New study finds that the fastest ever underwater flow was triggered by 2022 Tonga eruption

A new study, published on September 7 in the science magazine, showed that the eruption of the Hunga Tonga–Hunga Haʻapai submarine volcano in January 2022 caused the fastest underwater flow ever recorded.

Furthermore, the January 2022 eruption sent roughly six cubic kilometers of material flying into the atmosphere, and later collapsing on the sea floor, rolling down the submarine volcano’s 40-degree slopes.

As a result, chunks of the volcano were detached from the collisions and made the underwater debris flow denser. It is worth noting that roughly ten cubic kilometers of material were remobilized from the seafloor in the event, according to the research.

This flow of rock, ash and gas travelled a maximum distance of some 100 kilometers and destroyed a domestic and an international telecommunication underwater cable in its path. More specifically, these cables were located about 50 and 80 kilometers away from the volcano respectively, with the international one being in a seafloor valley, meaning that the debris flow had to travel uphill.

Monitoring the seabed, and after sampling and surveying the location, the researchers were able to identify the followed path and compare it with the cable brake timing. This way, they could specify that the flow reached maximum speeds of 73-122km/h (45-75mph) at the time it collided with the first cable, which was found buried some 30 meters under the debris.

As for the second collision, it was found that even after travelling a greater distance and even uphill, the flow was still moving at speeds of 47-51km/h (29-32mph).

Finally, while a great number of such volcanoes exist underwater, only a few of them are monitored. Dr Yeo of the National Oceanography Centre and member of the paper’s research team highlights how such events pose a great risk, that remains poorly understood, to coastal communities and critical infrastructure, and points out the need for more monitoring.