The most explosive volcanic event in >100 years occurred in January 2022, when Hunga Tonga-Hunga Ha'apai (HTHH) erupted unexpectedly, triggering cascades of hazards1. The atmospheric shockwave was felt around the planet, tsunamis inundated coastlines, and communications were cut when seafloor cables were damaged. Unique datasets were acquired before and after the eruption, providing the first opportunity to study the hazard cascades created by such a powerful event. New seafloor and subsurface geophysical data, acquired three months after the eruption, enable comparison with pre-eruption data, to show how the volcano evolved and shaped the surrounding seafloor. Initial analysis reveals that powerful pyroclastic density currents were generated following the initial eruption, sculpting deep seafloor channels and travelling vast distances. These surges may be the main trigger for tsunamis and responsible for >100 km of damage to seafloor cables; however, this requires validation. Coring of the seafloor and on onshore islands will provide the necessary sedimentological constraint to the eruptive timeline. This timely project offers a unique opportunity to determine the distribution, timing, behavior and impact of pyroclastic flows, the linked and cascading hazards associated with such a major eruption, and new insights into many other volcanoes worldwide that pose similar hazards.
The project has the following objectives:
 First quantified impact of such a major eruption on the seafloor. High-resolution bathymetric data acquired in 2015 and March 2022 (and planned for 2024) will be analysed using ArcGIS/QGIS to quantify elevation and erosional/depositional changes, map pyroclastic flow pathways using morphometric analysis, integrating locations of cable damage. Topas profiles that image c.50 m below seafloor will be analysed in Petrel to map deposit geometries.
 Develop an eruption timeline to establish precursor events and hazard cascades. Seafloor and terrestrial cores acquired in 2022 will be analyzed to determine the sedimentology of deposits and develop a timeline of events before, during and after the eruption. SEM, X-Ray Imaging, MSCL and geochemical analysis of volcanic products will enable differentiation of deposit types and characterization of the dynamics of pyroclastic flow-water interactions to test experimental laboratory models2.
 New model for hazard cascades at volcanic islands. Results of 1 and 2 will be integrated to test established models of volcanic eruptions and pyroclastic flow-water interactions, and to develop a new model of hazard cascades at similar volcanoes3. A GIS-based review of volcanic islands and seamounts will determine equivalent systems worldwide, identifying potential future risk hotspots.
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at National Oceanography Centre Southampton within the vibrant Ocean BioGeosciences group. The student will become part of two NERC-funded projects on volcanic hazards across the Tonga Arc that include international academic, industry and government partners and will have the opportunity to travel to New Zealand to analyse data. Specific training relevant to a future academic career as well across a range of industries (e.g. geohazard assessment, offshore survey and engineering and reinsurance) include:
1. Core logging and analysis (SEM, X-Ray Imaging, MSCL, XRCT)
2. Geophysical data acquisition, processing and interpretation
3. Geochemical and radiometric sample analysis and interpretation
4. GIS, seafloor mapping and data analysis