Coexistence of two dune growth mechanisms in a landscape-scale experiment

Dune fields are recognized both by the occurrence of periodic bedforms and isolated dunes of different shapes and orientations. Nevertheless, there are still no field examples of whether this apparent duality results from synchronous dune growth, and on what timescales. Here, by leveling neighboring parcels of a dune field, we develop landscape-scale experiments with controlled initial and boundary conditions to test the influence of sand availability on dune formation. Starting from a flat sand bed, we observe the emergence of periodic dunes and measure for more than 3 years how they grow as they interact with each other. Over the same time period, by regularly feeding sand heaps deposited nearby on a non-erodible bed. we observe how dune shape changes, eventually leading to the elongation of isolated dunes with a different orientation. These experiments are unique by their size and duration. Under natural conditions, they show that the same wind regime can be associated with two dune growth mechanisms according to sand availability. The coexistence of these two dune growth mechanisms provides a basis for examining the diversity of dune shapes on Earth or other planetary bodies depending on local climatic conditions.