Only a few uplands interrupt the sweeping plains that occupy most of South Australia. The highest point in the Sate, Mount Woodroffe, stands only 1435 metres above sea level, and few peaks exceed 700 metres.
The landscape is a result of the interplay through time between the earth's crust and external forces. Rivers have been and remain the dominant agency shaping the surface, but climatic conditions have varied through geological time, and glaciers and the wind have also contributed to the shaping of the land surface. The advent of man has caused accelerated erosion and deposition.
Earth movements have been frequent, but there have also been periods of relative stability when rivers reduced the land to plains of low relief. These plains were deeply weathered, frequently resulting in the formation of duricrusts (concentrations of particular minerals) that become hard on drying, and which today form hard cappings. Remnants of duricrusted plains are prominent, with laterite in the southern regions, and silcrete, calcrete and gypcrete in the drier interior. Elsewhere the mantle of weathered material has been stripped away exposing bare rock in 'etch' surfaces. Another kind of rock plain, the 'exhumed' surface, is widely preserved at the margin of the craton where the later Mesozoic sediments that once covered the earlier land surface have been stripped. Finally, extensive depositional plains of riverine and lacustrine origin occur in the Lake Eyre Basin.
Uplands in Crystalline Rock
Granite and Gneiss Hills
In the Ranges of the Northwest the rocks of the Musgrave Ranges are sheared and contorted and the terrain is rugged, tending to an 'all slopes' topography. Less stressed rocks from the Everard Ranges which consist of ordered rows of bald, rounded hills. Dolerite and other basic dykes form linear ridges. The Indulkana Range has a summit surface and is eroded in folded Palaeozoic quartzites. Many residual hills (inselbergs or 'island mountains'), such as Mount Lindsay, rise abruptly from the desert plains to the south. Granite inselbergs also occur in many parts of the northwestern interior and on northern Eyre Peninsula. Typically they are dome-shaped hills with well-developed massive sheet structure, rock basins and gutters, hollows and caverns, and concave or flared basal slopes.
The Hiltaba Hills are a region of granite domes characterised by large-scale sheet structure (convex upward thick slabs of rock).
Ancient Volcanic Massifs
The Gawler Ranges form a massif of domes defined by east-west and NW-SE and SW-NE fractures developed in Proterozoic volcanics. Sheet structure is well developed and is responsible for the rounded shape of the hills. A rocky summit surface of Mesozoic age, with a few monadnocks, slopes gently down to the north. Remnants of a late Proterozoic exhumed surface are exposed north of Nonning. Drainage is mostly impeded, resulting in many large 'salinas' (salt pans). To the south the former Corrobinnie and Narlaby river channels were blocked by coastal dunes between Ceduna and Streaky Bay.
The Cultana Hills consist of old volcanic rocks and granite shaped into rounded hills.
Younger Volcanic Hills
The Mount Burr Range consists of fifteen volcanic centres (cones, domes and maars) more than 20,000 years old.
The Southern Volcanic Hills comprise several prominent cones, craters and maars, including the well known Mount Gambier and Mount Schank. Mount Gambier is about 4800 years old and all the volcanic features in the area are less than 10,000 years old.
Uplands in Sedimentary Rocks
Plateau (flat-lying sediments)
The Arcoona Plateau, of probable late Cretaceous age, was developed on dissected Proterozoic rocks with quartzites prominent. The eastern margin of the upland is faulted. Slopes are typically faceted; scarp foot valleys and false cuestas, some capped by silcrete, are common.
The Tent Hills region comprises isolated plateaux and mesas. Scarp foot valleys and false cuestas are again well represented.
Ridge and Valley (folded sediments)
Sediments in the Adelaide Geosyncline were folded and faulted in the early Palaeozoic. The upland chain was reduced to low relief during the early Mesozoic when deep weathering under torrid conditions caused the widespread development of laterite.
The early Cainozoic saw the widespread reactivation of faults, the formation of the precursors of Gulf St Vincent and Spencer Gulf, and the disruption of the old land surface. The ranges were again uplifted, and subsidence of the Lake Eyre region began. Some of the regions developed on these folded sequences comprise typical ridge and valley forms. Elsewhere the lateritic duricrust remains prominent.
The Parndana Plateau which comprises most of Kangaroo Island is a dissected lateritic plateau. The coastal scenery is spectacular.
The Mount Lofty Ranges are a long narrow uplifted block bounded by prominent fault scarps. Exhumed Permian glacial features occur in the Inman Valley and at Hallett Cove. A lateritized surface is well preserved on Fleurieu Peninsula, but to the north the duricrust has largely been stripped away, leaving an etch surface. Within the Ranges the most prominent hills are underlain by quartzite. Granite forms boulder-strewn outcrops, and the granite islands of Encounter Bay are literal inselbergs.
