[S-VC28] International volcanology

[SVC28-P04] The August 2019 Eruption of Volcano 0403-091, Tonga: results from seafloor sampling and observations undertaken 6 months after eruption

*Iona McIntosh¹, Isobel Yeo², Scott Bryan³, Matthew Dunbabin³, Kenichiro Tani⁴, Patrick Collins⁵ (1.Japan Agency for Marine-Earth Science and Technology, 2.National Oceanography Centre Southampton, UK, 3.Queensland University of Technology, Australia, 4.National Museum of Nature and Science, Japan, 5.Queens University Belfast, UK)

Keywords:Tonga, Submarine volcanism, Explosive volcanism, Pumice

Without warning, in 2019 Volcano 0403-091 (also known as Volcano F, 30 km NW of Vava’u in northern Tonga) erupted on the 7th August following 18 years of dormancy. The eruption produced a >200 km² pumice raft that was intercepted by two boats, causing navigational problems and hull abrasion. Pumice raft formation and evolution is poorly understood, yet rafts pose a range of potential hazards for marine traffic and infrastructure. The 7th August raft was imaged by satellites almost daily, so its source and path are well-constrained. This eruption therefore provided a unique opportunity to sample both rafted pumice with known float times and sunken pumice at the vent, as well as a rare chance to study vent structure, hydrothermal activity and marine life interactions immediately following an explosive, shallow marine eruption.

Here we present our findings from a rapid response survey of the submarine vent site, conducted 6 months after the eruption. The vent was investigated using a small Remotely Operated Vehicle (ROV), a small Autonomous Underwater Vehicle (AUV) and a surface glider, alongside a mini-dredge designed for operation from a small vessel. Video transects, bathymetry and sampling together enable characterisation of the seafloor eruption products, post-eruptive vent morphology, and the recovery of seafloor ecosystems 6 months after an explosive shallow submarine volcanic eruption. We present geochemical analyses of both seafloor (sunken) and raft material, identify the location of the new eruptive vent formed by 2019 activity, and characterise the volume and type of proximal seafloor deposits.

We highlight the successes of this small-scale, low budget survey using a locally hired small vessel in obtaining key samples and observations relatively rapidly after eruption. The January 2022 eruption of Hunga Tonga-Hunga Ha’apai is just the latest example of explosive activity at shallow submarine volcanoes in Tonga that lack detailed seafloor surveys, sampling or monitoring. Where survey safety conditions are acceptable, we encourage application of similar small scale survey methods to obtain vital information for assessing submarine volcanic hazards in Tonga and elsewhere.