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A New Subaerial Record of Explosive Volcanism and Tsunami along the Tonga Volcanic Arc, Tonga, SW Pacific

Annahlise Hall 1, Shane Cronin1, Geoffrey Clark2, David Sear3, Phil Shane1, Taaniela Kula4

  • Affiliations:  1School of Environment, University of Auckland, Auckland, New Zealand; 2Department of Archaeology and Natural History, Australian National University, Canberra, Australia; 3School of Geography and Environmental Science, University of Southampton, Southampton, UK; 4Government of Tonga, Ministry of Lands and Natural Resources, Tonga Geological Services, Nuku'alofa, Tonga 

  • Presentation type: Talk

  • Presentation time: Friday 10:30 - 10:45, Room R280

  • Programme No: 3.4.7

  • Theme 3 > Session 4

Abstract

Despite frequent volcanic activity, the eruption history and hazards of the Tonga Volcanic Arc remain poorly constrained due to the small landmass of the Tongan archipelago (~750 km²) and limited Holocene subaerial exposures. This study presents a new tephrochronological record of explosive eruptions and tsunami events in Tonga, based on swamp coring across uplifted and inhabited islands east of the volcanic front and downwind for high-altitude winds. These swamps, formed in lagoon basins isolated after the mid-Holocene high sea level stand, preserve tephra layers well compared to the surrounding tropical soils. Coring revealed multiple tephra layers within humic sediment or peat, with radiocarbon dating providing a timeline of eruptions within the last 6500 cal. Years B.P. Geochemical analysis indicates explosive eruptions of basaltic andesite to dacite composition (55-69 wt.% SiO₂), with some exhibiting compositional changes during the eruption. Preliminary results suggest several significant eruptions, including two from Hunga volcano (AD 418-645 and AD 1119-1279), likely generating tsunamis, as indicated by sandy layers with shell fragments and volcanic particles. Notably, the tephra properties of the AD 500 eruption closely resemble the 2022 Hunga eruption, though deposit thicknesses suggest it was a larger event. Further analysis suggests another major eruption between AD 1000-1300, likely from Tofua or Kao, with widespread impact. This study improves the understanding of volcanic and tsunami hazards, crucial for assessing future risks, especially on Tongatapu Island, where >70% of Tonga's population resides. Ongoing work will refine eruption chronologies and correlations and link findings with archaeological records.