Understandably, Hunga uses an unusually explosive recipe that is not easy to replicate. For about a month, the eruption proceeded as expected, moderately strong, with gas and ash, but manageable. Then everything went sideways. According to Cronin, this appears to be the result of at least two factors. One was the mixing of magma sources with slightly different chemistry below. When they interacted, they produced gases, expanding the volume of magma within the rock. Under the immense pressure, the rocks above began to crack, allowing cold sea water to seep in. “The seawater added an extra spiciness, if you will,” Cronin says. There was a massive explosion—two, actually—that ejected trillions of tons of material right over the top of the caldera, some of which appeared to have flown into space.
Both of these explosions caused large tsunamis. But the biggest wave came later – it was probably caused, according to Cronin, by water that swept a kilometer deep, suddenly dug out of the seabed. “This is something really new for us,” he says, “a new type of threat that should be considered elsewhere. Previously, scientists thought that such a volcano could really cause a strong tsunami only if the side of the caldera collapsed. The bottom line, he says, is that underwater volcanoes are more diverse and, in some cases, more capable of extreme behavior than anyone thought.
But the process of studying the eruption piece by piece also brought to the fore the problems of studying underwater volcanoes. A typical mapping expedition involves a large, fully crewed research vessel equipped with multibeam sonar that maps the seafloor for changes and a set of water sampling instruments that look for chemical signs of ongoing activity. But sailing a boat through a potentially active caldera is risky, not so much because the volcano could erupt, but because the rising gas bubbles could cause the ship to sink. In Tonga, researchers solved this problem with small ships and an autonomous vessel.
Even Tonga, which has been visited four times in the past year due to an influx of research funding into teams studying the eruption, is unlikely to get another big crewed mission in the next few years, Cronin said. Only the cost is so high. It will probably take decades to study every volcano in detail, even those in the Tongan arc. It’s a shame, Walker says, because these kinds of expeditions are one of the few ways scientists can get close enough to see how volcanoes behave. The ideal scenario would involve increased funding for these missions, as well as investment in improving new technologies such as autonomous ships, which can be difficult to operate in the treacherous open ocean.
Without them, scientists are stuck watching from a distance. This is difficult to do when you are trying to watch underwater events, but it is possible. Satellite technology can detect objects known as pumice rafts — sheets of floating volcanic rock that float on the surface of the water — as well as algae blooms that feed on minerals released by volcanoes. The USGS, as well as its counterparts in Australia, are in the process of installing a network of sensors around Tonga that can better detect volcanic activity by combining seismic stations with sound sensors and webcams that monitor active explosions. Keeping it running smoothly will be a challenge, Lowenstern said, a matter of connecting systems to data and power, and ensuring that Tonga can staff the facilities. He adds that Tonga is just one of many Pacific countries that may need help. But this is a start.
One of the benefits of studying Hunga Volcano so closely is that researchers have identified new volcanic features that should be looked at. Over the next few years, Cronin envisions a process of determining which volcanoes require more attention. On their last trip to Hungu in 2022, Cronin’s team used the ship’s time to visit two other underwater volcanoes in the area, including one about 100 miles to the north with a mesa-like topography that resembles Hungu before it. eruptions. The maps will form the basis for future exploration that manages to reach the water and allow researchers to figure out how much action is going on under water and rocks. For now, Cronin reports, the ocean is calm.