Explosive post-caldera collapse eruptions in the Kermadec-Tonga Arc

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Volcanic eruptions as ocean islands present a diverse range of direct and indirect hazards. Hunga Tonga-Hunga Ha'apai is a submarine collapse caldera along the Kermadec-Tonga arc with an active subaerial caldera rim cone. Volcanic activity renewed at Hunga Tonga-Hunga Ha'apai in December 2021 with activity developing a new vent at the NW caldera rim cone. At 04:14 UTC on January 15th 2022, the central caldera vent erupted with the most powerful eruption globally in the last 30 years. The eruption produced a 30 km-high and 4 km-wide ash column, barometric pressure waves that transited the Earth's atmosphere, a 6.5 MW earthquake and a trans-oceanic tsunami. Seafloor processes related to the eruption also severed local and international submarine telecommunication cables, which led to difficulties co-ordinating disaster response, effectively cutting off Tonga from international communications. The cascading hazards from the eruption caused $90.4M of damage, equivalent to 18.5% of Tonga's Gross Domestic Product. The eruption presented a geohazard blind spot in its rapid escalation from Surtseyan to Plininan-style eruption and generation of tsunami. It is important to understand the eruption and the cascading hazards. Whilst the eruption is notable for its power and cascading hazards, a significant question is the escalation in explosivity without warning remains a major question. Satellite evidence indicates that the active NE caldera rim cone was destroyed less than two hours before the eruption, posing a more specific question of its role in the escalation in eruption explosivity. Furthermore, the Kermadec-Tonga arc is populated by 28 similar collapse caldera volcanoes, thus an important question is whether the eruption at HT-HH likely representative of volcanism across the Kermadec-Tonga arc? This project proposes to bring together leading experts in multiple disciplines (including volcanologists, geochemists, marine sedimentologists, tsunami specialists and technologists). The project also utilises unique access to multiple different complimentary datasets that will allow the assembled partnership to answer these questions above.In order to address these important questions we will collate newly acquired high-resolution multibeam bathymetric data in April 2022 and August 2022 with partners NIWA and GNS. The comparison of this data with bathymetry from 2016 will allow us to identify seafloor changes caused by the eruption, calculate the volumes of material added or mobilised during this event, and derive eruption characteristics from the geomorphological changes mapped. This study provides a new baseline from which future larger studies of this potentially paradigm-shifting eruption can be based and the products generated will help to constrain the boundary conditions for future eruption and tsunami modelling. Evidence from similar settings (e.g. Anak Krakatau) indicate that the environment is incredibly dynamics, thus the project benefits from data collected as soon as is feasible after the eruption. This opportunity is unique both because of the scale of the event and because of the high-quality data available to study it (pre-existing bathymetry, cooperation from cable operators, well constrained eruption timings and processes) and also takes advantage of extending a scheduled research cruise nearby, significantly reducing the associated costs, CO2 outputs and COVID-19 exposure for international partners.