Abstract
On January 15th, 2022, the submarine caldera volcano Hunga, in the Kingdom of Tonga, created an extremely high eruption plume (55-57 km) dominated by ash-sized material and a high water/aerosol content. The fall distribution, extending at least 260 km from the volcano, and fine grainsize, with 36 wt.% (+ or - 5 wt.%) of analyzed ash finer than 63 mu m, contrast with typical Plinian eruptions. The measured observations of this eruption do not fit current models of eruption column generation and energy release, possibly due to poorly understood magma-water interaction processes. External water may amplify magma fragmentation and bolster explosivity, in a feedback loop between micro-fragmentation and ongoing direct contact between magma and water. During such a large-scale event, variable rates and styles of magmawater interaction can occur over time and space, in different water depths and sub-sea floor confinement conditions. Pyroclastic products and syn-eruption observations across subaerial, shallow subaqueous, and deep subaqueous stages of the 2022 Hunga eruption provide a unique opportunity to explore the diverse modes of magma-water interaction. We present textural analysis of internal crystal and vesicle distributions, and particle surface morphology, using 3D X-ray tomography data ( approximately 15 mu m resolution) obtained at the Australian Synchrotron, supplemented by 2D SEM imagery ( approximately 100 nm resolution). These analyses are used in combination with in situ geochemical analysis by electron probe microanalysis to identify syn-eruptive magma crystallization, gas exsolution, and fragmentation processes. Additionally, volatile concentrations including H (sub 2) O and CO (sub 2) in groundmass glass are used to estimate changes in viscosity and ultimately assess explosive potential. By comparing pyroclastic products of each style of activity at Hunga, we explore the varying consequences of rapid quenching on eruption dynamics and the significance of primary and secondary fragmentation in submarine explosive eruptions.