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Whipping up sand dunes from scratch

A theory describing how seasonal winds carve sandy terrain has aced a long-awaited experimental test.

In December 2007 a collaboration led by Zhibao Dong (Chinese Academy of Sciences) and Clément Narteau (Institute of Earth Physics of Paris and University Paris Diderot) flattened 40 acres of the Tengger desert in Inner Mongolia. For the next three and a half years, the researchers returned every few months to see how the region’s seasonal winds had shaped the local topography. By October 2011 the once-flat plot of land, outlined by the dashed curve in the figure, was striped with rows of dunes, roughly 4 m tall from peak to trough. The experiment was the first at-scale test of a decades-old theory describing dune evolution under shifting winds. Proposed in 1987 by David Rubin and Ralph Hunter, the theory posits that dunes orient in the direction that maximizes the sand transport normal to their crest lines. In the Tengger desert, where winds blow to the west in the summer and to the southeast in the winter, it predicts that dunes should align obliquely, at a roughly 50° angle, to the mean sand-transport direction. Indeed, that’s within a few degrees of the orientation Dong and company observed. Confident that the theory works, the researchers now aim to tackle the sand-dune problem in reverse—to develop strategies for inferring a region’s past wind activity from its current dune patterns. If successful, the approach could provide a way to deduce atmospheric circulation patterns on dune-rich Mars and Titan. (L. Ping et al., Nat. Geosci. 7, 99, 2014.)—Ashley G. Smart


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