Record-breaking Tonga volcano sheds new light on how underwater volcanoes blow

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Oddities and quarks7:09 p.m.The consequences of a record volcano: Hunga Tonga–Hunga Haʻapai two years later

It was a record-breaking explosion that swept the world – repeatedly, as it turns out.

Just over two years ago, the most powerful underwater volcano on record erupted off the coast of the small island nation of Tonga in the Pacific Ocean, about 2,000 kilometers from New Zealand .

Kevin Mackaymarine geologist at New Zealand’s National Institute of Water and Atmospheric Research, spoke with Oddities and quarks” the host, Bob McDonald, about this volcano with its record explosion.

What did the volcano look like in the “before” photo?

It is 2.5 kilometers high and approximately 30 kilometers in diameter. It would be very impressive if you saw it on land, but underwater it is just one of tens of thousands of very similar features underwater. It is a classic volcanic cone with a very flat top about four kilometers wide and a slight crater at the top.

Now take me back to that day in 2022 when the volcano erupted. What was it like for you in New Zealand?

It was around 6 p.m. on a summer evening. I was mowing the lawn and heard what I thought was artillery fire. I thought “that’s strange”, because it’s not the Queen’s birthday or anything special.

It wasn’t until I spoke to the media that I realized what I had actually heard was the supersonic boom of this massive explosion. It turned out that this volcano produced the most powerful sound ever recorded in human existence.

Watch: Tonga volcano of 2022 sent shockwaves around the world

So how far away was the sound of the eruption heard or felt?

This shot was heard audibly in Alaska, 11,000 kilometers away. It’s just crazy. And the detonation itself is actually a blast wave so powerful that you can see it from satellites beaming across the world. And we know from weather stations that he went around the world three times.

Wow. So once you started investigating this topic, what were you hoping to find when you went to the site?

Our initial hypothesis was that this volcano erupted like a terrestrial volcano. When a volcano explodes, like that of Mount Saint Helena, it literally shatters.

So when we mapped this mountain after the eruption, we expected to find that much of the mountain was gone.

The first thing we saw that surprised us was the still intact mountain. The difference is that there is now a huge hole at the top, almost a kilometer deep.

Two images of the volcano are side by side, with the darker blue color showing deeper depths and the green and white color showing shallower depths.  The left front image has a flat top while the right image has a large hole.
Underwater mapping images show the Hunga Tonga-Hunga Ha’apai volcano at different depths before the 2022 eruption, on the left, and after, on the right. The eruption left a huge hole at its summit. (Hélène Le Mevel/Science/NOAA)

OK, what about the surrounding area?

When we put the cameras up we just saw devastation – not a little life to be seen. This is the most biologically productive part of the planet and we saw hour after hour, kilometer after kilometer, no life.

How much actual matter came out of the volcano?

We estimate about six cubic kilometers. This represents a large amount of material. When Mount St. Helena erupted in 1980, there was about a cubic kilometer of material.

There were six that went into the atmosphere, and then what goes up must come down, so that’s six cubic kilometers that came crashing back through the water onto the seafloor. He then removed an additional four cubic kilometers of material.

As a result, you now have 10 cubic kilometers of mobilized material. And like it moves through the water, it simply smothered the ocean floor in all directions.

A piece of equipment is lowered to the seabed where there are no signs of life.
In May 2022, scientists studying the volcano’s aftereffects lowered an imaging system through the clear water to thick, dense black smoke that obscured their visibility. (Rebekah Parsons-King/NIWA-Nippon Foundation/TESMaP)

How high in the atmosphere did the eruption occur?

The eruption itself broke many records in our understanding of science. When a very large volcano erupts, its clouds usually rise about 25 kilometers high, and when the ash hits the bottom of the stratosphere, the jet stream pushes this material away and sort of rolls it up. around the world.

This particular eruption was so powerful that NASA detected the cloud rising up to 57 kilometers high. This is twice as high as the previous known limit of a volcanic eruption. This meant that it had so much power and speed that it crossed the jet stream of the stratosphere and pushed ash and essentially salt water into the mesosphere.

NASA has detected water from the Pacific Ocean in space. No one even thought this was possible because of gravity.

A black-and-white satellite image shows the volcano's mushroom cloud, center left, and a plume of steam and smoke rising toward the satellite, on the right side of the image.
A white plume rises above Tonga as the Hunga Tonga-Hunga Ha’apai underwater volcano erupts. (NOAA/ACEI/Reuters)

So what do you know now about what triggered such a massive explosion?

This type of eruption would never occur on earth. Atmospheric air is not dense enough to create this level of explosion. This explosion can only occur in an underwater environment, because when water meets magma, it instantly turns into steam. And the steam will be 1,000 times what it was in the water.

So you have cubic kilometers of seawater hitting a magma chamber that instantly causes it to reach 1,000 times its volume. That’s it.

This particular rash is a bit like a “Goldilocks” rash. If a volcano had been shallower, there would not be enough volume of salt water to create this level of explosion. But if the volcano had been deeper, then the water pressure would be too great to allow this explosion to occur. The water pressure would have suppressed this explosion.

Boy. So it was essentially a steam explosion that gave him this violence, but what was the initial trigger?

There was a pool of magma in the magma chamber that had been there for about five years. There was a new pulse of rich, volatile magma being pushed into the magma chamber. And this volatile, rich magma (was like) shaking a bottle of champagne. And it’s what motivated this explosion.

There was an explosion that removed part of the lid of the magma chamber which let in some more water. It exploded. This freed up the roof of the magma chamber a little more to let in more water. And there was this chain reaction where every little eruption let in a little more water. Eventually, the entire magma chamber was exposed to all the seawater, and that was it.

The workers stand among a tangle of trees and trash that have become mixed up in the volcano's aftermath.
This photo taken on January 16, 2022 shows a search and rescue team surveying tsunami damage in Haatafu, on the west coast of Tonga’s main island Tongatapu, after the January 15 eruption. (Matangi Tonga/Pesi Fonua/AFP/Getty Image)

It was indeed a very large volcano with a lot of local destruction, but it didn’t have the kind of global impact that a volcano like Krakatoa had in terms of climate change.

This (Tonga Volcano 2022) changed the climate. Currently, the climate is still changed because of this. Krakatoa crashed on earth, so the mechanism isn’t quite the same.

When a volcano erupts over water, a lot of ash is released into the atmosphere. This creates a barrier that prevents solar radiation from reaching the Earth’s surface, creating global cooling.

This particular volcano, because it was underwater, what was being pushed into the atmosphere was mostly steam. And H2O vapor is the most powerful greenhouse gas there is. So it warmed the planet because there was so much water being pushed into the mesosphere, something like 60 million Olympic swimming pools filled with water from the Pacific Ocean.

This (also) affected the pattern of the jet stream. And the net result is that in the Northern Hemisphere last summer, your crazy summer, (with) the heat waves and the huge bushfires in Canada, this volcano made it even worse.


The questions and answers have been edited for length and clarity.

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