Scientists in Oregon and Washington say an underwater observatory is yielding new insights into an undersea volcano erupting off the West Coast of the U.S.

The submarine eruption of the Axial Seamount, a mountain rising 3,000 feet above the sea floor around 300 miles off the coast, was first suspected after large changes in the seafloor elevation and a swarm of tiny earthquakes were detected late last month.

Researchers have been making observations of the Axial Seamount for 15 years, recording tiny movements of the ocean floor as magma inflates the volcano.

"It's kind of like a balloon — as magma is going into the balloon, it's inflating, and it pushes the seafloor up," says geologist Bill Chadwick of Oregon State University. "As more and more magma gets in, the pressure builds. Eventually, it reaches some critical pressure where [the seamount] can't hold it in anymore, and then it squirts out."

The researchers have been able to monitor the latest eruption in real-time using instruments on the seafloor connected to the shore by fiber optic cables.

Scientists at the University of Washington installed the system, known as the Ocean Observatories Initiative, last summer as the culmination of years of work.

"This is the first time we've done this," says UW Professor John Delaney. "We are right at the beginning."

The system includes eight seismometers placed around the edge of the large caldera of the Axial Seamount and sensors to record changes in water pressure as the mount's surface inflates or deflates, moving up or down.

"If the seafloor is going up, there's less ocean above you, so there's a little less pressure," Chadwick says. "It's not much, but our instruments are so sensitive [that] we can measure to within a millimeter of vertical motion."

Last week, the volcano's crater dropped around 6 feet in just 12 hours, while the number of earthquakes increased from hundreds a day to thousands, all recorded by the UW instruments.

"This is the first place in the world where we have a wired volcano on the seafloor," says Chadwick.

The fiber optic system can do more than just monitor the volcano, Delaney says, and could someday be used to track whale migrations, monitor fish populations and even measure ocean acidification caused by climate change.

"All those things are available to be studied using this fiber, which essentially allows you to be there without being there," Delaney says.

The system was built using funding from the National Science Foundation.

TAG volcano, Geology

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