Tonga volcano: 2022 Hunga-Tonga underwater eruption largest ever recorded - pyroclastic density currents

The January eruption of the Tonga volcano has been confirmed as the largest explosion ever recorded in the atmosphere by contemporary instruments.

The findings mean the blast was significantly larger than any volcanic erupiton of the 20th century, or any atomic bomb test undertaken after World War II.

When the underwater mountain erupted at the start of the year, it ejected ash and water vapour half way to space, causing tsunami waves to whip around the world.

Only the Krakatoa eruption in 1883 is likely to have rivalled the atmospheric disturbance produced in recetn history. People 10,000 kilometres away in Alaska reported hearing numerous booms.

Here is everything you need to know about it.

What has been learned?

The area around the Pacific volcano has been mapped by vessels from New Zealand and the UK, a research project led by the National Institute of Water and Atmospheric Research of New Zealand (Niwa).

The research has revealed that intense debris flows scraped and altered the ocean floors for more than 80 kilometres (50 miles) around the Hunga-Tonga Hunga-Haʻapai seamount.

According to data collected, at least 9.5 cubic kilometres of material were ejected during the cataclysmic event, the equivalent of around 4,000 Egyptian pyramids.

Two-thirds of that ash and rock was expelled from the volcano's caldera, or opening, while the last third was scraped from the top and sides of Hunga-Tonga as debris dropped back down to sweep across the ocean floor.

These flows are known as pyroclastic density currents, which are tumbling, “avalanches of scorching rock,” according to BBC Science Correspondent, Jonathan Amos. In water, the flows’ blistering heat would have encased them in a frictionless steam cushion, allowing them to “run and run” at breakneck speeds.

Niwa’s survey effort found evidence of debros flows that managed to move up and across elevations of several hundred metres, and can be blamed for the loss of the cable that connected Tonga to the world internet. Despite being 50 kilometres south of Hunga-Tonga and past a large hill on the seafloor, a major piece of this data link was cut.

“Where you had these flows, there is nothing living there today,” said marine geologist and Niwa project director Dr Kevin Mackay. “It’s like a desert 70km from the volcano. And yet, amazingly, just under the rim of the volcano, in places that avoided these density currents, you do find life. You find sponges. They dodged a bullet.”

How will the findings make a difference?

The results of the research will eventually be used in hazard mitigation, preparing Pacific nations located near the volcanic zone that stretches from New Zealand's North Island all the way to Samoa. From this research, they’ll better know where to build new infrastructure and how to safeguard it, as well as the magnitude of the risk they face.

“We’ve always underestimated submarine volcanoes,” said Taaniela Kula from Tonga Geological Services. “There are five additional just surrounding Tongatapu. It means we need more planning and urgent planning.”