NASA scientists estimate Tonga blast yield at 10 megatons

(ORDO NEWS) — NASA researchers have estimated the power of a powerful volcanic eruption that occurred on Saturday near the island nation of Tonga. “We came up with a figure of about 10 megatons of TNT,” James Garvin, chief scientist at NASA’s Goddard Space Flight Center, told NPR.

This means that the force of the explosion was more than 500 times more powerful than the nuclear bomb dropped on Hiroshima, Japan, at the end of World War II.

According to Michael Poland, a geophysicist with the US Geological Survey, the explosion was heard far away in Alaska and was probably one of the most high-profile events that have occurred on Earth in the last century.

“This is possibly the loudest eruption since [the Indonesian volcano] Krakatoa in 1883,” says Poland. This powerful 19th century eruption killed thousands of people and threw out so much ash that most of the region was plunged into darkness.

NASA scientists estimate Tonga blast yield at 10 megatons 2

In the case of this latest development, Garvin says he believes the worst is over – at least for now.

“If past precedents for volcanic eruptions under such conditions are of any significance,” he added, “then we won’t get another such explosion for some time.”

Even three days after the explosion, Tonga remains largely cut off from the world. Submarine communication cables appear to have been cut and the airport covered in ash, preventing emergency flights from arriving in the capital, Nuku’alofa.

Reconnaissance flights by the New Zealand government showed that houses and many other structures were covered in ash. The New Zealand Foreign Office said two deaths had been confirmed and that the tsunami had inundated the west coast of the main island of Tongatapu, causing extensive damage.

The Tongan government reported another death and more damage on the outlying islands, including Mango Island, where all the houses were destroyed.

The volcano that caused the eruption was the subject of study by the NASA team for several years leading up to this explosive event. The islands that make up Tonga lie along a subduction zone, where one part of the Earth’s crust sinks under another, Garvin said.

“In this particular case, we don’t know when, it formed a kind of volcano with a big summit ring of hills and stuff,” says Garvin.

In late 2014 and early 2015, along the rim of this caldera, volcanic activity created a platform that rose from the sea to form a new island. Layers of steam and ash eventually connected this island, known as Hunga-Tonga-Hunga-Hapai, with two much older islands on either side of it.

Hunga-Tonga-Hunga-Hapai was completely destroyed by Saturday’s explosion, says Dan Slabek, a researcher at NASA’s Goddard Center and Science Systems and Applications Inc. Slayback says the explosion was so powerful that even the older islands nearby appear to be in pieces.

“It wasn’t ash – it was solid rock that had been blown to pieces,” he says. “It was amazing to see how it happened.”

Garvin says the formation of the island also likely contributed to its destruction. As it rose from the sea, layers of liquid magma filled the network of chambers below it. He suspects that the explosion was triggered by a sudden change in the underground plumbing, causing seawater to rush in.

“When you put a ton of sea water into a cubic kilometer of liquid rock, things get bad fast,” he says.

But for all its explosive force, the eruption itself was relatively small, according to Poland of the US Geological Survey.

Unlike the 1991 eruption of Mount Pinatubo, which spewed ash and smoke for several hours, the events at Hunga-Tonga-Hunga-Hapai lasted less than 60 minutes. He does not expect the eruption to cause any short-term changes in the Earth’s climate, as has happened in the past with other major eruptions.

The real mystery, Poland says, is how such a relatively small eruption could cause such a massive explosion and tsunami.

“It had a huge impact, far beyond what would be expected if it were completely above water,” he says. “That’s what’s haunting.”

Garvin says scientists want to do more research on the area around the volcano’s caldera. Analysis of satellite images is already underway, and drone flights may soon be added to it. He hopes the volcano will be safe enough for researchers to visit later in the year.

Poland says he is confident that researchers will learn much more in the coming days and months as they conduct new surveys of the area.

“It’s just a terrible event for the Tongans,” he says. But “it can become a standard, a turning point in volcanology.”

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