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A broadly homogeneous magma reservoir evacuated during catastrophic submarine caldera collapse of Hunga Volcano, 15 January 2022 Tonga

Jie Wu1,2, Marco Brenna 1\, Shane Cronin2, Ingrid Ukstins2, David Adams2, Joali Paredes-Mariño2, Kyle Hamilton2,3, Mila Huebsch2

  • Affiliations: 1Department of Geology, University of Otago, Dunedin, New Zealand; 2School of Environment, University of Auckland, Auckland, New Zealand; 3School of Earth & Atmospheric Sciences, Queensland University of Technology, Brisbane, Australia. 

  • Presentation type: Poster

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

  • Poster Board Number: 40

  • Programme No: 1.7.27

  • Theme 1 > Session 7

Abstract

We present integrated geochemical results of whole-rock and microlite-poor glass for the 15 January 2022 Hunga eruption based on tephra deposits and submarine-sampled bombs and spatter spanning the entire eruptive sequence. Whole-rock samples from the 2022 eruption are andesite (56.5--59.1 wt% SiO2), while glass extends to more evolved compositions (56.6--65.6 wt% SiO2). The pre-climax (stage 1) glass is the most evolved with the highest SiO2, K2O, K2O/TiO2 and the lowest MgO and CaO/Al2O3. The main fall phases (stage 2--9) and the wanning phase (stage 10) have slightly less evolved glass compositions, with relatively small compositional fluctuations. Glass compositions are mainly divided into three groups, including low-Ti, low-K (group 1; dominant), high-Ti, high-K (group 2), and low-Ti, low-K (group 3). Group 1 is further subdivided into high-Mg (1a) and low-Mg (1b) subgroups. Group 1a represents the least evolved compositional group, which is the dominant glass population in all stages except the pre-climax stage. Group 1b is slightly more evolved compared to 1a and is only present in the first two stages. Both groups 2 and 3 are more evolved, with group 3 being depleted in FeO. Common swirly glass textures reveal melt mixing/mingling between groups 1 and 3. Our results suggest that the Hunga eruption tapped multiple melt lenses of broadly homogenous magma with minor heterogeneities controlled by variable crystallization of clinopyroxene and plagioclase. Additional inputs from a shallower smaller reservoir (group 1b), evacuated mostly during the early stages of eruption.