By modeling a desert where the wind blows in two directions, researchers have succeeded in observing and highlighting, for the very first time, the formation process and long-term evolution of two types of very large sand dunes: transverse dunes and longitudinal dunes. They have demonstrated that longitudinal dunes and barchans – croissant-shaped dunes formed in a unidirectional wind regime – are the most stable over time. Their results should provide a better understanding of how dunes and deserts evolve on Earth and also help to deduce important information concerning wind regimes on Titan or Mars, for example.