Tracing the evolution of a landscape

From above, parts of California's Southern Coast Ranges appear startlingly uniform: The landscape is composed of ridges and valleys that form a pattern of parallel lines as evenly spaced as teeth on a comb. "When you see such a regular pattern, it's like the landscape is screaming at you to figure out what's making it do that," says Taylor Perron, an associate professor of geology in MIT's Department of Earth, Atmospheric and Planetary Sciences (EAPS). The pattern is not unique to the California Coast Ranges; many landscapes around the world have evenly spaced valleys. In 2006, as a graduate student at the University of California at Berkeley, Perron hit upon a physical process to explain this striking feature of Earth's topography: The even spacing of valleys arose from competing forces of rivers eroding valleys and soil creeping downhill and filling them in. One force balances the other, keeping adjacent valleys from getting either too close or too far apart. As part of his PhD thesis, Perron worked his theory into a computational model to show how landscapes in the Coast Ranges and elsewhere might have morphed over millennia into their present-day forms. To see whether the model's results matched today's geomorphology, Perron made topographic measurements and calculated erosion rates at various sites.