Revealing the intricate dune-dune interactions of bidisperse barchans

TL;DR

This study investigates how bidisperse and monodisperse grain compositions affect the interactions and morphology of barchan dunes, revealing new interaction patterns and conditions for collisions in natural and extraterrestrial environments.

Contribution

It introduces experimental analysis of bidisperse barchan interactions, highlighting the effects of grain size mixtures on dune morphology and collision dynamics.

Findings

Transient stripe formation in bidisperse dunes

Interaction patterns depend on grain concentration

Conditions identified for upstream larger barchans during collisions

Abstract

Three dimensional dunes of crescentic shape, called barchans, are commonly found on Earth and other planetary environments. In the great majority of cases, barchans are organized in large fields in which corridors of size-selected barchans are observed, and where barchan-barchan interactions play an important role in size regulation. Previous studies shed light on the interactions between barchans by making use of monodisperse particles, but dunes in nature consist, however, of polydisperse grains. In this paper, we investigate the binary interactions of barchans consisting of (i) bidisperse mixtures of grains and (ii) different monodisperse grains (one type for each barchan). We performed experiments in a water channel where grains of different sizes were poured inside forming two barchans that interacted with each other while filmed by a camera, and we obtained their morphology from image processing. We observed that a transient stripe appears over the dunes in cases of bidisperse mixtures, that interaction patterns vary with concentrations, and that different interactions exist when each barchan consists of different monodisperse grains. Interestingly, we found the conditions for a collision in which the upstream barchan is larger than the downstream one, and we propose a timescale for the interactions of both monodisperse and bidisperse barchans. Our results represent a new step toward understanding complex barchanoid structures found on Earth, Mars and other celestial bodies.