Morphodynamics of the Liwa Megabarchans as a Titan Analog : Reworking of Giant Linear Dunes by Unidirectional Winds

English Abstract:

We document the sand dynamics at the unusual megabarchans that begin abruptly at the Liwa Oasis in the northeastern Rub’ Al Khali desert in the United Arab Emirates (U.A.E.).  Their close, regular arrangement is not consistent with a conventional barchan corridor, and we propose that the dunes must have grown to their great (>100m) height as linear dunes, which are presently still more evident to the south and east of Liwa, but are now exposed to a unidirectional wind regime that forms a consistent slip face orientation and is eroding the linears into discrete but ephemeral barchan forms. We estimate present-day sand fluxes of ~4 m³/yr/m from the ~0.1 m/yr advance of megabarchan slip faces and from combined field and satellite observations of the migration of small barchans across the interdune areas. These suggest a ~20kyr timescale  to evolve into the present disequilibrium  configuration, consistent with estimates of paleowind changes in Arabia. We note recent flume experiments demonstrating hooked barchans and a linear-barchan transition in mixed winds, and that similar linear-megabarchan transitions are seen on Saturn's moon Titan.