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

TL;DR

This study demonstrates that two distinct dune growth mechanisms can occur simultaneously in a landscape-scale experiment, influenced by sand availability and wind conditions, with detailed analysis of dune formation and dynamics over four years.

Contribution

It provides empirical evidence of coexisting dune growth mechanisms and validates theoretical models with high-resolution field data.

Findings

Two different dune orientations can develop under the same wind regime.

Dune shape transitions from dome to barchan and asymmetric forms.

Wind reversals influence dune alignment and growth.

Abstract

In landscape-scale experiments at the edge of the Gobi desert, we show that various dune types develop simultaneously under natural wind conditions. Using 4 years of high-resolution topographic data, we demonstrate that, depending on sand availability, the same wind regime can lead to two different dune orientations, which reflect two independent dune growth mechanisms. As periodic oblique dunes emerge from a sand bed and develop to 2 meters in height, we analyze defect dynamics that drive the non-linear phase of pattern coarsening. Starting from conical sand heaps deposited on gravels, we observe the transition from dome to barchan and asymmetric barchan shapes. We identify a minimum size for arm elongation and evaluate the contribution of wind reversals to its longitudinal alignment. These experimental field observations support existing theoretical models of dune dynamics boosting confidence in their applicability for quantitative predictions of dune evolution under various wind regimes and bed conditions.