Damp sandcastles

China’s Badain Jaran desert, which covers more than 40,000 square kilometers, is home to some of the world’s tallest stationary dunes, seen here from the International Space Station. They can stand 500 meters tall and cast immense shadows. What keeps these piles of sand immobile despite arid, windy conditions is a previously unknown source of groundwater, says Ling Li, an environmental engineer at the University of Queensland in St. Lucia, Australia.

Image Analysis Laboratory/NASA Johnson Space Center

Analyses of the water suggest that it’s snowmelt that flows hundreds of kilometers through fractured rocks to reach the desert. The annual flow, estimated to be 0.5 cubic kilometer, could provide an alternative to a planned $500 million river-diversion project, Li and his colleagues say in the Nov. 25 Nature.

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