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Deep-sea octopus
A deep-sea octopus explores the brand-new lava flows that erupted at Axial Seamount in 2015. At the time, this was probably the youngest seafloor on the planet. (NOAA / Oregon State University Photo / Bill Chadwick)

An underwater seismic network pioneered by the University of Washington and other institutions is revealing how thousands of tiny shocks can herald huge eruptions.

Results from the Ocean Observatories Initiative’s Cabled Array, published today by the journal Science and Geophysical Research Letters, focus on the buildup of seismic activity in advance of a 2015 eruption at Axial Seamount, the most active submarine volcano in the northeast Pacific Ocean. The release of the results was timed to coincide with this week’s American Geophysical Union meeting in San Francisco.

“Instruments used by Ocean Observatories Initiative scientists are giving us new opportunities to understand the inner workings of this volcano, and of the mechanisms that trigger volcanic eruptions in many environments,” Rick Murray, director of the National Science Foundation’s Division of Ocean Sciences, said in a news release. “The information will help us predict the behavior of active volcanoes around the globe.”

The NSF-funded Cabled Array is an underwater seismic monitoring network that was launched just months before Axial Seamount erupted in April 2015. The network sends data back via fiber-optic cables to give researchers a real-time picture of what’s going on a mile beneath the ocean’s surface, 250 miles off the Oregon coast. The University of Washington and Oregon State University are among the project’s partners.

“The new network allowed us to see in incredible detail where the faults are, and which were active during the eruption,” UW oceanographer William Wilcock, the lead author of one of the Science papers, said in a news release.

The readings helped researchers develop a map of Axial Seamount’s football-shaped magma reservoir beneath the seafloor. The core is composed of molten rock, surrounded by what Wilcock described as a “crystalline mush of partially molten rock.”

Before the eruption, the seafloor moved upward as molten rock built up in the reservoir. Measurements of seafloor vibrations and acoustic recordings showed a steady increase in tremors, from less than 500 per day to about 2,000 per day. The vibrations also showed strong tidal triggering, with six times as many earthquakes occurring during low tides than during high tides as the eruption neared.

During the eruption, the earthquake count went to 600 per hour. Lava streamed out from cracks in the caldera, causing the seafloor to drop by more than 8 feet. As time went on, the eruption morphed from a purely effusive outflow to a more explosive event, NOAA’s Robert Dziak.

Seismic station on seafloor
The long black cylinder at right is a seismometer installed atop Axial Seamount. The green plate processes real-time seismic data and sends it back to shore via the orange cable for the National Science Foundation’s Ocean Observatories Initiative. (UW / OOI-NSF / CSSF-ROPOS Photo)

The lava kept flowing throughout the month of May 2015. Then the flow, and the seismic activity, tailed off. The earthquake count dropped to just 20 per day.

“The volcano works like a balloon, inflating with molten rock between eruptions, and then quickly deflating as the volcano erupts,” said Scott Nooner, a geologist at the University of North Carolina at Wilmington.

Scientists say it’s easier to study volcanoes undersea because Earth’s crust is much thinner in the oceans than it is on land. “Axial Seamount is a great natural laboratory for learning about volcanic eruptions,” Oregon State University’s Bill Chadwick said. “It has a simple structure, is frequently active, but it doesn’t pose a hazard to people.”

Axial Seamount typically erupts every decade or so, which means there’s a good chance scientists will have another opportunity to study an upswing in seismic activity. The observatory centered on the volcano is designed to operate for at least 25 years.

“The Cabled Array offers new opportunities to study volcanism and really learn how these systems work,” Wilcock said. “This is just the beginning.”

In addition to Wilcock and Dziak, authors of the Science paper titled “Seismic Constraints on Caldera Dynamics From the 2015 Axial Seamount Eruption” include Maya Tolstoy, Felix Waldhauser, Charles Garcia, Yen Joe Tan, DelWayne Bohnenstiehl, Jacqueline Caplan-Auerbach, Adrien Arnulf and M. Everett Mann.

The second Science paper, “Inflation-Predictable Behavior and Co-Eruption Deformation at Axial Seamount,” was written by Scott Nooner and Bill Chadwick.

The paper in Geophysical Research Letters, “Voluminous Eruption From a Zoned Magma Body After an Increase in Supply Rate at Axial Seamount,” was written by Chadwick and Nooner as well as J.B. Paduan, D.A. Clague, B.M. Dreyer, S.G. Merle, A.M. Bobbitt, D.W. Caress, B.T. Philip and D.S. Kelley.

You can catch live video from Axial Seamount every three hours via the Ocean Observatories Initiative website.

Axial Seamount
This depth map shows the raised outer edge of Axial Seamount’s central caldera in deep red. Lava from the 2015 eruption is outlined in green. Lava from a 2011 eruption is outlined in blue. (UW Center for Environmental Visualization / John Delaney)
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