The uplands of Eyre Peninsula are developed on folded metasediments. The Lincoln Upland is a dissected lateritic plateau tilted down to the west and bordered on the east by a fault scarp. The south-west to north-east trend of the underlying Precambrian rocks, imposes a strong topographic grain. Blue Range is a laterite-capped mesa, and there are various outliers underlain by either quartzite or gneiss.
The Cleve Hills consist of ridge and valley with remnants of a high plain. The more prominent ridges are of quartzite. The uplands are bounded to the south and east by fault scarps.
The Denison and Davenport Ranges, eroded in folded Proterozoic rocks, are bounded on the east by a prominent fault scarp; there is a pronounced etch type summit surface.
The Flinders Ranges consist of ridge and valley. The upland margins are faulted in the north, but elsewhere are ramparts of hard rock. The pattern of ridge and valley follows the pattern of folds, although diapirs produce irregularities. Around Mount Painter, 'all slopes' topography is developed on the older granitic rocks. Through most of the upland, however, ridges of quartzite, and to a lesser degree limestone and tillite, are dominant. Varied dip of strata produces various ridge forms - cuestas, and with increasing inclination of beds, homoclinal ridges and hogbacks. Where the ridges are regularly dissected, 'flatirons' are formed. Plains and valleys are eroded in argillaceous rocks and limestone. There are major inter-montane basins around Hawker, Orroroo and the former site of Willochra.
Remnants of a Late Mesozoic summit surface are preserved in the north around Mount Babbage. A related surface, possibly riverine, extends into the central and southern Flinders Ranges. Drainage is largely adjusted to structure, but there are notable transverse elements. The present relief pattern was essentially developed some 60 Ma following an early Cainozoic uplift, but the Miocene saw further uplift and renewed stream incision, causing dissection of the old valley floors.
The Mid North Ranges are dominated by ridges and valleys developed on folded sediments. Laterite is preserved on some of the crests, silcrete on midslopes. Major rivers such as the Broughton and Light cut across the structure, but long strike streams have eroded the more extensive valleys. The Barossa Valley is an alluviated area occupying a fault-angle depression.
The Olary Upland is a region of low but rugged, rocky ridges and bosses, with broad valleys and inter-montane alluvial plains.
Much of the interior of South Australia is arid, although it was humid in the geologically recent past. Other regions that are now semi-arid were formerly deserts, and the landscape reflects that former aridity.
Active Sand-ridge Deserts
The Simpson Desert is an extensive field of SSE-NNW trending parallel sand-ridges with prominent Y junctions. The dunes stand between 10 and 39 metres above the interdune corridors and are low and closely spaced in the west, high and widely spaced in the east. The ridges are asymmetrical in cross-section. The dunes have been built by winds flowing from the south-east and south-west. The sand is derived from playas and floodplains.
The Tirari, Strzelecki, Great Victoria, Anna and Hamilton deserts are similar to the Simpson Desert. The trend of sand-ridges swings across the north of the State from WNW-ESE in the Great Victoria Desert, though east west to SW-NE and south-north in the Strzelecki Desert. Floodplains, lagoons and areas of stony desert are minor elements.
The Tuckey Plain is a field of linear dunes similar to those of the Simpson Desert, although now stabilised by vegetation. The dunes trend north-west to south-east except near topographic obstacles. The dunefield occupies a rolling plain, cut in granite and gneiss, but covered with calcrete. In the north are many isolated, intricately sculptured granite uplands.
The Maitland Plain, a high plain with no surface drainage, is bordered on the east by the Kulpara fault scarp. Remnants of a Pliocene-Pleistocene land surface, capped with ferricrete, are preserved in the north-east. The high plain also carries a calcrete crust and is traversed by north-west to south-east trending relic linear dunes. Caves are developed in limestone near Curramulka.
The Murray Plain is developed on Tertiary calcareous sediments capped by massive calcrete and overlying a granite inselberg landscape, parts of which are exhumed where the River Murray has cut through the sedimentary cover (for example, at Mannum). The high plains are characterised by fields of west-east trending relic dunes. In the limestone areas between the dunefields, broad shallow depressions, recently developed sinkholes and some cave systems occur. There are no surface streams except in the west where streams from the Mount Lofty Ranges flow to the River Murray.
The Pirie-Torrens Plains are alluvial, with prominent WNW-ESE and south-west to north-east trending dunes. The Flinders Ranges are fronted by dissected pediments and by alluvial fans south of Wilkatana.
Stone (gibber) Deserts
The Sturt Stony Desert, Stuart Range and Etadunna Plain are covered by gibber largely derived from the disintegration of silcrete. There are a few large linear dunes.
