A survey by New Zealand and UK vessels, which was led by New Zealand's National Institute for Water and Atmospheric Research (NIWA), has been completed following the eruption in January 2022.

Hunga-Tonga Hunga-Ha'apai (HTHH) explosion sent ash and water-vapour half-way into space, and generated tsunami waves across the globe.

NIWA reported that researchers have now fully mapped the area around the Pacific volcano, and discovered seafloor was eroded and sculpted by violent debris flows out to a distance of over 80km (50 miles).

The gathered data indicated that at least 9.5 cubic kilometres of material was displaced during the catastrophic event. Two-thirds of that was the ash and rock ejected out through the volcano’s opening, scientifically known as the caldera.

Marine geologist and Niwa project director, Dr Kevin Mackay said that the blast can be compared to a shotgun blast up into the sky, and some of that material went beyond the stratosphere into the mesosphere (57km in altitude).

He also added that this was the highest recorded eruption column in history.

Though there was a huge displacement of material, the volcano’s flank remained intact. However, the caldera, is now 700m deeper than before the eruption.

Further evidence from the research led NIWA to discover pyroclastic flows following the eruption, which are currents made up of dense lava, volcanic ash, and gases which can reach temperatures of 1,000°C and speeds of 700km/hr.

The survey work tracked flows that even managed to travel up and over elevations of several hundred metres, and the pyroclastic flows played a big part in the HTHH event. 

“This explains, for example, what caused both the domestic and international communications cables to break, with the domestic cable now being buried under 30m of eruptive material.”

NIWA also reported the dramatic effects caused to the ecosystems in the region, due to the significant reshaping of the seafloor. There was little sign of any animal life on the flanks of the volcano, in deeper water channels, and most of the surrounding seafloor.

However, there were patches of abundant life that had survived the eruption on several seamounts, giving hope for recovery.

Taaniela Kula from Tonga Geological Services said, “we’ve always underestimated submarine volcanoes, and that there are five additional just surrounding Tongatapu, so it is clear that there is a need for more and urgent planning.”

The survey was carried out by the Tonga Eruption Seabed Mapping Project (TESMaP) and New Zealand’s Research Vessel (RV) Tangaroa.

TESMaP was funded by the Nippon Foundation of Japan and organised with the help of Seabed2030, which is an international effort to properly chart Earth’s ocean floor.