The 2019 pumice raft and submarine eruption of Volcano F, Tofua-Kermadec Arc, from field spectroscopy, remote sensing and machine learning

The eruption of submarine volcanoes is a poorly-characterised source of marine hazard, largely due to the difficulty of observing such eruptions. Pumice rafts are a potentially-hazardous product of submarine volcanic eruptions: they pose danger to shipping, wildlife and impact livelihoods of those living in small island nations. However, our understanding of pumice rafts is limited due to rafting events often going unnoticed and occurring in remote areas. In this study, we analyse the pumice raft produced in the 2019 eruption of Volcano F in the Tonga Arc, southwest Pacific. We demonstrate that raft evolution, including waterlogging, can be detected using remote sensing methods, by identifying diagnostic spectral characteristics associated with saturated pumice. Using field spectroscopy, we observe unique spectral signatures in pumice samples, from this eruption and other eruptive settings, and compare these to the satellite-derived spectral measurements of the raft. We additionally show that pumice spectra are distinct from spectra of other floating debris.

These spectral signatures can be used to identify pumice from samples and remotely using satellites. Using pumice samples from the 2019 raft, collected at various distances from the vent of Volcano F, we show that samples that spent longer at sea are more eroded although their circularity remains similar regardless of collection location. We show that with increased time at sea, the raft thickness decreases, whilst its saturation and uniformity increase. Our study demonstrates that, beyond capturing the presence of pumice, spectral satellite analysis can be linked to pumice raft physical properties.

We detect two previously unreported eruptive periods at Volcano F, Tofua-Kermadec Arc, using a combination of satellite remote sensing and machine learning analysis of discoloured seawater. Additionally, we use the same methods to detect and observe submarine volcanic activity at Home Reef, Tofua-Kermadec Arc.