Despite the fact that sand dunes are inanimate objects, a new study published in the journal Physical Review Letters suggests that sand dunes can communicate with each other; as sand dunes move, they interact with one another.
In a surprising discovery, a group of researchers has discovered that “sand dunes” have the ability to “communicate with each other.”
Although sand dunes are inanimate objects, sand dunes can ‘communicate’ with each other. A Cambridge team discovered that as they move forward, sand dunes interact and repel their neighbors.
Using an experimental dune race track, the researchers observed that two identical dunes begin very close together, but over time they become separated more and more.
This strange yet surprising interaction is controlled by turbulent eddies of the dune uphill, which push the dune downhill.
The results, published in the journal Physical Review Letters, are key to the study of long-term dune migration, which threatens navigation channels, increases desertification and can bury infrastructures such as roads, highways and perhaps even buildings.
When a pile of sand is exposed to elements such as water flow or wind, it tends to form dunes and begins to move steeply with the flow. Sand dunes, whether those seen in deserts, at the bottom of the rivers or even on the seabed, rarely occur in isolation and. Researchers have found that generally, the sand dunes appear in large groups, forming striking patterns known as dune fields or corridors.
Scientists were already familiar with the fact that active sand dunes migrate. The speed of a dune is inverse to its size: smaller sand dunes tend to move faster and larger dunes move more slowly. What has not been understood by experts is whether the dunes within a certain field are able to 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,” explained Karol Bacik, a Ph.D. candidate in Cambridge’s Department of Applied Mathematics and Theoretical Physics, and the paper’s first author.
However, the researchers note that another possibility is that sand dunes actually collide and exchange mass.
“It’s kind 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.”
However, the new research points otherwise; Bacik and his colleagues have shown results that challenge these explanations. “We have discovered physics that had never been part of the model before,” said Dr. Nathalie Vriend, a researcher who led the research, in a statement.
The biggest challenge experts were faced with was modeling the behavior of the sand dunes numerically. However, Vriend and the members of his laboratory designed and built a unique experimental facility that allows them to observe their long-term behavior.
Water filled canals are common tools for investigating the flow of sand dunes in a laboratory. However, these sand dunes can only be observed until they reach the end of the track. To further study sand dunes, Cambridge researchers have created a circular channel so that the dunes can be observed for hours while the channel rotates, and high-speed chambers allow them to track the flow of individual particles in the dunes, allowing experts to study sand dunes in an unprecedented way.
The researchers explained that initially, they did not intend to study the interaction between two dunes:
“Originally, I put several dunes in the tank just to speed up the collection of data, but we didn’t expect to see how they started interacting with each other.” the researchers revealed.
The two dunes started with the same volume and in the same way. When the flow began to move through the two dunes, they started to move.
“As we know that the speed of a dune is related to its height, we expected the two dunes to move at the same speed,” said Vriend, who works at the BP Institute for Multiphasic Flow.
“However, this is not what we observe.”
The research found that the frontmost dune moved faster than the dune located at the back. However, to the surprise of experts, as the experiment continues, the front dune eventually slowed down, until both dunes mere moving at a newly identical pace.
The scientists were surprised when the pattern of flow across the two dunes was found to be different. The researchers explain that the flow is deflected by the front dune, generating swirls on the back dune, causing it to push 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,” Vriend added.
Eventually, and as the experiment moved forward, both sand dunes got further and further apart, until they created an equilibrium on opposite sides of the circular flume, remaining 180 degrees apart.
Now, researchers aim to look for quantitative evidence of complex, large-scale migration of sand dunes in the desert. To do so, they will make use of satellite images which will allow them to track clusters of sand dunes over longer periods, in order to see whether or not measures of diverting the migrations of sand dunes is effective or not.