The mystery of mini-dunes: how small sand hills appear on beaches and in deserts
Have you ever noticed tiny sandy scallops suddenly appearing right under your feet on the beach?
These mini-dunes can grow in half an hour and then disappear as if they never existed. Scientists have long puzzled over how they form in the first place
A team of researchers from the University of Southampton and research centres in France, the US and the UK has finally uncovered this natural trick. And now we not only have an explanation, but also a computer model that can predict the appearance of such dunes - even on Mars!
Details: Rambert, Camille et al, Modelling the dynamics of aeolian metre-scale bedforms induced by bed heterogeneities, Proceedings of the National Academy of Sciences (2025). DOI: 10.1073/pnas.2426143122. doi.org/10.1073/pnas.2426143122
🧪 What are mini-dunes?
So-called 'proto-dunes ' are tiny sand formations up to a few centimetres high. They can appear in 30 minutes, especially after windy weather, and just as quickly disappear under waves or a new wind. Unlike the giant dunes in the Sahara Desert, which take centuries to form, these mini-versions are true sprinters in the world of geology.
🌬️ How do they appear?
Scientists conducted experiments in the Namib Desert using ultra-precise laser scanners. They found that when the wind drives grains of sand across a hard surface, they don't just roll - they bounce up to a metre high. And when they fall on a looser area, that's where the dune starts to form.
As soon as a tiny bump appears, it changes the airflow. This creates a snowball effect: the wind brings more and more sand, and the dune starts to grow.
🌎 What happens next?
Using the data collected, the scientists from Paris have created a computer model that accurately reproduces how dunes grow in different environments, from dry Namibia to the wet coasts of Colorado and Norfolk. It also helps us understand why dunes grow in some places and disappear in others.
And the most exciting part: now they want to use this model to study mini-dunes on Mars. Yes, there's sand and wind there, too - and quite possibly the same beach scallops, only Martian.