Sand dunes 'talk to each other' as they creep across the desert

Rob Waugh
Contributor
Sand dunes actually communicate with each other (Getty)

It sounds like a fable from the Arabian Nights, but sand dunes actually whisper to each other - and slow down to move together.

Using high-speed cameras, scientists tracked sand dunes, and found that they seem to “communicate” through turbulence patterns.

Identical dunes thus start out close together but get further and further apart over time.

The study revealed front dunes generate a turbulence pattern, like a wake behind a boat, that affects its neighbour.

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The research is key for the study of long-term dune migration which threatens shipping channels, increases desertification and can bury roads.

Study author Karol Bacik, a Cambridge PhD candidate, said: "This interaction is controlled by turbulent swirls from the upstream dune, which push the downstream dune away."

Dune shapes are formed and start moving downstream when a pile of sand is exposed to wind or water flow.

Whether in deserts, on river bottoms or sea beds, sand dunes rarely occur in isolation and instead usually appear in large groups, forming striking patterns known as dune fields or corridors.

What has not been understood is if, and how, dunes interact with each other within a dune field.

Lead researcher Dr Nathalie Vriend said: "We've discovered physics that hasn't been part of the model before."

Dr Vriend and her lab team designed and constructed a unique experimental facility allowing them to observe the dunes' long-term behaviour.

Water-filled flumes are common tools for studying the shape-shifting sand dunes in a lab setting, but the dunes can only be observed until they reach the end of the tank.

Instead, the Cambridge researchers built a circular flume so that the dunes can be watched for hours as the flume rotates, while high-speed cameras allow them to track the flow of individual particles in the dunes.

Initially, the front dune moved faster than the back dune, but as the experiment continued, the front dune began to slow down, until the two dunes were moving at almost the same speed.

Crucially, the pattern of flow across the two dunes was found to be different.

The flow is deflected by the front dune, generating “swirls” on the back dune and pushing it away.

Dr Vriend said: "The front dune generates the turbulence pattern which we see on the back dune.

"The flow structure behind the front dune is like a wake behind a boat, and affects the properties of the next dune."

As the experiment continued, the dunes got further and further apart, until they form an equilibrium on opposite sides of the circular flume, remaining 180 degrees apart.

The findings were published in the journal Physical Review Letters.