Evolution of a coastal transgressive dunefield to a parabolic dunefield, Canunda dunes, South Australia

Abstract

Various studies have detailed the evolution of barchan dunes to parabolic dunes and a very few studies describe the evolution of coastal transgressive dunefields and continental sand seas to parabolic dunefields. This study examines the evolution and transformation of a 12 km long portion of a formerly large (~50 km along-coast), active, transgressive dunefield (coastal sand sea or erg) dominated by transverse dunes to a coastal barrier dominated by parabolic dunes. A GIS study of vegetation cover change from 1950 to 2017 was conducted, and a stereographic analyses of 1945 to 2020 aerial photography was carried out to determine morphological changes across the dune system. Historical rainfall, aeolian drift potentials, and rabbit numbers are examined as possible drivers of change, and rabbit numbers most strongly correlate with vegetation change. The vegetation cover of the greater dunefield increased in the study area from 26 % cover in 1950 to 54 % by 2020. A largely unvegetated transgressive dunefield dominated by transverse dunes evolved into a parabolic dunefield in <70 years. Vegetation colonisation primarily took place from landward slipfaces, by nebkha formation on dune lobe crests, from interdune swales and flats, and within deflation basins and plains. Vegetation colonisation also occurred above the backshore in the same period. Aeolian landform units such as marginal ridges, nebkha fields, deflation basins and plains, dune ridges, remnant knobs, parabolic dunes, and a foredune-blowout complex were formed as the dune field was colonised and stabilised by vegetation growth. The study provides far greater detail on how vegetational and morphological changes take place as a transgressive dunefield evolves into a parabolic dunefield.