Tech

Tonga eruption is still revealing new volcanic hazards


It’s clear that Hunga involves an unusually explosive formula that may not be easy to replicate. In about a month, the eruption went as planned—moderately intense, gaseous and ash, but manageable. Then everything went sideways. That seems to be the result of at least two factors, Cronin says. One is a mix of magmatic sources of slightly different chemical composition underneath. When they interact, they produce gas, expanding the volume of magma within the confines of the rock. Under tremendous pressure, the rocks above began to crack, allowing cold seawater to seep in. “Sea water is seasoned, if you like,” says Cronin. A massive explosion followed—two of them, actually—flushing trillions of tons of material straight through the top of the crater, some seemingly into space.

Both of those explosions created large tsunamis. But the biggest wave followed—potentially caused, Cronin thought, by water flooding into a kilometer-deep hole suddenly dug out of the seabed. “It was something really new for us,” he said—a new type of threat to consider elsewhere. Previously, scientists thought that this type of volcano could only really create a large tsunami if one side of the crater collapsed. The bottom line, he said, is that subterranean volcanism is more diverse and in some cases potentially more extreme than anyone thought.

But the process of piecing together eruptions also highlights challenges in studying subterranean volcanism. A typical mapping expedition would include a large, fully crewed research vessel equipped with multi-beam sonar to map the seafloor for changes and a water sampling kit to look for chemical signatures of ongoing activity. But sailing through a potentially active caldera is risky—not because a volcano can erupt, but because gas bubbles can cause a ship to sink. In Tonga, the researchers solved that problem with smaller ships and an autonomous ship.

Even Tonga, which has been visited four times in the past year due to the influx of research funding to groups studying the eruption, is unlikely to receive another major crewed mission in the next few years. , Cronin said. The cost is just very high. It may take decades to survey each volcano in detail, even just those within the Tongan arc. This is a shame, says Walker, because such expeditions are one of the few ways that scientists get close enough to actually observe volcanic activity. An ideal scenario would involve more funding for such missions, as well as investments in improving new technology, such as autonomous ships, which can be difficult to operate in the open ocean. dangerously large.

Without them, scientists are stuck observing from a distance. This is difficult to do when you are trying to observe underwater events—but not impossible. Satellite technology can detect objects known as pumice rafts—volcanic rocks floating on water—as well as algal blooms, fed by minerals released by volcanoes. And USGS, like its partners in Australia, is in the process of installing a network of sensors around Tonga that can better detect volcanic activity, combining seismic stations with acoustic sensors and webcams to track active explosions. Keeping it up and running will be a challenge, Lowenstern says – it’s about keeping the system connected to data and power, and making sure Tonga can staff the facilities. He added that Tonga is just one of many Pacific countries that could use the help. But it was a start.

One of the benefits of studying the volcanoes of Hunga so closely that researchers have now identified new volcanic features of interest. Over the next few years, Cronin foresees a process of determining which volcanoes need more attention. On their final Hunga voyage in 2022, Cronin’s team used their time onboard to visit two other underground volcanoes in the area, including one about 100 miles to the north with The mesa-like terrain resembles that of Hunga before it erupted. The maps will form the basis for future surveys looking to get out of the water, a way for researchers to find out the level of activity going on beneath the sea and rocks. So far, Cronin reports, the ocean is calm.

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