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Researchers unveil secrets of undersea volcano

Two decades of consistent monitoring lead to insights, forecasts
December 15, 2016 New research on the eruption of an underwater volcano 300 miles off the coast of Oregon may help provide insights not only into the workings of submarine volcanoes, but to their land-based cousins, which pose a greater threat to people.
A deep-sea octopus explores the brand-new lava flows erupted at Axial Seamount in 2015. At the time, this was probably the youngest seafloor on the planet.

In September 2014, scientists from Oregon State University, NOAA’s Pacific Marine Environmental Laboratory, and University of North Carolina at Wilmington successfully forecastoffsite link the eruption of Axial Seamount, a submarine volcano, seven months in advance.

Now, two papers in Science and a paper in Geophysical Research Letters provide a window into the workings of these volcanic processes that are more difficult to study on land. The research was released today at the annual American Geophysical Union fall meeting in San Francisco.

“Axial Seamount is a great natural laboratory for learning about volcanic eruptions,” said William Chadwick, one of the lead authors from NOAA and Oregon State. “It has a simple structure, is frequently active, but it doesn’t pose a hazard to people.”

Three-time erupter

Axial Seamount, the most active submarine volcano in the northeast Pacific Ocean, has erupted at least three times, in 1998, 2011, and most recently in 2015.

Scientists were able to forecast the Axial Seamount eruption due to consistent monitoring for almost two decades. NOAA established the New Millennium Seafloor Observatory at Axial Seamount in 1996, and partners at the Monterey Bay Aquarium Research Institute joined the research effort in 2006. The National Science Foundation’s Ocean Observatories Initiativeoffsite link Cabled Array, launched in late 2014, has added a state-of-the-art seafloor observatory with monitoring instruments that provide real time, high resolution data transmitted by fiber optic cable.

Cross-sections along the east side of the Axial Seamount caldera. Grey areas are gradients of melt and mush zones within the magma reservoir. Orange lines show extent of 2011 dike. Red lines show initial dike intrusion from the high-melt zone of the magma reservoir feeding the 2015 eruptive fissures in the NE caldera.
Cross-sections along the east side of the Axial Seamount caldera. Grey areas are gradients of melt and mush zones within the magma reservoir. Orange lines show extent of 2011 dike. Red lines show initial dike intrusion from the high-melt zone of the magma reservoir feeding the 2015 eruptive fissures in the NE caldera. (NOAA)

“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,” said Rick Murray, director of the National Science Foundation’s Division of Ocean Sciences. “The information will help us predict the behavior of active volcanoes around the globe.”

Volcano inflates like a balloon

Precise pressure sensors at Axial measure vertical movements of the seafloor that take place as the volcano gradually inflates. “The volcano works like a balloon, inflating with molten rock between eruptions and then quickly deflating as the volcano erupts,” said Scott Nooner, an associate professor of geology at University of North Carolina.

During the 2015 eruption, instruments built by Oregon State and NOAA on the cabled array detected the seafloor rapidly dropping over eight feet.

“There is no substitute for having this level of detailed observations to advance the field,” said William Wilcock, a marine geophysicist at the University of Washington.

The precise measurements showed that the core of Axial’s football-shaped magma reservoir is made up of molten rock surrounded by what Wilcock describes as “a crystalline mush of partially molten rock.”

Steady increase of quakes

Measurements of vibrations of the ocean floor and acoustic recordings showed a steady increase of earthquakes before the eruption. Seismometers recorded the growth in frequency from less than 500 per day to about 2,000 per day, with 600 earthquakes per hour during the eruption.

Hydrophones recorded more frequent earthquakes two to three months leading up to the eruption with more than 50 earthquakes per day close to the event.

For the first time, using hydrophones on the cabled array, researchers were able to record a second phase of the eruption that was similar to fire-fountaining, ash-producing eruptions observed on land in Hawai'i. "These new observations suggest the volcano underwent a shift from purely effusive activity in the first week of the eruption, to more explosive activity as seismic activity waned,” said Robert Dziak, NOAA research oceanographer.

Read more about the Axial Seamount eruption hereoffsite link.

Read more on the Ocean Observatories Initiative here.offsite link

Oregon State University news release: http://bit.ly/2hOc6tf.offsite link

University of Washington news release: http://www.washington.edu/news/2016/12/15/offsite link

Contact:
Monica Allen, 202-379-6693 (cell - at AGU in San Francisco)