Why Was the Tonga Eruption So Massive? Scientists Have New Clues


How great was the January eruption of the Hunga-Tonga volcano? Four months of intensive science have only increased the scale. You could point out the audible booms that disrupted the night in Alaska, 6,000 miles away. Or perhaps the tsunamis in the Caribbean, created by a rare form of acoustic wave that jumped over the continents and shook the seas. In space, weather has also changed, NASA scientists said earlier this month, with blast winds accelerating to 450 miles per hour as they left the outer layers of the atmosphere. . This briefly redirected the flow of electrons around the planet’s equator, a phenomenon that had previously been observed during geomagnetic storms caused by the solar wind.

That’s why, when researchers began scouring the ocean floor immediately surrounding the volcano, they hoped to find a tumultuous landscape. It would probably be remodeled by the explosion and full of rubble. Scientists believe the explosion was the result of an incendiary recipe: hot, gaseous magma gathered from cold, salty seawater. But how exactly did these two ingredients come together so strongly? Some of the main theories focused on the idea of ​​a landslide or other collapse of the volcanic slopes that helped the water enter the magma chamber. This would also help explain the tsunami that killed three people in the nearby Tongues. A massive change in the underwater rock also means moving a massive amount of water.

A team of scientists from the National Water and Atmospheric Research Institute of New Zealand, or NIWA, recently observed something different. Using ship-mounted acoustic instruments to map the seabed, they found that the terrain has changed, it is now covered with at least enough ash to fill 3 million Olympic-sized swimming pools. But other than that, it’s not that different. The slopes of the submarine volcano are still largely as before the eruption; the same features still surround the surrounding seabed. At 15 kilometers from the volcano, some of these features are still full of life, with starfish and corals clinging to the rocky underwater mountains. “The first thing we did was a circle around the volcano, and I said,‘ What the hell? ’” Recalls Kevin Mackay, a NIWA marine geologist who led the expedition. “It just defied expectations.”

An area where they did not venture was just above the caldera, the depression he left behind when the volcano flew. Mackay’s large research ship, full of scientists and crew, had not dared to sail there, not because of the risk of big explosions, but because of the small eruptions of gas that could rise from the site of the eruption. “These gas bubbles can lower ships, and they’ve done it before,” he says. But they suspected total destruction. The islands that had come out of the sea just before the eruption had been broken by the explosion, suggesting a crater beneath the surface.

A day after the NIWA team published their findings, a second group of researchers from Tonga’s geological services and the University of Auckland helped fill out the map. Using a smaller boat that was less at risk from bubbles, the equipment came out of the boiler with a similar set of acoustic instruments. Yes, it was a hole. The section is 4 kilometers wide and 850 meters deep, and surprisingly limited, surrounded by the original slopes of the volcano. “What we have here now is a very large, very deep hole in the ground,” Shane Cronin, a volcanologist at the University of Auckland, told a news conference in Tonga. “It helps us understand why the explosion was so, so big.”

Both sets of observations are helping scientists reconstruct a massive underwater explosion unlike any they may have studied before. The image reveals that Hunga appears to have exploded directly. As the boiler broke in the early stages of the eruption, this probably introduced a flood of seawater that encountered deep regions of magma, causing a chain reaction. More sea water, more magma, more explosions.



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