Undersea volcano gave off clear signals before erupting in 2011

Washington, Mon, 11 Jun 2012 ANI

Washington, June 11 (ANI): A team of scientists known for correctly forecasting the 2011 eruption of Axial Seamount years in advance, now insist 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 analysis using data from underwater hydrophones 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 in the future.

Based on the cyclic pattern of ground deformation measurements from bottom pressure recorders, they have further predicted that the Axial could erupt again, as soon as 2018.

Bill Chadwick, an Oregon State University geologist 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," Chadwick, who works out of Oregon State's Hatfield Marine Science Center in Newport, Ore, said.

"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," Chadwick said.

Bob Dziak, an Oregon State University marine geologist, had previously deployed hydrophones on Axial that monitor sound waves for seismic activity.

During a four-year period prior to 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 Nature Geoscience 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.

"Using seismic analysis, we were able to clearly see how the magma ascends within the volcano about two hours before the eruption," Dziak said.

"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."

The researchers also used a one-of-a-kind robotic submersible to bounce sound waves off the seafloor from an altitude of 50 meters, mapping the topography of Axial Seamount both before and after the 2011 eruption at a one-meter horizontal resolution. These before-and-after surveys allowed geologists to clearly distinguish the 2011 lava flows from the many previous flows in the area.

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," David Caress, an MBARI engineer and lead author on one of the Nature Geoscience articles, said.

"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," he said.

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

"Now that we know some of the long-term and short-term signals that precede eruptions at Axial, we can monitor the seamount for accelerated seismicity and inflation," OSU's Dziak said.

"The entire suite of instruments will be deployed as part of the Ocean Observatories Initiative in the next few years - including new sensors, samplers and cameras - and next time they will be able to catch the volcano in the act," Dziak said.

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," he added.

The research is being published this week in three separate articles in the journal Nature Geoscience. (ANI)



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