Aeolian transport, barchan dunes, and vegetation stabilization
Barchan dunes form when sand supply is limited and wind is unidirectional — sand avalanches down the steep slip face while horns migrate faster than the bulkier center, creating the characteristic crescent shape. Transport rate scales with the cube of wind speed (Bagnold's law: q ∝ u³). Vegetation dramatically reduces migration by increasing surface roughness and binding sediment; colonization by marram grass (Ammophila) can stabilize foredunes entirely, converting mobile barchans to parabolic or longitudinal forms.