The underwater Tongan volcano emitted the biggest atmospheric explosion recorded on Earth in more than 100 years, and Niwa researchers have discovered that almost 10 cubic km of the seafloor around it was displaced — the equivalent of 2.6 million olympic-sized swimming pools.
Project leader and Niwa marine geologist Kevin Mackay said two-thirds of the material came from the summit and the rest from the surrounding flanks.
Three-quarters of this material was deposited within 20km of the volcano, but almost 3.2 cubic km was still unaccounted for.
He said the missing debris could be partly explained by aerial loss.
"The eruption reached record heights, being the first we’ve ever seen to break through into the mesosphere. It was like a shotgun blast directly into the sky.
"The volume of this shotgun plume is estimated to be 1.9cubic km of material, which has been circulating in our atmosphere for months, causing the stunning sunsets we saw following the eruption.
"This goes some way to explaining why we’re not seeing it all on the seafloor," he said.
Despite the huge displacement of material, the volcano’s flank remained surprisingly intact.
However, the crater was now 700m deeper than before the eruption.
Niwa collected 150 sediment cores which were sent to the University of Otago and the National Oceanographic Centre in the United Kingdom for analysis.
The samples showed pyroclastic deposits (made up of dense lava, volcanic ash, and gases) were found more than 80km away from the volcano.
Niwa natural hazards principal scientist Dr Emily Lane believed they were what caused both the domestic and international communications cables to break.
"The sheer force of the pyroclastic flows is astonishing.
"We saw deposits in valleys beyond the volcano, which is where the international cable lies, meaning they had enough power to flow uphill over huge ridges and then back down again."
Mr Mackay said it was the first time scientists had observed underwater pyroclastic flows of this magnitude.
Dr Lane said these types of volcanos were found all over the world and it was important to know what had happened and why the eruption was so violent.
"The pressure anomaly generated by this eruption supercharged the tsunami so that it was able to travel right across the Pacific and worldwide.
"This mechanism meant that it could travel further and faster than our warning systems expected."
The research made it clear that underwater volcanic eruptions had serious implications for coastal communities around the world and further understanding of the risks from underwater volcanos was needed so we can better prepare and protect future generations and their ecological environments.
