e Vulcanologia, Catania, Italy; 4Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, Grenoble, France; 5School of Earth Sciences, University of Bristol, Bristol, UK; 6Diamond Light Source, Harwell Science and Innovation Campus, Harwell, Oxfordshire, UK; 7Department of Mechanical Engineering, University College London, London, UK; 8Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell, Oxfordshire, UK. 

  • Presentation type: Poster

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

  • Poster Board Number: 218

  • Programme No: 3.2.41

  • Theme 3 > Session 2

Abstract

Transitions in eruptive styles at basaltic volcanoes depend on the efficiency of gas-magma decoupling during ascent. Strong gas-melt coupling favours explosive eruptions, while weaker coupling promotes lava flows and fountaining. However, the mechanisms driving transitions between closed- and open-system degassing remain poorly understood due to limited direct observations of bubble dynamics under natural magmatic conditions. Here, we used a novel high-pressure/high-temperature X-ray Transparent Internally Heated Pressure Vessel apparatus combined with X-ray synchrotron radiography to perform in-situ experiments. These experiments enabled real-time, 2D observation and quantification of bubble growth and coalescence in basaltic magmas during decompression from 100 MPa to surface conditions. For low-viscosity magmas, bubbles coalesced and regained a spherical shape within 3 seconds, indicating that gas and melt remained coupled until the final ascent stage (i.e., the last hundred meters of the conduit), consistent with lava fountaining activity. In higher-viscosity magmas, slower bubble recovery facilitated the formation of connected pathways, leading to gas-melt decoupling. This behaviour was directly observed as bubbles expanded, connected to open pathways, and contracted as gas escaped. This study provides quantitative insights into bubble dynamics in basaltic magmas under pre- and syn-eruptive conditions. The novel apparatus advances our ability to observe degassing in real time, opening new frontiers in understanding magmatic processes. These findings are critical for improving our understanding of the mechanisms driving eruptive styles transitions and enhancing volcanic hazard assessment and risk mitigation strategies.