Lateral stability of central Australian longitudinal dunes

Abstract

Some authors consider that linear dunes migrate laterally on a grand scale, much as rivers move across floodplains. Others have concluded that lateral movement is limited in time and space. During the phase of dune initiation, small ribbons of sand formed in the lee of obstacles merge and coalesce to form recognisable linear dunes. Repeat observations demonstrate that mature sand ridges change position laterally a few metres either way within close limits defined by sand spillages on the slip or avalanche slopes that change orientation in response to changing sand-moving wind directions. This essay considers evidence by which to differentiate these two points of view. Supporting evidence for limited migration take the form of dunes resting on plinths of older alluvial substrates, some capped by gibber and that stand higher than adjacent interdune corridors. Such exposures show that the sand ridges have not migrated laterally during the last several tens of thousands of years. Migration is inhibited by clay cores, calcareous (calcrete) horizons, and the development of vegetated flanks. For these reasons, it is proposed that lateral migration be defined as a change of dune plan position that is greater than the maximum extent of sand deposition that develops in response to changes in the direction of sand-moving winds.