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New Zealand; Pacific
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Press release: NIWA
Tonga eruption caused fastest ever underwater flow
The 2022 Tonga volcanic eruption triggered the fastest underwater flow ever recorded.
NIWA and the UK’s National Oceanography Centre (NOC) say that the flows travelled at speeds of up to 122km/hour – up to 50% faster than any other recorded.
This new analysis, made possible by the NIWA-Nippon Foundation Tonga Eruption Seabed Mapping Project (TESMaP), comes after earlier results showed the eruption of Hunga-Tonga Hunga-Ha’apai remobilised a staggering 10km3 of material from the seafloor.
As material from the volcanic eruption collapsed into the ocean, this triggered a huge surge of rock, ash, and gas that caused extensive damage to Tonga’s underwater telecommunication cables some 80km away.
Dr Emily Lane is NIWA’s Principal Scientist for Natural Hazards and is a co-author on the paper. She said the timings and locations of the damage to two subsea cables allowed them to determine the speeds of flows.
“Just a few months after the eruption, our team set sail to find out what caused it and what the impacts were. Surveys showed that Tonga’s domestic cable was buried under 30m of material, which we sampled and confirmed as containing deposits formed by a powerful seafloor flow triggered by the eruption.
“What’s impressive is that Tonga’s international cable lies in a seafloor valley south of the volcano, meaning the flow had enough power to go uphill over huge ridges, and then back down again,” said Dr Lane.
Kevin Mackay is a NIWA marine geologist and voyage leader of TESMaP. He says that this is just another record ticked off the list for this astonishing event.
“The seafloor flows were one of the big unknowns from this eruption – with it being an underwater volcano, it’s something you rarely get to study just after the fact. With atmospheric pressure waves circling the globe multiple times, and it being the largest atmospheric explosion on Earth in over 100 years, this just adds to that impressive list,” said Mr Mackay.
Dr Isobel Yeo is a volcanologist at the National Oceanography Centre (NOC) and joint-lead scientist on the paper. She said this work is helping us to better understand the hazards of submerged volcanoes worldwide.
“A huge number of the world’s volcanoes lie under the ocean, yet only a handful of those are monitored. As a result, the risk posed to coastal communities and critical infrastructure remains poorly understood, and more monitoring is urgently needed,” said Dr Yeo.
Dr Mike Clare a geohazards researcher, also at NOC, said “Findings from this important study not only improve our understanding of one of the largest events on our planet, but are already being used by the subsea cable industry to design more resilient communications networks in volcanically active regions. Subsea cables are a critical part of all of our lives, so making sure global connections stay secure is important”.
The paper was part of a joint international project including NIWA, The Nippon Foundation, and the Natural Environment Research Council in collaboration with 13 partners from Tonga, New Zealand, Australia, Germany, USA, and the UK.
Media contact: Jess Rowley, Jessica.Rowley@niwa.co.nz, +64 (0)27 839 0730
Press release: GNS
GNS co-authored paper captures destructive power of the 2022 Hunga Tonga-Hunga Ha’apai volcanic eruption.
An international research team, including researchers from GNS Science, has today released details of how the collapse of a major volcanic eruption column into the ocean severed international communications and triggered the fastest underwater flows ever recorded.
The massive eruption of the submerged Hunga Tonga-Hunga Ha’apai Volcano on 15 January 2022 triggered shockwaves that travelled around the planet and excavated a huge crater to 850 m below sea level.
The new research, published in Science, describes what happened below the surface of the sea when the column of erupted volcanic material collapsed and plunged straight back into the ocean. The sudden delivery of huge volumes of hot volcanic rocks, ash and gas into the ocean created avalanche-like flows, which travelled at speeds of up to 122 km/hour along the seafloor, causing extensive damage to the two seafloor cables that connected Tonga and its many islands to the global telecommunications network.
Scientists and industry collaborators undertook seafloor sampling and surveys in the immediate aftermath of the eruption, which showed that the subsea cable damage was caused by powerful and dense currents.
Researchers were able to determine the speeds of eruption-triggered seafloor flows for the first time and to better understand the hazards posed by other submerged volcanoes worldwide. The extremely fast flow speeds were caused by collapse of the 57 km high eruption plume when it fell directly into the ocean onto underwater flanks of the submerged volcano.
“The height from which the volcanic column collapsed, and the resulting speed and power of the submarine flows, explains the widespread damage to the seafloor cables” said Cornel de Ronde of GNS Science, a co-author on the paper.
“This research highlights that explosive eruptions from the many submerged volcanoes around New Zealand and Pacific Island nations, especially the shallow ones, could also produce high-energy submarine density currents and warrant attention as tsunamigenic hazards to vulnerable coastal communities and critical subsea infrastructure.”
In May 2024, GNS scientists will lead an international marine research voyage back to what is now known as Hunga volcano, to collect geological, geophysical and water column data inside the crater and over the flanks of this submerged eruption vent to better understand how the destructive 2022 eruption might have been triggered. The scientists hope to learn more about the processes that generate such powerful underwater volcanic driven flows and how they might be applicable to the numerous submarine volcanoes that sit within New Zealand’s maritime estate.
Media Contact: Nikki Hawkey, n.hawkey@gns.cri.nz, +64 (0)21 759257
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Shane Cronin, Professor of Volcanology at the University of Auckland
This research came about because submarine communication cables were destroyed by the Hunga eruption. We all rely on these for our data services and internet. When they broke during the eruption, the scientific community were immediately puzzled. They broke so soon after the eruption that we could not understand what could have done this.
“Tsunami is fast enough, but not possible, because the cables lie under several thousand m of sea water and tsunami only affect shallow areas. Ultimately we discovered that they were destroyed by gravity currents – that is, submarine landslide-like flows of volcanic rock and sand that travel along the ocean floor.
“Once we discovered why the cables were damaged, scientists were also puzzled as to how the submarine flows were so fast. Knowing the timing of eruption from seismic and infrasound signals and the timing of cable break via internet outage, the velocity of these flows was astonishingly high – the fastest of any known past submarine flow ever.
“We think that the intense and rapid feeding of dense volcanic material from the Hunga eruption caused the extremely fast submarine sediment flows. This is because the eruption was not typical in its behaviour – instead of shooting fragmented volcanic particles high into the atmosphere, most of its ejected material (90% of it) surged outwards and downwards into the ocean. This was because the material was both very dense, and ejected out a ring of fractures and faults circling the upper volcano – rather than a single central explosion ‘vent.’
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