Airguns gauge undersea volcanoes.

• Position: Geology

A mechanism that counters established thinking on how the rate at which tectonic plates separate along midocean ridges controls processes such as heat transfer in geologic materials, energy circulation, and even biological production has been revealed by a Georgia Institute of Technology, Atlanta, study. The research also has pioneered a new seismic technique--simultaneously shooting an array of 20 airguns to generate sound--for studying the Earth's mantle, the layer beneath the 10- to 40-kilometer-deep crust on the seafloor.

"Midocean ridges produce most of the volcanism on the Earth, releasing a lot of heat--in some places enough to support large biological communities on the seafloor," notes Daniel Lizarralde, assistant professor in the School of Earth and Atmospheric Sciences. "There are large variations in the amount of ridge volcanism worldwide that are probably controlled by processes deep in the mantle. Those processes leave behind an imprint in the crust and mantle that have moved away from ridge. In this study, we did something new. We went well away from ridge where things have cooled down and looked at those imprints."

Previous research has demonstrated that slow rates of plate separation, or spreading, correlate to dramatic changes in various processes occurring at midocean ridges. However, geologists have not had a thorough understanding of this cause and effect relationship. Hoping to reveal that connection, Lizarralde and his colleagues chose to study an extreme case that occurred over a 35,000,-000-year period along an 800-kilometer line southwest of Bermuda in the western Atlantic Ocean.

They found that, as the spreading rate changes, the ability...