The Tarcoola-Kingoonya Plains consist of several types of desert plain, but are dominated by gibber. Silcrete underlines much of the plain and exposures of granite and porphyry result in bosses and platforms. Dunes occur in the east.
The Wertaloona Plain is an alluvial outwash plain located in the scarp foot zone of the uplands (hence piedmont - foot of the mountain) that includes alluvial fans derived from the Flinders Ranges and the Olary Uplands.
Salinas and Associated Plains
Lake Eyre is a large halitic salina (9324 square kilometres) which is located in the driest part of Australia. It stands some 17 metres below sea level. It is bounded on the west by a dissected linear fault scarp. The lake bed is occasionally flooded, and during these inundations beaches, spits, bars and other coastal features rapidly form. There is evidence of previous higher fillings of the lake.
Lake Torrens, some 5827 square kilometres in area, also occupies a tectonic depression bordered by the fault scarp on its western side. The gypsiferous surface is about 34 metres above sea level.
Lake Frome has a surface dominated by halite; it stands about 12 metres above sea level.
Lake Gairdner, about 8884 square kilometres in area, is an alluviated river valley. The bed is covered by a halite crust. It is surrounded by the red rounded hills of the Gawler Ranges, and islands of volcanics stand above the lake bed.
North Riverine Plains or Floodouts
The Macumba, Diamantina and Cooper plains consist of braided channels, lagoons and alluvial deposits of ephemeral rivers.
Southern Riverine or Lake Plains
The Adelaide Plains consist of alluvium derived from the Mount Lofty Ranges, with alluvial fans of late Pleistocene age fronting the uplands. Some mangrove swamps occur north of Port Adelaide; otherwise sandy beaches border the sea. Relic linear dunes occur in the north.
The alluvial Cummins Plain is dotted with salinas. The construction of drains has reduced the incidence of waterlogging, formerly a regular winter occurrence.
The Milang Plain consists of lakes Albert and Alexandrina and the associated alluvial flats, some of which are subject to flooding.
The South-East Plains comprise the Lucindale Flats and Hatherleigh Dunes. The flats form corridors with many swamps and lakes or lagoons separating the dune ranges. The flats are naturally subject to winter inundation, although most have now been artificially drained.
Karst plains are noted for their lack of surface drainage and for features due to solution of the limestone both at the surface and below ground.
Strong Karst (on crystalline limestone)
The Nullarbor Plain is a karst plain, underlain by Tertiary limestones uplifted during the Pliocene. In the west, the southern margin lakes takes the form of a spectacular line of coastal cliffs, but high dunes form a coastal fringe in the east. It is a lithological as well as a climatic desert as any rain that falls soon infiltrates underground. The surface is remarkably even and treeless, and is so flat that the transcontinental railway runs in a straight line for 483 kilometres. The even surface is deceptive, for dolines and very long caves are widely developed.
The Naracoorte Plain, developed on a Tertiary limestone, is noted for its deep, flooded sinkholes and caves, some of which are renowned for their intricate and spectacular stalactites and stalagmites, and for their fossiliferous deposits.
Weak Karst (on clastic limestone)
The Sheringa Plain is underlain by old lime-cemented calcareous coastal dunes. Hilly near the coast, and rolling and undulating inland, the topography reflects the old dune forms. The dunes buried an inselberg landscape. Between Streaky Bay and Port Kenny, and old granite forms have been re-exposed. High cliffs in cemented dune limestone alternate with inlets and beaches. Granite and gneiss are exposed at the base of many cliffs in shore platforms. Modern coastal dunes have been built behind beaches and spread inland in many places.
The Warooka Plain consists of a rolling karst plain developed in old calcareous coastal dunes. The calcarenite overlies granite and gneiss, and forms precipitous coastal cliffs.
The Vivonne Plain consists of rolling limestone dunes, with spectacular coastal scenery. Granite is exposed along the coast, notably at Remarkable Rocks. Several lakes or lagoons are impounded between the dunefield and the slope of the laterite plateau to the north. Modern coastal dunes are prominent. The development of Pleistocene dunes around American River unified Kangaroo Island, linking at least two former islands.
The Hatherleigh Dunes comprise a complex sequence of abandoned calcareous coastal dunes (or 'ranges') interspersed with the Lucindale Flats. The oldest dunes originated about 1 million years ago. Some of the dunes are simple forms, others are composite. In the south-east they run parallel to the coast but in the north-west have a disturbed pattern. Modern fore-dunes are prominent along the coast. The Coorong is a lagoon impounded in an interdune corridor.
The shallow seas around South Australia are scored by submarine canyons, some of which, especially the Murray Canyons, are of immense depth; many drainage lines of glacial and pre-glacial ages are still discernible. The steep, dissected, continental slope leads down to an apron of fans and thence to the abyssal plains and hills.