Decades long priming of plumbing system preceding the 2022 eruption of Hunga Tonga Volcano, Tonga

Hunga Tonga volcano, located in the Kingdom of Tonga in the southwest Pacific Ocean northeast of New Zealand, forms part of the Tonga–Kermadec subduction zone and is renowned for its VEI 6 eruption in 2022, the most explosive volcanic event of the past century. This cataclysmic eruption generated a volcanic plume rising to >58 km into the mesosphere and injected an unprecedented amount of water vapour into the upper atmosphere.Here, we investigate the complex zoning patterns of clinopyroxene phenocrysts from tephra ejected in the 2022 eruption by integrating textural analysis, thermobarometry, and Fe–Mg diffusion chronometry. Clinopyroxene cores range from diopsidic to augitic compositions and commonly display sieved and patchy textures, indicating extensive antecryst recycling and dissolution–recrystallization processes. Multiple growth bands with diopsidic to augitic compositions record repeated magma-mixing events and variable degrees of chemical homogenization within the shallow reservoir.Preliminary diffusion modelling indicates that the time elapsed between mafic magma injection and eruption spans from decades to a few months, with only a minor population of crystals recording timescales shorter than one month. These results suggest the absence of a direct temporal link between shallow magma mixing and the immediate trigger of the 2022 cataclysmic eruption at Hunga Tonga. We propose a decade-long pressure build-up process instead, with repeated mafic injections and magma and gas accumulation up to a few months before the eruption, in agreement with the top-down/decompression-driven trigger model of Wu et al. (in review).