Gear's loss is a gain for science
The destruction of seismic equipment points to a Pacific sea floor eruption
THE LOSS of earthquake-measuring instruments at an underwater volcanic mount off Mexico turned out to be a lucky break for scientists: It indicated an eruption and evidence of a new sea floor.
University of Hawaii oceanographer James Cowen and other scientists in May confirmed the seismometers had been atop the East Pacific Rise, which erupted and engulfed eight of the 12 instruments.
Cowen and colleagues from UH and other research facilities rushed to the site on the Scripps Institution ship New Horizon and lowered a camera on a sled. They were able to closely record a series of micro-earthquakes -- for the first time ever -- associated with the formation of a new sea floor.
Scientists aboard a research ship gathered around a water-sampling instrument package that they used during their mission to study water-column properties for evidence of hydrothermal discharge associated with the undersea eruption at the East Pacific Rise, off the coast of Mexico. Standing from left are Eric Simms (Scripps Institution), Cyrus Khambatta (UH), Alexander Treusch (OSU), Chad Holmes (Lamont Doherty Geological Observatory), Andrew Boal (UH), James Cowen (UH), Dale Hebel (UH) and Robert Polamares (Scripps). Sitting are Brian Glazer (UH), left, and Brooke Love (University of Washington). CLICK FOR LARGE
A preliminary report on data from the seismometers was released Thursday on the Science Express Web site and will appear in an upcoming issue of the journal Science.
The East Pacific Rise is one of three active sea-floor spreading centers designated by the National Science Foundation's Ridge 2000 program to document formation of the Earth's crust as it is happening and study the geology, chemistry and biology.
In 2003, Maya Tolstoy, marine geophysicist at the Lamont-Doherty Earth Observatory, placed a dozen ocean-bottom seismometers along part of the ocean mount.
In April, a ship returned to recover the 12 instruments but was able to collect only four. Measurements by the scientists indicated a volcanic eruption had recently occurred. The April expedition was "serendipitous," Cowen said.
Tolstoy said in a news release that seismic activity had built up at the site gradually for at least two years, leading to the eruption and raising the possibility that future eruptions might be forecast a year or more in advance.
With the seismometers right on the sea floor when the eruption occurred, they provided a lot of information about the character of the seismicity, the specific type of earthquakes, the source of the magma and how it moved through fissures in the ocean crust toward the surface, Cowen said.
"What is exciting is now wherever we have similar instrumentation on the sea floor and monitor that, we'll be in a much better position to forecast likely places where new eruptions will take place."
Tolstoy stressed the importance of real-time monitoring of the sea floor. "That way we can really begin to understand this fundamental building block of our planet, from the mantle to the microbe," she said.
Others from UH on the "rapid response" expedition were Brian Glazer and Andrew Boal, then both postdoctoral students at the NASA Astrobiology Institute, Dale Hebel, specialist in the oceanography department, and Cyrus Khambatta, graduate student in Cowen's lab on a fellowship from NASA.
Geochemist Ken Rubin, also of the UH School of Ocean and Earth Science and Technology, and other scientists followed Cowen's expedition using Woods Hole Oceanographic Institution's ship Atlantis and manned submersible Alvin.
Rubin was among senior scientists diving on the new East Pacific Rise lavas in the Alvin. "It was very fascinating," he said.
The deep-tow camera from Woods Hole Oceanographic Institution was used to scan sections of the East Pacific Rise.
Rubin has been analyzing rocks collected from that and earlier expeditions to the midocean ridge. He uses different dating methods for different time scales, "from last month to about 500,000 years." His lab is the only one in the world capable of dating young lava rocks, using a short-lived radioactive isotope.
One of the most interesting things about the site, the UH scientists said, is that it is the only place where two eruptions have been documented at the same place in the ridge system.
The first one, in 1991, was detected accidentally by a group of people diving in the Alvin, Rubin said. "They got down to the seabed and saw something no one had seen before" and pieced it together that an eruption had occurred, he said.
Since then, he said, the site has been under "intense study" by scientists of all disciplines, studying large-scale processes and organisms and how the system responds.
Through the seismic record, Tolstoy "was able to see a signature of events building up to the eruption," Rubin said.
In addition, scientists diving in the Alvin were able to make a series of measurements about how far the lava went and changes in topography to the ridge crest system, he said.
"All of that will tell us about the mechanics of the eruption and, coupled with dating, will tell us how long the event took. We were never able to do this before."
Cowen, who is studying the water chemistry and other aspects of the sea floor eruption, said, "To understand how these midocean ridge volcanic events occur and what leads up to them, and what's the aftermath of them, is to understand the fundamental process on Earth."