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Barchans on Mars

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Barchan Dune in Namibia Image Credit: Wikimedia Commons

Barchan Dune in Namibia Image Credit: Wikimedia Commons

Sand dunes are basically mobile piles of millions of tiny bits of rock, sculpted by the wind into fantastic shapes. One of the coolest shapes is today’s weekly geology word, barchan. The Encyclopedia Britannica has the following definition:

barchan: also spelled Barkhan,  crescent-shaped sand dune produced by the action of wind predominately from one direction. One of the commonest types of dunes, it occurs in sandy deserts all over the world. Barchans are convex facing the wind, with the horns of the crescent pointing downwind and marking the lateral advancement of the sand. These dunes are markedly asymmetrical in cross section, with a gentle slope facing toward the wind and a much steeper slope, known as the slip face, facing away from the wind. Barchans may be 9–30 m (30–100 feet) high and 370 m (1,214 feet) wide at the base measured perpendicular to the wind. They gradually migrate with the wind as a result of erosion on the windward side and deposition on the leeward side. The rate of migration ranges from about a metre to a hundred metres per year. Barchans usually occur as groups of isolated dunes and may form chains that extend across a plain in the direction of the prevailing wind.

A handy illustration of a barchan dune Image Credit: wikimedia commons

A handy illustration of a barchan dune Image Credit: wikimedia commons

How cool is that? Giant crescent-shaped dunes moving slowly across a desert or plain, pushed along by near-constant wind. Or, you know, across the surface of other planets. Barchans have been photographed making their way across the surface of Mars, with their distinctive crescent shape visible from space. Martian barchans. Awesome.

Barchan Dunes on Mars Image Credit: NASA HiRISE

Barchan Dunes on Mars Image Credit: NASA HiRISE