The colossal eruption of the Hunga Tonga–Hunga Haʻapai volcano in the Kingdom of Tonga on Jan. 15, 2022, was the largest recorded in the modern satellite era, sending a plume 58 kilometers high and a pressure wave around the globe. While the atmospheric effects were immediately visible, new research reveals the eruption also triggered the fastest and most powerful underwater flows ever measured. These immense currents, a type of submarine avalanche, raced across the seafloor, destroying telecommunication cables and traveling more than 100 kilometers. The event has provided scientists with a rare, direct look at the immense geological forces that reshape the deep ocean floor, a process that usually occurs unobserved.

Four months after the eruption, a scientific expedition used remotely operated vehicles to survey the seabed west of the volcano. Researchers discovered vast deposits of volcanic ash and rock, known as volcaniclastic deposits, blanketing the seafloor at nine different sites. These layers, ranging from seven to 150 centimeters thick, were the remnants of at least two massive submarine density currents. Such currents are powerful, fast-moving flows where a mixture of sediment and water moves downslope under the force of gravity. The Hunga currents were so forceful that they not only carried material from the collapsing volcano but also scoured the existing seabed as they traveled across the Lau Basin.

To reconstruct the journey and dynamics of these currents, scientists analyzed the microscopic contents of the sediment cores they collected. The key to the investigation lay in microfossils, the tiny, intricate skeletons of single-celled marine organisms like foraminifera and radiolaria. By studying the mixture of different microfossil populations within the deposits, researchers could determine where the sediment originated and what it picked up along its path. The presence and physical condition of these tiny fossils provided clear evidence that the currents were still highly erosive even 80 kilometers from their source, acting as a geological sandblaster that remobilized older seafloor sediments.

The findings, published in the journal Geochemistry, Geophysics, Geosystems, have significant implications for understanding both natural and human-made impacts on the deep sea. The massive, rapid burial of the seafloor likely suffocated entire ecosystems that rely on chemosynthesis, a process where organisms use chemicals from hydrothermal vents for energy instead of sunlight. This event serves as a stark, large-scale model for the potential effects of activities like deep-sea mining, which can create sediment plumes that smother marine life. Furthermore, by demonstrating how effectively these currents transport organic-rich material, the study suggests that major volcanic eruptions may play a greater role in moving carbon into deep ocean basins than previously understood, influencing the global carbon cycle.

References

• Brown, L. & University of Oregon. (2025, July 2). Ocean eruption leaves deep-sea creatures gasping as ash clouds blanket the seafloor. Phys.Org; University of Oregon. https://phys.org/news/2025-07-ocean-eruption-deep-sea-creatures.html

• Chaknova, M., Giachetti, T., Paredes‐Mariño, J., Soule, A., Van Eaton, A. R., Beinart, R., Crundwell, M., Cronin, S. J., Jutzeler, M., Fauria, K. E., Clare, M. A., Yeo, I. A., Arellano, S., Kelly, L., Watson, S., Carey, R., Kula, T., & Young, C. M. (2025). How did westward volcaniclastic deposits accumulate in the deep sea following the january 2022 eruption of hunga volcano? Geochemistry, Geophysics, Geosystems, 26(4), e2024GC011629. https://doi.org/10.1029/2024GC011629