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Don Turcotte: From convection to chaos

The first thing noticeable on walking into Don Turcotte's office at the University of California, Davis, is a long table strewn with papers and manuscripts in process, covered with edits and pasted corrections, plus a few textbooks. Two textbooks are by Turcotte: Geodynamics, with Gerald Schubert, and a volume Turcotte wrote on fractals and geophysics, the first defining textbook in the field. Floor-to-ceiling metal shelves hem in the work surface, filled with journals, some collected since the beginning of his almost half-century career, and the window on the far wall frames a winter view of a dry California valley, with a few pine trees stretching toward blue sky.

Don Turcotte, shown here in his office at the University of California at Davis, was awarded the American Geophysical Union’s Bowie Medal last December. Photo by Naomi Lubick.

Turcotte says he jettisoned a good third of his journals when he moved out from Ithaca, N.Y., just over a year ago. As a professor at Cornell University's geology department, Turcotte published his seminal work in geophysics, describing subduction and mantle convection. Now a recipient of the Bowie Medal, the American Geophysical Union's (AGU) top honor, Turcotte reflects on his path from aerospace engineering to geophysics.

While the then-engineer was on sabbatical at Oxford University in 1965, someone suggested he meet Ron Oxburgh, "this crazy geologist who thinks that the mantle might be convecting," he says. They met over dinner with sherry at the university's St. Edmunds Hall and talked about concepts that would set off the impending tectonic revolution. "I said, oh sure, it doesn't sound too complicated," Turcotte said. Working with Oxburgh (who is now a lord in the British Parliament), he shifted gears to geophysics. What Turcotte wrote that year was not published until 1967, and it turned out to be a landmark paper describing the physics of mantle convection, mountain building and rift zones.

In 1973, Turcotte moved from the Cornell engineering department to the geology department as it moved into the tectonic age. He became chair in the 1980s, while he "explored virtually every aspect of physical Earth geology," wrote former colleague Laurence M. Cathles, in a citation for the Bowie Medal, awarded at the AGU annual banquet last December. In addition to Turcotte's publications in planetary remote sensing and geophysics, Cathles counted over 150 papers on thermal subsidence in sedimentary basins and other fields.

Several years after writing Geodynamics, Turcotte switched gears once more, to fractals and chaos theory. His second landmark paper, on the power law of impacts, cratering and "interplanetary stuff," as he puts it, in the Journal of Geophysical Research in 1986, took several years to publish.

Turcotte says it's much harder to get his kind of nontraditional research published. Nevertheless, he now has a slew of citations in a variety of fields. "It's fine to dabble," Turcotte says, who sometimes never publishes a second paper in a field. "It's boring to stay in something."

In November, Turcotte was considering an invitation to a meeting this summer in Siena, Italy, asking him to speak on networks to a group of neurosurgeons. The impetus, he says, came from his paper on stream networks and their similarity to leaf veins, in the Journal of Theoretical Biology, one of the most cited of his biology papers.

Turcotte's interest in such a variety of problems is inspired by the challenge of answering new questions all the time, Schubert says. "To him, science is fun," he says.

Schubert, who was Turcotte's first master's student and later collaborator on two textbooks, says Turcotte is "truly exceptional in the way he does science." Schubert notes his generosity with ideas and his ability to get to the heart of things: "He has a very special talent to develop a simple explanation, simple (but quantitative) models, of very complex processes."

One example Schubert gives is Turcotte's controversial thesis of complete thermal instability on Venus: The planet's surface, according to Magellan's observations of meteor craters, was the same age everywhere. "Don thought about what could happen on Venus for this to occur," Schubert says, without plate tectonics or other ways of getting rid of the planet's core heat. Turcotte proposed the inside got so hot that it melted all at once, flooding the surface with lava in one giant turnover event. "Don developed some quantitative thermal history models to show Venus could in fact have evolved this way," Schubert says. "We don't know what truly happened, but it's considered plausible."

The idea of episodic subduction "came across as well as a lead balloon," Turcotte says. A mid-1990s BBC special focusing on Venus shows him obviously enjoying the controversy, which persists today.

Though Turcotte is now partially retired, he continues to work full-time at Davis, with a team that includes two Russian postdocs he brought with him from Cornell and fellow fractal geophysicist and modeler John Rundle. "I work seven days a week," Turcotte says.

Naomi Lubick

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