Magazine article Science News

Dueling Theories on Dune Fields: C-Shaped Sand Mounds Persist by Colliding or Calving

Magazine article Science News

Dueling Theories on Dune Fields: C-Shaped Sand Mounds Persist by Colliding or Calving

Article excerpt

No sand dune is an island. Interactions between crescent-shaped, or barchan, dunes stabilize the sand mounds and explain how vast swarms of them can persist over time, two new studies find. But the studies don't agree on what kind of interactions matter: One team argues that dunes colliding and breaking apart keeps fields from growing into giant sand piles, while the other claims that dunes calving off each other is the key.

Even if they disagree, "both papers are providing convincing evidence that the generation of small dunes in a field is a very important ingredient to explain the structure of barchan corridors," says Eric Parteli of the University of Erlangen-Nuremberg in Germany.

Barchans arise in deserts where the ground is hard and flat and strong winds blow sand in one direction. Thousands of the dunes can occupy a narrow strip. Fueled by wind, the dunes travel at different paces and can traverse up to 100 meters in a year.

Scientists have struggled to explain what maintains these assemblages. "It's unclear why barchan dunes exist at all," says Pieter Vermeesch, a geologist at University College London. Tiny dunes should shrink and disappear while big ones should grow infinitely large.

Mathieu Genois of Paris Diderot University and colleagues say collisions prevent dunes from growing out of control. If two barchan dunes collide, they can merge into one crescent or they can split up into multiple smaller barchans. …

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