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Where Continents Divide, and Rocks Rise from the Deep

Along the Woodlark Rift, a long break in the earth’s crust in eastern Papua New Guinea, continents are breaking apart, “like a snake opening its mouth.” Geologic processes that are still a mystery are actively stretching the crust and pushing huge masses of rock, formed under immense pressures as deep as 100 kilometers below, to the surface. Offshore, the ocean floor is spreading.

The setting offers a unique opportunity for scientists to study the powerful forces reshaping the surface of the earth, responsible for the movement of continents and creation of oceans.

Map shows locations of seismometers deployed to study movements of the earth around eastern Papua New Guinea.
Map shows locations of seismometers deployed to study movements of the earth around eastern Papua New Guinea. Image: CDPapua project.

“We don’t really understand how you take a continent and make an ocean,” said seismologist Geoffrey Abers of the Lamont-Doherty Earth Observatory, a member of the research team who presented a talk on their work at the American Geophysical Union’s fall conference in San Francisco Tuesday. Abers said the Woodlark Plate, north of Papua New Guinea, is slowly swinging away from the more southern Australian Plate, as if on a hinge – like the snake’s mouth.

“This is one of the few places where the act of a continent breaking into an ocean is happening right now,” Abers said. The upthrust of the rock masses is also happening relatively quickly, he said – from 10 to 20 kilometers every million years.

Abers and his colleagues traveled to the region beginning in March 2010 to study this phenomenon, using an array of 39 seismometers, including eight special instruments dropped to the sea floor, deployed among the D’Entrecastaux Islands and Papuan Peninsula. They traveled by boat and helicopter, navigating a roadless, mountainous terrain entangled with jungle to install the instruments, then returned earlier this year to retrieve them.

The instruments recorded thousands of small earthquakes – too slight to feel – that occur regularly in Papua New Guinea. Using this data, they hope to form a picture of the underlying geologic structures, to better understand the mechanisms that are reshaping the earth and thrusting those masses of rock up from 100 kilometers below. The earthquake patterns can also offer clues to where larger earthquakes might occur. Abers said they only recently assembled a database of the gathered information and are beginning to analyze it.

Abers is working with Lamont-Doherty scientists including James Gaherty, Roger Buck and Terry Plank, and a team from the University of Papua New Guinea. The work, funded by the U.S. National Science Foundation, is part of a larger international CDPapua program being done in collaboration with several other institutions.

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