The 2022 Hunga-Tonga eruption triggered fast and destructive submarine volcanic flows, according to new research
In January 2022, the eruption of the submerged Hunga Tonga–Hunga Ha’apai volcano triggered a fast-moving and destructive underwater debris flow that severed telecommunication cables and reshaped the surrounding seafloor.
The findings – representing some of the first fieldwork to document what happens when large volumes of erupted volcanic material are delivered directly into the ocean – provide new insights into the behaviour and hazards of submerged volcanoes.
Explosive volcanic eruptions on land create pyroclastic flows of hot ash and rock that, when they reach the ocean, can trigger damaging tsunamis, surges, and turbidity currents.
This creates hazards for underwater infrastructure and marine biological communities.
However, it is estimated that the majority of Earth’s volcanoes are underwater.
Despite this, explosive underwater eruptions are poorly understood, limiting the grasp of associated risks.
Volcaniclastic flows
Michael Clare, of the UK’s National Oceanography Centre in Southampton, and colleagues, addressed the knowledge gap by evaluating observations of underwater volcaniclastic flows triggered during the 2022 Hunga eruption in Tonga, which destroyed nearly 200km of crucial subsea telecommunications cables.
Combining data from the timing and extent of cable breaks, repeated bathymetric surveys, eruption observations, and rock core sampling, Clare et al show that the rock and ash ejected during the Hunga eruption collapsed vertically and directly into the ocean and travelled as an extremely fast-moving and highly destructive underwater debris flow.
According to the findings, the submarine density current travelled more than 100km across the seafloor, reaching speeds of 122km per hour.
What’s more, the volcanoclastic currents reshaped the seafloor around the Hunga volcano, excavating greater than 100m-deep scours and channels into the surrounding seabed.
Similar landforms observed around many other submerged volcanoes suggest that powerful underwater flows have occurred during large eruptions at other sites worldwide.
Writing in a related perspective, Rebecca Williams of the School of Environmental Sciences at the University of Hull and Pete Rowley of the School of Earth Sciences at the University of Bristol, said: “Ultimately, the Hunga volcano will be a vital case study for better understanding the risk that undersea and shallow-water volcanoes pose to the submarine environment and critical seafloor infrastructure.”
Image: The island of Hunga Tonga-Hunga Ha’apai destroyed by the volcanic eruption in January 2022 leaving two small remnant islands. Credit: Contains modified Copernicus Sentinel data 2022, CC BY-SA 3.0 IGO <https://creativecommons.org/licenses/by-sa/3.0/igo/deed.en>, via Wikimedia Commons
