Scientists Lose Instruments, Gain Look at Seafloor Formation

How much is too much to pay for a priceless set of seismic data? That is a question geophysicists from Scripps Institution of Oceanography at UC San Diego and other institutions are pondering as they consider the fate of ocean-bottom seismometers stuck on the Pacific Ocean seafloor off Mexico. The scientists have discovered the instruments were buried by lava following a volcanic eruption that took place along the East Pacific Rise in January 2006.

For three years, researchers associated with the National Science Foundation's Ridge 2000 program, a long-term study of mid-ocean ridges, have been measuring seismic activity at the site by sinking seismometers to the seafloor and subsequently retrieving them. Twelve seismometers were initially deployed in 2003, but only four were retrieved in April of this year during a research cruise aboard the R/V Knorr, led by Alberto Saal and Don Forsyth of Brown University. Three more of the seismometers responded electronically to the command to release and rise to the sea surface, but never did so. The rest remained silent. Maya Tolstoy, a geophysicist at Lamont-Doherty Earth Observatory at Columbia University and former Scripps doctoral student, suspected a possible eruption but more evidence was required to be certain.

The Ridge 2000 Program office at Scripps worked closely with the National Science Foundation and Ridge researchers to mount two response cruises to the area. The first response cruise, led by James Cowen of the University of Hawaii on Scripps' research vessel New Horizon in early May, lowered a camera that confirmed what the scientists suspected. Their instruments had been directly on top of a section of the East Pacific Rise that erupted. A second response cruise led by Karen Von Damm of the University of New Hampshire on R/V Atlantis located some of the seismometers and confirmed that they were trapped in fresh lava flows.

Instead of bemoaning their fate, the group celebrated their fortune-no one has ever closely recorded the series of micro-earthquakes associated with the formation of new seafloor. Preliminary analysis of their data appears in an upcoming issue of the journal Science and will be released on the Science Express Web site November 23.

Tolstoy found that the frequency of seismic activity at the site gradually increased for at least two years leading up to the brief January eruption that entombed the instruments, raising the possibility that future eruptions may be forecast a year or more in advance.

"It's amazing that we know so little about something so fundamental to the planet," said Tolstoy. "Even if we don't get the rest of the instruments back we'll have learned quite a bit."

Now researchers are considering making another attempt to recover the seismometers in 2007 with a remotely operated vehicle. Scripps geophysicist Jeff Babcock, who manages the ocean bottom seismometer facility, said the replacement cost of the instruments is less than the cost of trying to salvage the lost eight, but that like a treasured photo album, they have another kind of worth.
"The data on there could be very valuable and that's the driving force," he said.

Ridge 2000 was formed in 2001 as an interdisciplinary, nation-wide program to study the geology, chemistry and biology of the poorly understood process by which Earth's crust is formed at oceanic spreading centers. The program is headquartered at Scripps on the campus of UC San Diego.
"Discovering new lava so soon after a seafloor eruption is a unique opportunity," said Donna Blackman, Scripps scientist and current chair of Ridge 2000. "It allows Ridge researchers a rare chance to see how geologic processes affect the deep-sea ecosystems that thrive near hydrothermal vents."

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About Ridge 2000: Ridge 2000 is a multidisciplinary science research program focused on integrated geological and biological studies of the Earth-encircling mid-ocean ridge system and funded by the National Science Foundation. See www.ridge2000.org.

Maps, photographs, visualizations and additional information about this project can be found on the Web at:
http://www.ridge2000.org/science/tcs/epr_2006_science_supp_material.php