AT 500 metres tall, Earth’s largest sand dunes are already monsters – yet they are set to grow bigger as the world warms.
Giant sand dunes are thought to form when smaller dunes crash into each other and pile up. To investigate if anything limits their size, Bruno Andreotti at the Denis Diderot University, Paris, and colleagues calculated what the atmospheric flow looks like around giant dunes. They found that the thickness of the lowest layer of the atmosphere – the boundary layer – controls dune size, with a thicker layer leading to larger dunes (Nature, vol 457, p 1120).
“Once the dune becomes big enough to interact with the boundary layer it creates waves in the air. These waves feed back and interact with the sand below, keeping a lid on the dune size,” explains co-author Brad Murray of Duke University in Durham, North Carolina.
Warmer air increases the thickness of the boundary layer, which explains why Earth’s largest dunes are found inland, in the hottest part of the desert. It also suggests that if global warming heats the planet in the right place, then dunes could get bigger.
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