Sand dunes can ‘communicate’ with each other

Even though they are inanimate objects, sand dunes can ‘communicate’ with each other, researchers have found. A team from the University of Cambridge has found that as they move, sand dunes interact with and repel their downstream neighbours.

Sand dunes in Namib desert. Photo: Keith Hardy/Unsplash

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, 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.”

Most of the work in modelling the behaviour of sand dunes is done numerically, but Vriend and the members of her lab designed and constructed a unique experimental facility which enables them to observe their long-term behaviour.

Water-filled flumes are common tools for studying the movement of 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 have built a circular flume so that the dunes can be observed for hours as the flume rotates, while high-speed cameras allow them to track the flow of individual particles in the dunes.

The two dunes started with the same volume and in the same shape. As the flow began to move across the two dunes, they started moving. “Since we know that the speed of a dune is related to its height, we expected that the two dunes would move at the same speed,” said Vriend. “However, this is not what we observed.”

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 observed to be different: the flow is deflected by the front dune, generating ‘swirls’ on the back dune and pushing it away. “The front dune generates the turbulence pattern which we see on the back dune,” said Vriend. “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. (University of Cambridge)

YOU MAY ALSO LIKE

Cosmic Magnifying Glasses Find Dark Matter in Small Clumps

Using NASA's Hubble Space Telescope and a new observing technique, astronomers have found that dark matter forms much smaller clumps than previously known. This result confirms one of the fundamental predictions of the widely accepted "cold dark matter" theory.

Scientists design platform to conduct chemical analysis using a smartphone

Scientists from the multidisciplinary research group ECsens of the University of Granada (UGR) have developed and tested a new system that enables a large number of chemical analysis techniques to be performed in situ, using a smartphone.

Microbes reflect the health of coral reefs

More microbes found on healthier Cuban reefs than on human-impacted Florida reefs.

Connecting the prehistoric past to the global future

Ancient past as important as current climate and human impacts in explaining biodiversity patterns.

Following the lizard lung labyrinth

Some lizards have unique airflow pattern: hybrid of birds and mammals.

A new study highlights the importance of undertaking physical activity of moderate–vigorous intensity during the early weeks of pregnancy

Researchers at the University of Granada have analysed for the first time the link between sedentary time vs. objectively-measured physical activity levels and systemic concentrations of glycaemic, lipid, and inflammatory markers among pregnant women.