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Tonga volcanic eruption confirmed as the largest explosion recorded since 1883

Scientists analysing data from the volcanic eruption found it was the largest explosion since 1883, and roughly comparable to the Krakatoa eruption in Indonesia that killed more than 30,000 people.

Scientists say the eruption of Tonga's Hunga Tonga-Hunga Ha'apai volcano was the largest explosion documented by researchers since 1883.

Key points:
  • An article published in Science found the Tonga volcanic eruption was comparable to the Krakatoa eruption
  • The Tonga explosion generated Lamb waves that travelled horizontally along Earth's surface for days
  • It also produced audible sounds that could be heard up to 10,000 kilometres away

Hunga Tonga-Hunga Ha'apai's eruption, which has been blamed for just six deaths, was similar in size to the Krakatoa explosion in Indonesia in 1883, according to the findings published in Science.

The Tonga explosion generated pressure waves, called Lamb waves, which travelled horizontally along Earth's surface for more than six days, according to the article.

Those Lamb waves are usually associated with large, atmospheric explosions, such as other volcanic eruptions and nuclear tests.

The Tonga volcanic eruption produced similar Lamb waves as the Krakatoa eruption that killed more than 30,000 people.

Scientists said nuclear explosions that have also created Lamb waves — such as the largest nuclear test in the USSR in 1961 — were of similar amplitude but lasted for a shorter period of time compared to large volcanic explosions such as the one in Tonga.

That's because volcanic explosions are much more complicated and not as pointed as nuclear explosions. 

January's eruption also produced audible sounds that could be heard up to 10,000 kilometres away in Alaska and generated infrasound — sound that can't be heard by humans — that echoed around the world.

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Satellite images show the size of the volcanic eruption

Professor Corentin Caudron — who co-authored the article — told the ABC that researchers had used more than 3,000 sensors and instruments around the globe, commonly used to detect earthquakes and tsunamis, to arrive at their findings.

"What we did, essentially, was to compare what we extracted, in terms of information, about all these waves that propagated around the globe, [and] compare that eruption with others that occurred in the past," Professor Caudron said. 

He said that, while instruments used in 1883 were of a lower resolution than those used now, they detected the same thing. 

"It's probably one of the first times we can see a Lamb wave associated with a volcanic explosion, and Krakatoa also did the same thing … it's the first time we can see those Lamb waves in a very detailed way."

University of Melbourne volcanologist and adjunct associate professor Heather Handley said the article confirmed what was observed after the eruption. 

Dr Handley said the Tonga explosion highlighted how the international community needed to work together to be prepared for a potentially worse volcanic eruption.

"[Another eruption] will happen. The world will have to be prepared to work globally, together, to make sure that when that … size of an eruption occurs that we're ready and best prepared because it could affect global food supply, network chains, communication systems," Dr Handley said.

Fallout from Tonga eruption and tsunami continues
An aerial shot shows destroyed houses and buildings on a small strip of island in Tonga.An aerial shot shows destroyed houses and buildings on a small strip of island in Tonga.
Hundreds of buildings were damaged or destroyed by tsunami waves after the eruption.(Supplied: Australia Defence Force/Christopher Szumlanski)

January 15's explosion triggered a tsunami that destroyed large parts of Tonga and blanketed volcanic ash over the kingdom.

The Pacific Island nation was isolated from the rest of the world for more than a month when the eruption and tsunami cut the country's only undersea internet cable, leaving people overseas unable to contact family and friends in Tonga. 

Tsunami waves were observed across the Pacific and reportedly damaged docked boats in New Zealand and caused an oil spill in Peru which was declared an environmental emergency.

The World Bank estimated the damage bill from the disaster will cost Tonga more than $125 million — equivalent to approximately 20 per cent of its GDP. 

About 600 buildings across Tonga were damaged or destroyed by the tsunami — half of those homes — and an estimated 1,525 people were displaced. 

The tsunami brought the most devastation to the country's tourism sector because it damaged resorts and natural attractions, while the agricultural sector was heavily impacted by volcanic ash.

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