When dunes move together, structure of deserts emerges

TL;DR

This paper presents an agent-based model demonstrating how dune collisions in large desert fields lead to stable, structured patterns of dunes, explaining observed spatial arrangements in dense barchan dune fields.

Contribution

It introduces a novel agent-based modeling approach to explain the emergence of spatial dune structures through dune collisions and sand redistribution.

Findings

Large dune fields exhibit two regimes: dilute and dense.

In dense regimes, dune collisions stabilize the dune field.

Structured corridors of dunes form in dense regimes, matching observations.

Abstract

Crescent shaped barchan dunes are highly mobile dunes that are usually presented as a prototypical model of sand dunes. Although they have been theoretically shown to be unstable when considered separately, it is well known that they form large assemblies in desert. Collisions of dunes have been proposed as a mechanism to redistribute sand between dunes and prevent the formation of heavily large dunes, resulting in a stabilizing effect in the context of a dense barchan field. Yet, no models are able to explain the spatial structures of dunes observed in deserts. Here, we use an agent-based model with elementary rules of sand redistribution during collisions to access the full dynamics of very large barchan dune fields. Consequently, stationnary, out of equilibrium states emerge. Trigging the dune field density by a sand load/lost ratio, we show that large dune fields exhibit two assymtotic regimes: a dilute regime, where sand dune nucleation is needed to maintain a dune field, and a dense regime, where dune collisions allow to stabilize the whole dune field. In this dense regime, spatial structures form: the dune field is structured in narrow corridors of dunes extending in the wind direction, as observed in dense barchan deserts.