Real barchan dune collisions and ejections

From high-resolution satellite imagery of barchan sand dunes, we provide geomorphological evidence of collisions that result in the ejection of a barchan from the wake of another barchan dune. Previous interpretations suggest this outcome is evidence of soliton or solitary wave behaviour; however, the physical mechanisms for mass exchange are not fully understood, resulting in debate. Our evidence and interpretation indicates that mass is transferred to the upwind barchan by shadowing a portion of downwind barchan's stoss slope. Turbulent, unsaturated airflow erodes the surface between the dunes, creating a smaller dune that ejects from the wake region. Previous observations lacked the spatial resolution required to document this process; therefore, our observations clarify the collision dynamics of barchans. A broader implication of our observations is the role of collisions in maintaining an "equilibrium" size distribution in barchan swarms. Citation: Hugenholtz, C. H., and T. E. Barchyn (2012), Real barchan dune collisions and ejections, Geophys. Res. Lett., 39, L02306, doi:10.1029/2011GL050299.