Sand ripple shape? The shadow knows.
Trying to understand how trillions of grains are shaped into a sand dune is no easy task (SN:5/3/86, p.282). One step toward that end is described in the September GEOLOGY by Bradley T. Werner at Caltech in Pasadena and his colleagues. They report on a simple but accurate method for measuring the cross-sectional shapes of sand ripples, which play an important role in theories of the formation of sand dunes.
According to Werner's group, other researchers have devised a variety of techniques for measuring ripple size and shape, including impregnating sand ripples with a hardening solution so that they can be taken back to the laboratory and using three-dimensional photography to study the formation of sand ripples in wind tunnels. "... [A]lthough all these techniques produce useful information, they place a strain on the patience of the investigator," write the researchers. So they invented a method that is easy to use in the field and is accurate to within one sand grain. Werner's group photographs the shadow falling from a straightedge suspended over the ripples. From the shadow outline, they obtain a profile of the ripples. The next step, they say, is to make shadow movies of the ripples as they form.
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|Title Annotation:||accurate method for measuring cross-section shapes of sand ripples|
|Date:||Oct 18, 1986|
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