Axial Seamount vent in ocean floor

A vent on Axial Seamount spews hot water and bits of microbial matter after a 2011 eruption.

Bill Chadwick, Oregon State University, Copyright Woods Hole Oceanographic Institution

Underwater network gives scientists a rare glimpse into deep-sea volcanoes

Most volcanic eruptions on Earth happen in a hidden, dark place: deep underwater. Scientists rarely detect these outbursts on the sea floor, but last year, they caught a seamount eruption in the act. Now, researchers have characterized it in unprecedented detail—showing how a rash of earthquakes preceded the eruption and how bulging of the volcano’s surface was used to successfully forecast the eruption. Scientists say the results will help them understand how other volcanoes around the world behave.

The eruption began on 24 April 2015 at Axial Seamount, which lies 480 kilometers off the Oregon coast. Researchers already had a good picture of the volcano’s magma chamber, and they’ve now learned how it erupts, thanks to a cabled array of seismometers and pressure gauges deployed by the U.S. Ocean Observatories Initiative (OOI) and other projects. Scientists hope the results, published today in two Science papers, will shed light on volcanic processes, and also help quiet the OOI’s detractors, who have criticized the project’s $1.8 billion lifetime cost.

Immediately after the OOI sensors came online in late 2014, they started recording hundreds of daily tremors, says William Wilcock, a marine geophysicist at the University of Washington in Seattle who led the first study. By March 2015, they had increased to upward of 2000 per day. The frequency of earthquakes also tracked the tides, with more than six times as many events occurring at low tide—a pattern that can be a sign of an imminent eruption, Wilcock says. If the volcano is close to erupting, pressure from the magma critically stresses the faults, so that a drop in water pressure at low tides can trigger small earthquakes. “You unclamp the faults,” he says. After the eruption, seismometers also recorded booms that the researchers attribute to steam exploding out of fresh rock, which helped them map lava flows.

The eruption didn’t come out of the blue, however. Scientists had some pressure recorders, which measure seafloor deformation, in place for eruptions in 1998 and 2011. Based on how fast magma seemed to be accumulating again in recent years, lifting the roof of the volcanic caldera, researchers were expecting another outburst soon. “The magma chamber inflates to a certain level, and then it can no longer withstand the pressure anymore and the magma breaks out,” says Scott Nooner, a geophysicist at the University of North Carolina in Wilmington.

In September 2014, after seeing that the caldera had started growing at a faster rate, Nooner and William Chadwick, a geologist at the Hatfield Marine Science Center in Newport, Oregon, predicted another eruption in 2015. In the second study, they show that their forecast was successful. The researchers also documented how the caldera deflated by 2.5 meters after the lava erupted.

At the moment, such forecasts are only possible for well-behaved volcanoes like Axial, Nooner says. “We think it’s a simpler volcanic system than a lot of volcanoes on land.” But Nooner thinks it’s a good start toward ultimately understanding more complicated volcanoes, like those along subduction zones that pose threats to people. Researchers have only monitored one other submarine volcano with seafloor seismometers, and this is the first one where they tracked seafloor deformation through several eruption cycles, he says.

Other researchers are equally excited. “That is really a great advance,” says Vera Schlindwein, a seismologist at the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany, who was not involved in the work. Such comprehensive measurements are rare for submarine eruptions, and although every volcano is different, Schlindwein says the results will help other researchers interpret sparser data from other locations. “With such full coverage, it helps to place these others in a better framework.”

Wilcock and others hope that the results will help demonstrate the value of the OOI, a network of 830 moored, mobile, and seafloor-based instruments at seven sites around the globe. A 2015 U.S. National Academies of Sciences, Engineering, and Medicine report suggested shrinking the costly project to fund other oceanographic research during a time of contracting budgets. The rollout has also been marred by delays and problems with data management and distribution. “On anything big and new, there’s always going to be people criticizing it,” Wilcock says. But he says the new results show how the program is already starting to pay off.

Nooner adds that the OOI’s ability to alert researchers to an eruption right when it happens lets them respond rapidly and make more measurements—for instance, of changes in water temperature and chemistry that can only be detected immediately after an eruption. The 2015 eruption provided proof of concept for real-time monitoring, he says, and next time Axial erupts, researchers hope to mount such a response. Given how the caldera is inflating now, Nooner thinks they won’t have to wait long. Based on his latest measurements, he predicts the seamount will blow again in just three short years.