# Topography influences megadune distribution and morphology

## TL;DR

This study shows that the presence of mountains and depressions influences the formation and size of large dunes by altering wind patterns and sand accumulation.

## Contribution

The paper introduces a new framework linking topography, wind dynamics, and sand redistribution to explain megadune formation.

## Key findings

- Megadunes form preferentially near mountains and within depressions due to abrupt shear stress gradients.
- Mountain-depression settings accelerate dune coarsening and megadune growth through enhanced sand flux convergence.
- Topography modifies wind regimes, increasing dune aspect ratios as shear stress intensifies.

## Abstract

Global megadune distributions remain poorly characterized, with their formation mechanisms still debated. This study summarizes megadune distribution patterns at a global scale and finds that megadunes have distinct formation mechanisms and dynamic behaviors compared to normal-sized dunes. Simulation results reveal that both positive (mountain-like) and negative (basin-shaped) topographies induce abrupt shear stress gradients, which trigger rapid localized sand accumulation. In contrast to the gradual evolution observed on flat terrains, mountain–depression configurations accelerate dune coarsening and megadune development by enhancing sand flux convergence and increasing collision frequency among migrating dunes. This obstacle-driven evolution framework advances our understanding of aeolian sediment accumulation and megadune genesis across planetary surfaces.

Dunes are widely distributed on Earth and other extraterrestrial bodies, yet relatively little is known about what controls their maximum size. Earth’s megadunes (>100 m tall) have traditionally been attributed to constraints including atmospheric boundary layer depth, substrate bedrock type, and sediment supply. However, global mapping results presented here reveal that megadunes preferentially occur near mountains and within dunefield depressions. Megadune height-spacing transition from a power-law relationship to a near-normal distribution, and their aspect ratio (Ra) with height shifts from inverse to direct proportionality. To investigate their underlying formation mechanisms, we focus on how topography influences megadune development under conditions of sufficient sand supply and constant wind regime, using a dune simulation model. Simulation results indicate that both positive (mountain-like) and negative (basin-shaped) topographies generate abrupt shear stress gradients, triggering rapid localized sand accumulation. Compared to gradual evolution on flat terrains, mountain-depression settings accelerate the dune coarsening process and megadune growth through enhanced sand flux convergence and increased collision rates between migrating dunes. Critically, surrounding topography modifies wind regimes, elevating dune aspect ratios (Ra) as shear stress intensifies. Our proposed topography–aerodynamics–sediment redistribution mechanism for megadune formation on Earth and other extraterrestrial bodies demonstrates that terrain-induced wind regime heterogeneity is the fundamental control governing the formation and evolution of massive aeolian landforms.