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upstart writes in with an IRC submission for Bytram:

Sand dunes can 'communicate' with each other:

Using an experimental dune 'racetrack', the researchers observed that two identical dunes start out close together, but over time they get further and further apart. This interaction is controlled by turbulent swirls from the upstream dune, which push the downstream dune away. The results, reported in the journal Physical Review Letters, are key for the study of long-term dune migration, which threatens shipping channels, increases desertification, and can bury infrastructure such as highways.

When a pile of sand is exposed to wind or water flow, it forms a dune shape and starts moving downstream with the flow. Sand dunes, whether in deserts, on river bottoms or sea beds, rarely occur in isolation and instead usually appear in large groups, forming striking patterns known as dune fields or corridors.

It's well-known that active sand dunes migrate. Generally speaking, the speed of a dune is inverse to its size: smaller dunes move faster and larger dunes move slower. What hasn't been understood is if and how dunes within a field interact with each other.

"There are different theories on dune interaction: one is that dunes of different sizes will collide, and keep colliding, until they form one giant dune, although this phenomenon has not yet been observed in nature," said Karol Bacik, a PhD candidate in Cambridge's Department of Applied Mathematics and Theoretical Physics, and the paper's first author. "Another theory is that dunes might collide and exchange mass, sort of like billiard balls bouncing off one another, until they are the same size and move at the same speed, but we need to validate these theories experimentally."

Now, Bacik and his Cambridge colleagues have shown results that question these explanations. "We've discovered physics that hasn't been part of the model before," said Dr Nathalie Vriend, who led the research.

[...] The next step for the research is to find quantitative evidence of large-scale and complex dune migration in deserts, using observations and satellite images. By tracking clusters of dunes over long periods, we can observe whether measures to divert the migration of dunes are effective or not.

Journal Reference:

Karol A. Bacik, Sean Lovett, Colm-cille P. Caulfield, Nathalie M. Vriend. Wake Induced Long Range Repulsion of Aqueous Dunes. Physical Review Letters, 2020; 124 (5) DOI: 10.1103/PhysRevLett.124.054501

Original Submission