Just how big to be January eruption of the Hunga-Tonga . volcano? Four months of intensive scientific research only adds to the scale. You can point to sonic booms that disrupt the night in Alaska, 6,000 miles away. Or perhaps the Caribbean tsunami, created by a rare sound waveform Jump across continents and rock the seas. In space, the weather also changes, NASA scientists said earlier this month, with winds from the explosion accelerating to 450 miles per hour as they leave the outermost layers of the atmosphere. This briefly redirected the flow of electrons around the planet’s equator, a phenomenon previously observed in geomagnetic storms caused by the solar wind.
That’s why, when researchers begin scouring the ocean floor right around the volcano, they expect to find a wondrous landscape. Surely it will be reshaped by the explosion and scattered with debris. Scientists believe the explosion is the result of a burning formula: hot magma, gas encounter cold, salty sea water. But how exactly did those two components come together with such a force? Some of the leading theories focus on the idea that a landslide or other collapse of the volcano’s slopes helped water enter the magma chamber. That would also help explain the tsunami that killed three people on nearby Tongan islands. A large change in submarine rock also means displacement of large amounts 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 sonars to map the seafloor, they found the topography has really changed — it’s now covered with at least enough ash to fill 3 million Olympic swimming pools. But other than that, it’s not all different. The underwater volcanic slopes remain largely intact as they were before the eruption; Similar features still surround the surrounding seafloor. Within 15 kilometers of the volcano, some of those features are even teeming with life, with starfish and coral clinging to the rock formations. “The first thing we did was go around the volcano, and I would ask, ‘What the hell is that? ”” Kevin Mackay, a marine geologist at NIWA who led the expedition, recalled. “It just defies expectations.”
One area they didn’t venture into was right above the crater, the depression left behind when the volcano blew. Mackay’s large research vessel, full of scientists and crew, dared not set sail there — not because of the danger of a large explosion, but because Smaller burps may rise from the site of the eruption. “Those air bubbles can bring ships down, and they’ve done it before,” he said. But they doubt total destruction. The islands that jutted out of the sea just before the eruption were destroyed by the explosion, indicating a crater below the surface.
The day after the NIWA group publish their findings, a second team of researchers at the Tonga Geological Service and the University of Auckland helped fill out the map. Using a smaller vessel that poses less of a risk from bubbles, the team traversed the crater with a similar acoustic instrument set. Yes, it is a hole. The rift is 4 km wide and 850 meters deep, and is amazingly constrained, bounded by the original slopes. “What we have here now is a very big, very deep hole in the ground,” explained Shane Cronin, a volcanologist at the University of Auckland, at a news conference in Tonga. “It helps us understand why the explosion was so, so big.”
Two sets of observations are helping scientists reconstruct a massive underwater explosion unlike any they’ve been able to study before. The image shows that Hunga appears to have blown straight up. When the crater ruptured in the early stages of the eruption, this has the potential to create a flood of seawater that meets deep regions of the magma, triggering a chain reaction. More seawater, more magma, more explosions.
