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Despite being inanimate objects, sand dunes have been found to communicate in ways that could help us learn how they might threaten infrastructure.
A team of researchers from the University of Cambridge has performed an experiment using sand dunes that suggests it is possible for two objects to communicate, without actually having a single thought.
In a paper published to Physical Review Letters, the team said it observed two sand dunes working together in order to repel their downstream neighbours. Using a special ‘racetrack’, two identical sand dunes were shown to start off close together, but drift further apart over time.
Acting like billiard balls
The interaction was controlled by turbulent winds from the upstream dune, which pushed the downstream dune away. By understanding how this natural phenomenon behaves, we can better understand the migration of sand dunes, which can threaten shipping channels and bury key infrastructure.
A dune shape forms when a pile of sand is exposed to wind or water flow. Whether formed in a desert or on riverbeds, they tend to form in groups to create dune fields or corridors.
When it comes to migration, small dunes typically travel faster than their larger counterparts, but what has eluded researchers for some time is if and how dunes interact in a field.
One theory is that they collide until they form one giant dune. The second is that they collide like billiard balls until they are both of equal size. However, these theories haven’t been confirmed yet, according to the study’s first author, Karol Bacik.
Surprising discovery
The dune racetrack in this experiment is quite unique, the team said, as instead of a typical straight water flume to measure the dunes’ movement, it built a circular flume that can be observed for hours using high-speed cameras.
“Originally, I put multiple dunes in the tank just to speed up data collection, but we didn’t expect to see how they started to interact with each other,” Bacik said.
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. This came as a surprise to the team as it thought both would consistently move in unison because they were the same size and volume.
Crucially, the pattern of flow across the two dunes was observed to be different. The flow was deflected by the front dune, generating ‘swirls’ on the back dune and pushing it away.
As the experiment went on, the dunes spread further apart until they formed an equilibrium on opposite sides of the circular flume, 180 degrees apart. The team will now try to see this phenomenon in large-scale and complex dune migration in deserts using observations and satellite images.
