NASA: Tonga blast was 10 megatons, more powerful than a nuclear bomb Researchers who have been studying the volcano since 2015 say it was likely caused by seawater flowing into a chamber filled with magma.

NASA scientists estimate Tonga blast at 10 megatons

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NASA scientists have put an estimate on the force of the volcanic eruption near Tonga over the weekend - 10 megatons. That's bigger than most modern nuclear weapons. As NPR's Geoff Brumfiel reports, researchers are starting to piece together what caused the explosion.

GEOFF BRUMFIEL, BYLINE: In 2015, an entirely new island rose from the Pacific Ocean. It was created by a powerful underwater volcano to the north of Tonga's main island. Jim Garvin is chief scientist at NASA's Goddard Space Flight Center. He says the process of growing the island created something else.

JIM GARVIN: It produces layers - we call them reservoirs - of liquid rock under a solid rock crust.

BRUMFIEL: That liquid rock, or magma, flowed through tubes and channels and vast underground caverns. In December of last year, a huge amount spewed towards the surface. The island expanded. But beneath the waves, Garvin believes something else was happening.

GARVIN: The plumbing system underwater changed.

BRUMFIEL: And then this past weekend, he thinks it changed again. Liquid seawater flowed suddenly and forcefully into the chambers filled with liquid magma.

GARVIN: When you put a ton of seawater into a cubic kilometer of liquid rock, things are going to get bad fast.

BRUMFIEL: A huge explosion.


BRUMFIEL: That's what one Twitter user recorded from an island in Fiji over 250 miles away, and the sound went a lot farther than that.

MICHAEL POLAND: People in Alaska heard it. So it was a humongous explosion, no doubt about that whatsoever.

BRUMFIEL: Michael Poland is a geophysicist with the U.S. Geological Survey. He says this may have been one of the loudest events on planet Earth in over a century, but the eruption itself wasn't all that big.

POLAND: The amount of magma that came out was relatively small, especially when you compare it to the size of the explosion that it created.

BRUMFIEL: To be clear, the explosion blew to bits the island that the volcano had made just a few years before. The tsunami and ash cloud that followed have done a huge amount of damage to Tonga, which is now in the midst of a massive humanitarian emergency.

But really big volcanic eruptions can change the climate of the entire Earth. Poland doesn't expect that to happen in this case. Nevertheless, he does think there will be a lot of interest in the blast. He says it could teach scientists more about what happens when Earth and sea collide.

Geoff Brumfiel, NPR News.


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