LANZHOU -- Scientists have recently revealed the formation and evolution mechanisms of megadunes on a global scale, shedding light on the long-standing scientific question of how high loose sand can naturally be piled, according to the Northwest Institute of Eco-Environment and Resources (NIEER) under the Chinese Academy of Sciences.

Breaking through traditional understanding, this joint study systematically clarified the distribution pattern and morphology characteristics of global megadunes, which are taller than 100 meters, and identified the dominant role of topography in such large-scale aeolian landforms, the NIEER said.

The study was carried out by NIEER researchers in collaboration with scientists from the University of California, Los Angeles (UCLA), Zhejiang University and multiple other research institutions worldwide, with the findings published in the journal Proceedings of the National Academy of Sciences (PNAS).

Dunes, a typical landform of arid regions found across the Earth and other extraterrestrial bodies, have long been studied, yet the factors governing their formation and maximum size remain poorly understood, explained Zhao Hui, a NIEER researcher.

"Megadunes taller than 100 meters have traditionally been attributed to constraints such as atmospheric boundary layer depth, substrate bedrock type and sediment supply. However, global mapping from our new study shows that megadunes preferentially form near mountains and within depressions in dune fields," Zhao said.

To investigate the mechanisms underlying megadune formation, the research team used a dune simulation model to examine how topography influences their evolution under conditions of ample sand supply and a constant wind regime.

The study found that more than 97 percent of the world's megadunes are concentrated in the Sahara Desert and the arid regions of Asia. Abundant sand sources and strong winds provide the basic conditions for the growth of megadunes. By contrast, deserts in Australia rarely develop into megadunes due to relatively high vegetation cover and limited sediment transport.

Simulation results indicate that topography plays a key role in megadune formation by continuously shaping the spatial heterogeneity of wind fields and sand sources.

Both mountain-like and basin-shaped topographies generate abrupt shear stress gradients that trigger rapid, localized sand accumulation. Compared with the gradual evolution on flat terrain, mountain-depression settings accelerate dune coarsening and megadune growth through enhanced sand flux convergence and increased collision rates among migrating dunes, the simulation results showed.

"Our study not only deepens the understanding of the formation process of dune landforms in arid areas of the Earth, but also provides an important theoretical basis for the further study of aeolian landforms on extraterrestrial bodies," Zhao said.