Expedition Report: Exploring recent volcanic activity in the Lau Basin for iMAGE-CREATE
The Hunga Tonga volcano is located along the Tonga-Kermadec arc of the SW Pacific, where the Pacific plate subducts beneath the Indo-Australian plate at rapid rates nearing 24cm/year. This volcano erupted in January 2022 in spectacular fashion, with an eruptive force that appears to rival that of Krakatoa (1883), and has been calculated to have experienced an explosive force with a magnitude that exceeds the largest thermonuclear bomb ever tested (in excess of 60 megatons of TNT). This eruption wiped out the subaerial volcanic cone, leaving behind only a crater of roughly 4km in diameter, and at water depths of roughly 800 mbsl. The shockwave of this eruption was heard in Alaska, 10000km away, and tsunami waves washed upon the nearby kingdom of Tonga, as well as Peru, leading to at least 3 casualties.
I was asked to partake in a research expedition led by New Zealand’s Dr. Cornel De Ronde of the Institute of Geological and Nuclear Science Limited (GNS) aboard the R/V Tangaroa. This research cruise set out to explore the Hunga Tonga edifice and surrounding volcanic mounds in order to better understand the sequence of events leading up to the eruption and also to characterize the post-eruptive effects on the crater in terms of volcanic and hydrothermal activity there.
This cruise employed multiple methods of analysis to characterize these sites, beginning with ship-based multibeam bathymetry, with a magnetometer in tow. A ship-based gravimeter was also utilized to simultaneously acquire gravity data. Afterwards, 11 parallel and perpendicular seismic survey lines were collected across the volcano and surrounding cones. Thereafter, CTD (conductivity, temperature, depth) surveys were accomplished through a combination of vertical and tow-yo casts. Finally, dredging of the volcanic features was utilized to collect a wide range of samples from Hunga and the surrounding cones.
My work aboard the research vessel was primarily focused on dredging. I worked with a team of petrologists to categorize and characterize the samples collected from the dredge in terms of the mineralogical and textural qualities. We collected 278 rock samples over four days of dredging, with a total of 34 dredges. Additionally, I was also involved in CTD deployment and data entry, and was tasked with managing the daily log of activities from noon to midnight. Finally, I frequently volunteered my time to the multibeam technicians, to help “clean” the active dataset through Qimera software.
The Hunga Tonga volcanic eruption is significant as it provides potential insights into the eruption style of early earth volcanoes. Earth has been on a cooling trend since its initial formation, as heat is lost through volcanic activity and conduction. Therefore, the early earth used to be significantly hotter than today, and as a result, volcanic activity was more abundant, and tectonic plate motion rates were likely much faster than our present day. Rapid rates of plate convergence in the early Earth may be comparable to the rapid plate motion rates that we see along the Tonga-Kermadec arc, and therefore this arc offers the most ideal natural laboratory for investigating early Earth volcanic systems. These hypotheses are supported by the presence of boninitic lavas on the surrounding volcanic cones around Hunga Tonga. The sequence of events leading up to the volcanic eruption is not necessarily apparent. A typical volcanic eruption along an oceanic arc may occur following the drainage of a magma chamber, which creates a vacuum force, drawing in water, and inspiring a phreatomagmatic eruption; however, there is little to no evidence to suggest such a drainage event at Hunga, and investigations into this eruption style are ongoing, but may be a result of over-pressurization of magmatic volatiles facilitated by an impermeable anhydrite cap rock.
My role on this expedition was primarily to investigate the region for hydrothermal activity. Although no black smoker chimney samples were acquired via dredging, there is strong supporting evidence to suggest active volcanic and hydrothermal activity persisting at Hunga Tonga. Future research in this area will hopefully involve the use of a remotely operated vehicle (ROV) to acquire samples, which will elucidate the post-eruptive processes that may contribute to hydrothermal activity in terms of the mineralogy, and magmatic volatile contributions in these incredibly juvenile deposits.
