Tonga's volcanic eruption in 2022 caused fastest underwater flow ever recorded, scientists say

The 2022 volcanic eruption in Tonga caused the fastest-ever underwater flow recorded, scientists have found.

NIWA and the UK's National Oceanography Centre have said water flows around the Hunga Tonga Hunga-Ha'apai volcano reached speeds up to 122 km/h. That's 50 percent faster than any other recorded underwater flow.

Rock, ash, and gas spewing into Tonga's oceans damaged the Pacific nation's underwater telecommunications cables 80km away.

Dr Emily Lane, NIWA's natural hazards principal scientist, said the damage to the two subsea cables allowed scientists to estimate the flow speed.

"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," Dr Lane said.

She said the flow speed was impressive because Tonga's international cables lay in a seafloor abyss.

"Meaning the flow had enough power to go uphill over huge ridges, and then back down again," Dr Lane said.

NIWA marine geologist Kevin Mackay said it's another record broken.

"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," Mackay said.

Scientists didn't know much about the underwater flows after the eruption and they rarely get the chance to study them like this, Mackay said.

Dr Isobel Yeo, a volcanologist from the UK's National Oceanography Centre, said it's helping scientists understand the dangers of underwater volcanoes.

"A huge number of the world’s volcanoes lie under the ocean, yet only a handful of those are monitored," Dr Yeo said.

She said more monitoring is needed to help at-risk coastal communities.

Dr Mike Clare, also from the National Oceanography Centre, said subsea cables are critical for everyone.

The findings are "being used by the subsea cable industry to design more resilient communications networks in volcanically active regions," he added.

The research was part of a joint international project including NIWA, the Nippon Foundation, the NOC, and 13 other partners from six countries.

The new research comes after 2022 studies showed the eruption stirred up 10 cubic kilometres of seafloor material - the same as 2.5 million Olympic swimming pools.