Underwater ‘ears’ heard rumblings before 2011 undersea volcano eruption

by Mark Floyd, Oregon State University, 541-737-0788
Sources: Bill Chadwick, 541-867-0179; Bob Dziak, 541-867-0175; Dave Caress, 831-775-1775
NOAA media contact: John Ewald, 301-734-1165

A team of scientists that last year created waves by correctly forecasting the 2011 eruption of Axial Seamount years in advance now says that the undersea volcano located some 250 miles off the Oregon coast gave off clear signals hours before its impending eruption.

The researchers' documentation of inflation of the undersea volcano from gradual magma intrusion over a period of years led to the long-term eruption forecast. But new analyses using data from hydrophones -- underwater microphones that hear and record sounds underwater -- also show an abrupt spike in seismic energy about 2.6 hours before the eruption started, which the scientists say could lead to short-term forecasting of undersea volcanoes.

They also say that Axial could erupt again – as soon as 2018 – based on the cyclic pattern of ground deformation measurements from bottom pressure recorders.

Results of the research, which was funded by NOAA, the National Science Foundation, and the Monterey Bay Aquarium Research Institute (MBARI), were published June 10 in three articles in the journal Nature Geoscience. Some of the scientists are part of NOAA's Vents Program, which explores hydrothermal vents and underwater volcanoes.

Bill Chadwick, an Oregon State University geologist with the NOAA Cooperative Institute for Marine Resource Studies (CIMRS) and lead author on one of the papers, said the link between seismicity, seafloor deformation, and the intrusion of magma has never been demonstrated at a submarine volcano, and the multiple methods of observation provide fascinating new insights.

"Axial Seamount is unique in that it is one of the few places in the world where a long-term monitoring record exists at an undersea volcano – and we can now make sense of its patterns," said Chadwick, who works out of Oregon State’s Hatfield Marine Science Center in Newport, Ore. “We’ve been studying the site for years and the uplift of the seafloor has been gradual and steady beginning in about 2000, two years after it last erupted.

"But the rate of inflation from magma went from gradual to rapid about 4-5 months before the eruption. It expanded at roughly triple the rate, giving a clue that the next eruption was coming."

Bob Dziak, an Oregon State University marine geologist also with CIMRS, deployed hydrophones on Axial that monitor sound waves for seismic activity. During a four-year period before the 2011 eruption there was a gradual buildup in the number of small earthquakes (roughly magnitude 2.0), but little increase in the overall “seismic energy” resulting from those earthquakes.

That began to change a few hours before the April 6, 2011, eruption, said Dziak, who also is lead author on one of the articles.

“The hydrophones picked up the signal of literally thousands of small earthquakes within a few minutes, which we traced to magma rising from within the volcano and breaking through the crust,” Dziak said. “As the magma ascends, it forces its way through cracks and creates a burst of earthquake activity that intensifies as it gets closer to the surface.”

Dziak said that seismic analysis showed how the magma rose within the volcano about two hours before the eruption.

"Whether the seismic energy signal preceding the eruption is unique to Axial or may be replicated at other volcanoes isn’t yet clear – but it gives scientists an excellent base from which to begin," Dziak said.

The researchers also used a unique robotic submersible to bounce sound waves off the seafloor from an altitude of 50 meters (150 feet), mapping the topography of Axial Seamount both before and after the 2011 eruption. These before-and-after surveys allowed geologists to clearly distinguish the 2011 lava flows from many previous flows.

MBARI researchers used three kinds of sonar to map the seafloor around Axial, and the detailed images show lava flows as thin as eight inches, and as thick as 450 feet.

These autonomous underwater vehicle-generated maps allowed us, for the first time, to comprehensively map the thickness and extent of lava flows from a deep-ocean submarine in high resolution," said David Caress, an MBARI engineer and lead author on one of the articles. "These new observations allow us to unambiguously differentiate between old and new lava flows, locate fissures from which these flows emerged, and identify fine-scale features formed as the lava flowed and cooled."

The researchers also used shipboard sonar data to map a second, thicker lava flow about 30 kilometers (about 17 miles) south of the main flow – also a likely result of the 2011 eruption.

Table: Effects of ENSO and NAO on temperature and lake ice

Credit: Bai, X., J. Wang, C. Sellinger, A. Clites, and R. Assel, 2012. Interannual variability of Great Lakes ice cover and its relationship to NAO and ENSO. J. Geophys. Res, doi:10.1029/2010JC006932

Knowing the events leading up to the eruption – and the extent of the lava flows – is important because over the next few years researchers will install new instruments and underwater cables around Axial Seamount as part of the Ocean Observatories Initiative. These new instruments will greatly increase scientists' ability to monitor the ocean and seafloor off of the Pacific Northwest and perhaps, as Dziak said, "Next time be able to catch the volcano in the act."

The scientists also observed and documented newly formed hydrothermal vents with associated biological activity, Chadwick said.

"We saw snowblower vents that were spewing out nutrients so fast that the microbes were going crazy," he pointed out. "Combining these biological observations with our knowledge of the ground deformation, seismicity and lava distribution from the 2011 eruption will further help us connect underwater volcanic activity with the life it supports.”

Scientists from Columbia University, the University of Washington, North Carolina State University, and the University of California at Santa Cruz also participated in the project and were co-authors on the Nature Geoscience articles.

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Note to Journalists: This story can be complemented with several images, video clips and sound bites from the eruption and its aftermath.