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A volcanic bomb as a natural laboratory: insights on melt evolution driven by swift crystallization kinetics during the 2022 Hunga eruption, Tonga

Jie Wu1,2, Alessio Pontesilli 3, Marco Brenna1, Shane Cronin2, Sung-Hyun Park4, Joali Paredes-Mariño2, Kyle Hamilton2,5, David Adams2

  • Affiliations: 1Department of Geology, University of Otago, Dunedin, New Zealand; 2School of Environment, University of Auckland, Auckland, New Zealand; 3Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy; 4Korean Polar Research Institute, Incheon, Republic of South Korea; 5School of Earth & Atmospheric Sciences, Queensland University of Technology, Brisbane, Australia. 

  • Presentation type: Poster

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

  • Poster Board Number: 204

  • Programme No: 3.2.27

  • Theme 3 > Session 2

Abstract

The 15 January 2022 Hunga eruption was globally impactful, partly due to its submarine setting. This setting also allowed the rapid chilling of pyroclastics and unique insights into natural crystallization dynamics. Using chemical and textural gradients in a zoned Hunga volcanic bomb dredged from the inner submarine caldera, we infer crystallization kinetics and apply thermal modelling to reconstruct cooling history. From bomb rim to core, increasing microlite crystallization drove progressive groundmass glass composition from low-Si andesite to high-Si dacite, closely reproducing compositional variations within tephra from the entire eruptive sequence. This reflects extremely rapid crystallization kinetics, indicated by increasing degrees of chemical and textural disequilibrium of clinopyroxene and plagioclase microlites towards the bomb interior. Swift kinetics are also shown by high crystal growth rates resulting from interaction with water. Our results demonstrate that crystallization processes far outside equilibrium conditions have a pivotal role in driving post-fragmentation melt evolution. These suggest caution must be applied when applying experimentally-derived crystal growth rates to natural cooling processes, as well as interpreting glass compositional variations in terms of liquid lines of descent, and selecting appropriate glass shards for distal tephra identification studies.