James' World 2

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

Which is why, when researchers started scouring the ocean floor immediately surrounding the volcano, they expected to find a gnarly landscape. Surely it would be reshaped by the blast and littered with debris. Scientists believe that the explosion was the result of an incendiary recipe: hot, gaseous magma meeting cold, salty seawater. But how exactly did those two ingredients come together with such force? Some of the leading theories centered on the idea of a landslide or other collapse of the volcano’s slopes that helped water intrude into the magma chamber. That would also help explain the tsunami that killed three people on nearby Tongan islands. A massive shift in submarine rock also means displacing a massive amount of water.

A team of scientists from New Zealand’s National Institute of Water and Atmospheric Research, or NIWA, recently observed something different. Using ship-mounted acoustic instruments to map the seafloor, they found the terrain has indeed changed—it’s now covered with at least enough ash to fill 3 million Olympic swimming pools. But apart from that, it’s not all that different. The slopes of the underwater volcano are still largely as they were before the eruption; the same features still contour the surrounding seafloor. Within 15 kilometers of the volcano, some of those features are even still teeming with life, with starfish and corals clinging to rocky seamounts. “The first thing we did was a circle around the volcano, and I’m going, ‘What the hell?’” recalls Kevin Mackay, a marine geologist at NIWA who led the expedition. “It just defied expectations.”

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Photograph: Maxar/Getty Images

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