South Australia is notable for a remarkable diversity of coastal landscapes, many of which are of national and global significance. Numerous landscape-forming processes have influenced the evolution of this coastline. The current shape of the coastline relates to geological processes operating on a wide range of geological timescales that extend as far back as Archaean time (>2.5 billion years). As well as possessing many scenic wonders, the South Australian coastline presents numerous opportunities for scientific investigators to unravel the evolution of the coastline, with national and international implications.
As the broader continental-scale features of Australia influence the coastal landscapes of South Australia, the coastline should not be viewed in isolation from its hinterland. Australia in many respects is an old, flat and highly denuded continent, with the lowest topographical relief of all continents. Its intra-plate setting, high degree of tectonic stability, regional aridity, inland drainage (up to half the continent) and absence of major mountain ranges have significantly reduced the supply of terrigenous sediment to much of the coastline of South Australia. Few rivers reach the sea along the entire coastline of South Australia. Much of the State's drainage trends inland, and therefore the production of temperate sedimentary carbonates on the surrounding continental shelves is enhanced. Even on the Adelaide Plains, when the principal rivers (Little Para, Gawler, Light, Wakefield) do flow vigorously, their waters tend to temporarily exceed bankfull discharge and flood the adjacent flood plains, rather than reach Gulf St Vincent.
Desert dune fields related to intensified aridity and the latitudinal expansion of the arid zone during successive glacial events4 occur throughout extensive regions of inland Australia and along parts of the coastal margin. At times of glacial low sea level, when South Australia's gulfs were dry land, longitudinal dune fields extended across this broad region. On the northern Adelaide Plains, and to the east of Lake Alexandrina and the northern Coorong Lagoon (Big Desert), as well as on Eyre and Yorke Peninsulas, the dunes are very notable features of the regional landscape, sometimes dramatically truncated at the coast. They have contributed to coastal sediments.
The modern coastline: A general overview
The modern coastline was broadly established some 7000 years ago with the culmination of the most recent phase of postglacial sea level rise.