Tonga eruption displaced 10 cubic kms of sea floor
The Hunga-Tonga Hunga-Ha’apai volcanic eruption displaced almost 10 cubic kilometres of sea floor, the equivalent to 2.6 million Olympicsized swimming pools, a new study has found.
The underwater eruption on January 15 emitted the biggest atmospheric explosion recorded on earth in more than 100 years.
It destroyed everything in its path on the western part of Tonga’s Tongatapu and nearby islands. It also generated air pressure waves which went around the world.
Plumes from the volcano eruption generated the highest plumes of ash and water ever measured, penetrating the earth’s stratosphere.
Research led by New Zealand’s National Institute for Water and Atmospheric Research (NIWA) found that the displacement of sea floor was more than what was initially estimated.
It found that two thirds of it came from the summit and the rest from the surrounding flanks, and deposited material 20km from the volcano. Marine geologist and project lead, Kevin Mackay said almost 3.2 cubic kilometres of debris was still unaccounted for, possibly because of aerial loss.
‘‘This is why we didn’t notice the loss until we had mapped everything,’’ Mackay said.
‘‘The eruption reached record
heights, being the first we’ve seen to break through into the mesosphere. It was like a shotgun blast directly into the sky.’’
Mackay said the volume of the shotgun plume was estimated to be 1.9 cubic kilometre, which had been circulating in the atmosphere for months, causing stunning sunsets seen following the eruption. ‘‘This goes some way to explaining why we’re not seeing it all on the sea floor.’’
Mackay said despite the huge placement of material, the volcano’s flank remained intact, but the caldera, or crate, was now 700m deeper than before the eruption.
NIWA scientists also observed underwater pyroclastic flows – currents made up of dense lava, volcanic ash and gases that can reach temperatures of 1000 degrees Celsius and speeds of 700km/hour.
Principal scientist Dr Emily Lane said samples they collected were 80km away from the volcano, but it was the range they could survey.
‘‘The pyroclastic flows appear to extend beyond that distance, perhaps as far as 100km away,’’ she said. ‘‘They are also what caused both the domestic and international communications cables to break, with the domestic cable now buried under 30km of eruptive material.’’
Mackay said it was the first time scientists have observed underwater pyroclastic flows of this magnitude.