On land, a volcanic eruption is dramatic—columns of ash, fountains of lava, a complete remaking of the terrain.
But terrestrial eruptions make up only a fraction of Earth’s volcanic activity. The rest occur underwater, particularly along the hidden, 40,000-mile-long network of volcanoes in which Earth’s crust is spreading apart and producing new rock along its mid-ocean ridges. That means a huge number of eruptions happen mostly out of sight. “We never know when it’s happening, even though it’s probably happening all the time,” says Bill Chadwick, a volcanologist at Oregon State University. “The ocean hides everything.”
Scientists have recently gotten a rare glimpse of this underwater action: a secret submarine eruption has made its presence known in the Bismarck Sea near Papua New Guinea. The first hint came from a small swarm of earthquakes on May 8, with NASA satellites spotting steamy volcanic plumes and discolored water the next day. By early June satellite images showed that brownish-gray streaks—rafts of volcanic material called pumice—had begun to surround the Admiralty Islands, pointing to an eruption potentially located along the Titan Ridge, a volcanic area that last saw an eruption in 1972.
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“We have so few observations of these submarine eruptions that every time we get a chance to study one, we know we’re going to make incredible progress in our understanding,” says Adam Soule, a submarine volcanologist at the University of Rhode Island.
Pumice rafts spotted near Papua New Guinea’s Admiralty Islands.
NASA Earth Observatory/Lauren Dauphin
The pumice—“frothy rock,” as Chadwick describes it—forms when gas-rich molten rock suddenly cools. It is one of only a handful of flags to underwater volcanic activity. If the magma contains enough gas and the eruption is shallow enough, this pumice can float up to the ocean surface, where it can linger for years, either in the water or washed up on beaches. (Less gas or more water above a volcano means pumice isn’t able to reach the surface before it becomes waterlogged and sinks.)
The new eruption has been somewhat difficult for scientists to pinpoint because it’s in “a really complicated tectonic setting” where plate boundaries and their movement is confusingly jumbled, says Julie Bowles, a geophysicist at the University of Wisconsin–Milwaukee.
Fortunately, Chadwick says, scientists were recently able to map the area, giving researchers a baseline to compare with once they’re able to survey the scene after the eruption ends. “Almost certainly there’ve been huge changes,” he says. “Maybe there’s a big new cone that wasn’t there before or a big new crater. Who knows?”
If scientists are able to compare the seafloor before and after the eruption, they’re likely to see a host of changes, such as both sunken pumice and lava features, which underwater often take a form called pillow basalts. These are “rounded, bulbous forms that you basically never see on land,” Bowles says. They develop their characteristic shape as seawater quickly quenches the blobs of lava spewing forth. And of course, anything living on the site has likely been wiped out by the neighborhood cataclysm. Scientists will also be able to use satellite observations of the pumice rafts to hone estimates of the size of the eruption.
All told, that makes the eruption a remarkable scientific opportunity for those focused on submarine volcanism. “There’s so much discovery remaining to be made,” Soule says. “We’ve barely scratched the surface.”
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