Cruise to the Incipient Rift

Emily Klein 'Mows' the East Pacific to Reveal Secrets of Magma

by Monte Basgall

A contingent of scientists and students from the Division of Earth and Ocean Sciences in the Nicholas School spent August on a ship moving back and forth, lawn mower-like, over a long lava-emitting crack in the Pacific Ocean’s floor.

Led by geochemist Emily Klein, an associate professor of earth sciences at Duke, with Woods Hole Oceanographic Institution marine geologist Deborah Smith serving as co-principal investigator, the expedition thoroughly mapped the area’s underwater topography, extensively photographed the bottom geology, and brought up enough rock samples to harden the muscles of Klein’s predominantly-female scientific crew.

Voyaging on a Scripps Institution of Oceanography vessel, the 279-foot R/V Melville, they braved hurricane-infested waters en route from San Diego to a spot just north of the equator for the rare opportunity to catch a new geological feature in the act of formation.

Called the “Incipient Rift,” (abbreviated IR,) this feature is part of the restless process of Plate Tectonics that splits the Earth into slowly migrating plates separated by zones of stress. Along those zones, called mid-ocean ridges, new ocean floor is created to the accompaniment of earthquakes and volcanic eruptions.

The R/V Melville did its work off one of those ridges, called the East Pacific Rise, which separates the huge Pacific Plate to its west from several other plates to the east. Two of those eastern plates are separated by another crust- making ridge system that currently culminates just east of the East Pacific Rise in a deep canyon called Hess Deep.

Hess Deep was the target of another Duke-led geological expedition in 1999 on which Klein was a co-principal investigator (the Web site is accessible at www.nicholas.duke.edu/hessdeep/hessdeep.html). During a break in the Hess Deep schedule, that expedition repositioned about 30 miles northwest so Klein could get her first look at the IR, which appears to be a brand new mid-ocean ridge.

Located at depths between 2,800 and 3,500 meters below the surface (9,180-11,480 feet), the IR was discovered by other researchers in the 1980s. It is known to extend about 75 kilometers (46 miles) to the east from a spot on the East Pacific Rise. Its edges are believed to be spreading apart, as ocean ridges do, at a glacial pace ranging between 0 and 33 millimeters a year. It also is known to be emitting lava—making it another ocean crust maker, if only a baby version.

During her 1999 mini-visit to the IR, Klein used a primitive technique called wax coring to pull up samples of basaltic glass, a form lava can take when it erupts at a temperature of 1,800 degree Fahrenheit and suddenly solidifies on encountering near-freezing ocean floor seawater.

A scientist who specializes in the chemistry of rocks, she collected this glass with a procedure somewhat like using tape to pull lint from a wool overcoat. With wax coring, however, the “tape” was an especially sticky mixture of surfboard wax and petroleum jelly affixed to the bottom of an iron cylinder. The cylinder was bolted to a 100-pound steel weight, giving the combination enough momentum to smash into the ocean bottom like a battering ram.

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