It is evident that Hunga contained an especially explosive recipe that is probably not easy to recreate. For a couple of month, the eruption proceeded as expected – moderately violent, with gas and ash, but manageable. Then all the pieces turned sideways. This appears to be the results of no less than two aspects, says Cronin. One was the blending of magma sources with barely different chemical compositions downstream. As these interacted, they produced gases, increasing the quantity of magma inside the rock boundaries. Under tremendous pressure, the rocks above began to crack, allowing the cold seawater to seep in. “The seawater added extra spice in case you like,” says Cronin. There was an enormous explosion – actually two of them – that sent trillions of tons of fabric straight through the highest of the caldera, a few of which apparently made it into space.
Both of those explosions caused an important tsunami. But the most important wave got here later – possibly caused, Cronin believes, by water pouring right into a kilometer-deep hole dug suddenly into the seabed. “This is something really recent for us,” he says, “a recent sort of threat to contemplate elsewhere. Previously, scientists believed that this sort of volcano could only really trigger a big tsunami if the caldera wall collapsed. The bottom line, he says, is that underwater volcanoes are more diverse and in some cases more capable of maximum behavior than anyone thought.
But the strategy of combining eruptions has also highlighted the challenges of studying underwater volcanoes. A typical mapping expedition will include a big, fully-crewed research vessel equipped with multi-beam sonar that maps the seafloor for changes and a battery of water-sampling instruments that search for chemical signs of ongoing activity. But sailing a ship through a potentially lively caldera is dangerous – not a lot since the volcano could erupt, but because bursting gas bubbles could sink the ship. In Tonga, scientists solved this problem with smaller vessels and an autonomous vessel.
Cronin says even Tonga, which has been visited 4 times previously 12 months as a result of the influx of research funds to eruption study groups, is unlikely to get one other major crewed mission in the following few years. The cost is just high. It would probably take a long time to review each volcano intimately, even just those within the Tongan arc. It’s a shame, says Walker, because these sorts of expeditions are considered one of the few ways scientists get close enough to see how volcanoes behave. The ideal scenario would involve more funding for these missions, in addition to investment in improving recent technologies, comparable to autonomous ships that will be difficult to operate within the treacherous open ocean.
Without them, scientists are stuck watching from a distance. It’s hard to do while you’re trying to look at underwater events, but it surely’s not inconceivable. Satellite technology can detect objects often known as pumice rafts – sheets of buoyant volcanic rock that bob on the surface of the water – in addition to algae blooms which might be nurtured by minerals released by volcanoes. And the USGS, like its counterparts in Australia, is within the strategy of installing a network of sensors around Tonga that may higher detect volcanic activity by linking seismic stations with sound sensors and webcams that look ahead to lively eruptions. Ensuring it really works will likely be a challenge, says Lowenstern – a matter of keeping the systems connected to data and power sources, and ensuring Tonga can handle the facilities. He adds that Tonga is just considered one of many Pacific countries that might use help. But that is the start.
One of the advantages of studying Hunga Volcano so thoroughly is that scientists have now identified recent volcanic features to look at out for. Over the following few years, Cronin anticipates a strategy of determining which volcanoes need more attention. On Hung’s final voyage in 2022, Cronin’s team used the ship’s time to go to two other underwater volcanoes in the world, including one about 100 miles north with a mesa-like topography that resembles Hunga before it erupted. The maps will provide a benchmark for future research that manages to get out onto the water, allowing scientists to learn the way much motion is occurring beneath the ocean and rocks. So far, Cronin reports, the ocean is calm.