A South Pacific ridge bears Brown’s name

Brown researchers exploring the ocean's floor were the first to map the geological feature.

by Kate Bramson

As with other scientific discoveries, if you’re the first to discover or map a volcanic ridge, you get to name it. And that’s how the Brown Ridge in the South Pacific recently acquired its name. Last winter, researchers affiliated with Brown were the first to map the approximately 200-kilometer-long ridge that they’ve since named after the University.

Geological Sciences Professor Donald Forsyth is preparing to present information about the Brown Ridge and other volcanic ridges at the American Geophysical Union’s (AGU) Spring Meeting May 28-31.

A group of 18 scientists and technicians, including students from Forsyth’s graduate-level “Marine Geophysical Techniques” class, discovered the ridge while on a 46-day research cruise last November and December. Forsyth was the chief scientist on the cruise. Daniel Scheirer, a senior research associate in Brown’s geological sciences department, was a co-principal investigator in the project.

Four Brown graduate students and undergraduate student Karl Rittger were on the cruise. For his senior thesis, Rittger is analyzing some of the small earthquakes under one of the volcanoes the group studied.

A continuous set of volcanoes on the floor of the Pacific, the Brown Ridge is about 200 kilometers long and about 20 kilometers wide. It reaches heights of about 2 kilometers above the sea floor.

Situated 2,400 miles east of Tahiti and 3,200 miles south of Los Angeles, the ridge is about 900 miles north of Easter Island, which is the nearest piece of land. The researchers flew into Tahiti, where they embarked on their cruise to the study site, which took about 6.5 days. To get home, they traveled to Easter Island and flew from there.

At the AGU meeting, Forsyth will discuss results gathered from 26 ocean-bottom seismometers that were deployed and then retrieved during the cruise. The scientists redeployed 24 of the instruments in a new configuration to gather a full year of data on the earthquake and volcanic activity in the region.

“We’re trying to look at the structure of the earth’s mantle to figure out the geometry of the melting region, how deep it is, how wide the melting region is and what the pattern of the mantle flow is,” he said.

Building on the work done last semester, a spring semester class taught by Forsyth and Associate Professor of Geological Sciences Karen Fischer has further analyzed data gathered by the researchers on last year’s cruise. The “Earthquake Seismology” class comprises six graduate students and one undergraduate.

In November, Forsyth and several Brown graduate students will retrieve the seismometers from the South Pacific on a second cruise to the region.

While earlier satellite research showed that parts of the Brown Ridge existed, scientists didn’t know how continuous the ridge was until the cruise last winter, Forsyth said.

The Brown Ridge is one of a number of ridges that no one really understands, Forsyth said. Researchers on the cruise are testing various theories about the origins of the South Pacific ridges.

Forsyth said this particular research is driven by curiosity. Understanding this volcanic ridge won’t help scientists predict earthquakes, but such research does advance understanding about how the earth works.

“You can sometimes apply what you learn in one place to another place,” Forsyth said. “It’s not this particular volcano that we’re interested in. It’s the pattern of flow in the earth’s mantle, and this just happens to be one manifestation of that flow.”