Program uses Singapore Time and is 8 hours ahead of GMT

Special Session 02 Wed-03 Aug 18:00 – 20:00

Extreme Explosivity of the 15 January 2022 Hunga Eruption, Tonga, Driven by Edifice Failure, Caldera Collapse and Magma-water Interaction.

Hunga Volcano in Tonga comprises a ~5 km-diameter caldera 140-150 m below sea-level. Historical Surtseyan eruptions occurred along caldera ring faults. The latest eruption began on 20 Dec 2021, near the 2014-15 vent. A >20 km high plume formed on 14 Jan 2022. On 15 Jan the climactic event was the largest explosion ever digitally recorded at peak eruption rate of ~109 kg/s. The event produced global air-pressure waves, tsunami and a >50 km-high eruption column. The whole pumice composition was similar to past events; 56 wt% SiO2 andesite. Mingled, crystal and microlite-poor glass spans 56-63 wt% SiO2 over micron-to mm scales. Up to ~10% volcanic/hydrothermal xenoliths occur. The fall deposit at 65-80 km is poorly sorted and fine-grained (4-7 wt% <1 mm). Juvenile clasts are dense (>2.7 g/cm3), with isolated vesicles. Minor <2-10% lower density (0.8-2.0 g/cm3) scoria lapilli (dmax 15 mm) fell out first. High-resolution SEM image counts show 70% of particles with hackle lines, stepped fractures, branched and conchoidal fractures. Dendrogrammatic statistical tests classify the curviplanar Tonga particles together with ash of the 2012 submarine Havre eruption. Properties of the juvenile tephra, along with the first observational insights from the vent area, show that the eruption was driven by shallow volcano-tectonic and hydrological processes. Available evidence suggests that edifice failure caused collapse and sudden caldera subsidence. Magma was rapidly squeezed from a hot and compositionally heterogeneous reservoir. Magma was fragmented very efficiently through sea-water infiltration into the edifice. The proportion of hackled/stepped fracture surfaces is higher than from recent major submarine eruptions. Subsequent post-eruption earthquakes suggest stepwise, piston-like subsidence of the magma reservoir, or magma re-injection.

Professor Shane Cronin is a volcanologist at the University of Auckland, New Zealand. His research speciality is physical volcanology, volcanic sedimentology, volcanic hazards and the impacts of volcanism on agriculture, infrastructure and health. He completed his PhD in 1997 at Massey University and a Post-Doctoral Fellowship at the South Pacific Applied Geoscience Commission in Fiji (1997-2000). He was an Alexander Von Humboldt Fellow based in Germany (and Vanuatu) from 2001-02 and began as Lecturer at Massey University from 2003, being promoted to Professor in 2009. In 2015 he moved to the University of Auckland as Professor and Director of the NZ National Science Challenge in Resilience. Prof Cronin has led many major research programmes on volcanic and other natural hazard from major grant agencies in NZ, Korea, Indonesia and the SW Pacific (totalling >$35 million in collective funding). He has supervised over 40 PhD students and >20 post-doctoral fellows. He is active in public education and as a volcanic commentator in the media. He has published over 220 scientific papers in international journals, including Nature Geoscience, Nature Communications and Geology. His research and publications include many volcanology works based in the SW Pacific, including on Fiji, Vanuatu, Samoa, Solomon Islands and Tonga. Prof Cronin has worked in Tonga for over two decades, conducting research with Tongan geologists on Fonuelei, Late, Tofua, Kao and Hunga volcanoes as well as on volcanic ash fall records from down-wind islands