ATLANTA -- Eberhard Bodenschatz watches 100 million years of geological time pass in an hour. He sees transform faults being created, rift valleys opening and spiral structures called microplates forming.
But the Cornell University physicist does not have an omnipotent view of the planet's ocean floor. Instead he is watching a model of tectonic evolution in a tub of molten wax. "These wax experiments," said Bodenschatz, "allow us to study millions of years of tectonic spreading in the laboratory. Remarkably, these phenomena appear to be similar to the Earth."
Bodenschatz, an associate professor of physics, presented the latest results from his wax modeling at the centennial meeting of the American Physical Society at the Georgia World Congress Center today (March 24).
His experiments, which build on research going back to the 1970s, examine phenomena similar to ocean floor spreading. His experimental apparatus, 3 feet long, 1 foot wide and 4 inches deep, is filled with molten wax. Cold air is blown over the wax surface so that a solid layer is formed.
The solid wax layer represents the Earth's cold and hard lithosphere, and the molten wax below, the Earth's plastic upper mantle. The solid layer of wax is divided, and the two halves are pulled apart with constant velocity. "This enables us to study the dynamical structure of the rift while wax constantly solidifies at the plate margins," Bodenschatz said.
For example, at very slow spreading rates, the rift remains straight with a deep valley, its lowest point at the rift axis. At medium rates the large-scale structure of the rift remains flat, interrupted by transform faults and curious structures called microplates. At fast rates the pattern is dominated by transform faults and fracture zones.
The microplates, formed at the intermediate rates, are of particular interest. They are tiny chunks of solid wax that appear at the rift and begin rolling up, something like a rolling snowball gathering snow. Each chunk of wax grows with constant velocity in the direction of the rift, slowing down the rotation rate and resulting in a spiral shape.
Microplates might be created in a similar fashion in the ocean floor. They are structures 100 to 200 kilometers across, the result of a chunk of the lithosphere being caught between two moving, overlapping plates. These ocean-floor microplates rotate by 18 degrees in about one million years, corresponding to just a minute in the wax tub. The best-known microplate is the Easter plate in the mid-Pacific.
How is the wax able to reproduce this ocean-floor phenomenon? "Well, nature does it," said Bodenschatz. "We are trying to find out why. The wax allows us easily to vary parameters and to study in detail the dynamics of rift formation."
Bodenschatz made it clear that his experiments are only a model for ocean-floor spreading and are not an exact replica. "The wax gives me a reasonable approach to model such processes in the Earth," he said. "I don't want to say I do the Earth. I do wax."
Contributing to the research were Cornell graduate student Rolf Ragnarsson and undergraduates William Bertsche, Richard Katz, Nate Gemelke and Jeron Carr. Bodenschatz is collaborating with Sarah Tebbens of the University of South Florida. The research is supported by the National Science Foundation Division of Materials Research and the Cornell Center for Materials Research.