Dune fields, a key to understanding the climate of other “Earths” in the Solar System

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Dune fields, with their periodic patterns visible from space, are one of the most recognizable landscapes on Earth and other planetary bodies. The periodicity of the dunes can be directly associated with the atmospheric conditions in which the dunes develop. By understanding how these dunes form on Earth, scientists could deduce from these mechanisms the environmental parameters that have allowed the emergence of specific dunes on other planetary bodies.

Dune fields are generally associated with periodic patterns that are among the most recognizable landscapes on Earth and other planetary bodies such as Mars and Titan. They are also often the first landscapes observed by planetary exploration missions.

The periodicity of dunes is directly related to the properties of winds, landscape topography and sand grain transport. Understanding the mechanisms of dune formation would therefore allow scientists to access the atmospheric and environmental conditions in which dunes develop, including on other Solar System bodies. Dune fields are thus privileged objects of study in geomorphology research, i.e. the science that studies landscape formation.

Periodic dunes are generally formed by the process of instability. While many questions remain about the precise functioning of this mechanism, the overall process is well known: the wind pushes the sand, which grows and then subsides, forming dunes perpendicular to the wind direction, with a typical periodicity that emerges through an interaction between the wind, the topography of the landscape and the size and transport of the sand grains. This process of instability occurs when a large “sand availability” is present, i.e. when there is a large volume of sand under the dunes.

However, periodic patterns can also be found on dunes that grow on non-erodible, sediment-limited soils. These dunes lengthen and align themselves in the direction of the wind that forms them, and can extend for several kilometres. These dunes are thus formed through a mechanism of elongation growth, leading to the deposition at the end of the dune of sediments transported along the ridge by the action of opposing winds. However, unlike dunes formed by instability in areas with a high availability of sediments, the origin of the periodicity of dunes formed by elongation remains unknown.

Elongated dune fields: A. Taklamakan desert, China; B. On Mars (Scandia Cavi); C. Rub al-Khali Desert, Saudi Arabia. The arrows indicate the theoretical direction of the dunes from the wind or satellite data, depending on whether the dunes form on a non-erodible bed (red) or a large volume of sand (blue) © Gadal et al.

A team of scientists, including IPGP researchers, proposes through this paper a first attempt to explain the emergence of such a regular pattern. They show here, with the help of numerical simulations, that the mechanism of growth by elongation does not produce a pattern with a specific wavelength. Elongation periodic dunes appear to be a juxtaposition of individual structures, whose arrangement is due to regular reliefs at the field boundary acting as boundary conditions. This includes, among others, dune patterns resulting from bed instability, or ridge line reorganization induced by dune migration. Wavelength selection in elongated dune fields thus reflects the interdependence of dune patterns during their evolution.

References:

Gadal, C., C. Narteau, S. Courrech du Pont, O. Rozier, et P. Claudin. “Periodicity in Fields of Elongating Dunes”. Geology 48, no 4 (1 avril 2020): 343‑47. https://doi.org/10.1130/G46987.1

The LabEx UnivEarthS contributed to this research by funding the ex-Exploratory project “Formation of dunes and climate on Titan” (E1).