5.2.1 Parabolic dunes

Within the Little Desert and Big Desert the landscape has been fashioned into a complex array of undulating sand plains, east-west aligned dunes and jumbled dunes. The largest individual areas of parabolic dunefields occur in the Big Desert in three east-west swathes to the west of the linear depression containing the Wimmera River system. The swathes are some 10-20 km wide and up to 90 km long. These dunefields include a broad ridge running south-east from the Pinnaroo Block as well as stranded ridges and associated swales. The northernmost swale crosses the fringe of the regional depression to the east of the Sunset Strip.

The parabolic dunes (jumbled dunes) are areas of juvenile dunes (Hills & Bowler 1995) with sediments defined as Lowan Sand (Lawrence 1966) and were derived from deflation of underlying Pliocene Parilla Sand (remnant stranded beach ridges). These parabolic dunes are often large, with sharp crests (not stabilised by vegetation), often enclose wide heathy sand plains and are interspersed with smaller, smooth-crested dunes of variable orientation with no defined drainage. The arms of the parabolic dunes trend south-west to north-east as do the present dominant strong winds, evidence that the landforms are young (Joyce et al. 2003).

Orientation of the dunes is variable, but mostly south-west to north-east. Large sub-parabolic forms with sharp crests are common, with arms opening towards the south-west and with slip faces to the south and east. The dunes tend to be irregular along their crests rather than straight or smoothly curved, and there may be small, barchanoid segments. The parabolic dunes often enclose large plains 1 km or more across. These plains may contain small sub-rounded to linear dunes of variable orientation. The small dunes are mostly smooth-crested.

The major soils are Rudosols. Humus has accumulated at the surface except on unstable dune crests. Below the humus there are deep, loose, yellow sands over the whole landscape. In profiles examined to the south of Murrayville, coarse sand predominated and carbonates were confined to occasional flecks. The reaction was neutral in the top metre or so, but alkaline below this. Values for all plant nutrients examined were low (exchangeable metal cations, nitrogen and potassium). Lowan Sand is also known to be deficient in trace elements such as copper and zinc.

Vegetation across the three deserts varies with the large shift in climate. Average annual rainfall declines from 500 mm in the Little Desert to less than 300 mm in the Sunset Desert, and temperatures increase in the same direction. In the Big and Little deserts heathlands predominate with vegetation communities including a range of woodland, heathland and mallee vegetation. Prominent communities include Shallow Sands Woodland, Plains Woodland, Sandstone Ridge Shrubland, Heathy Mallee and Lowan Sands Mallee. Other vegetation communities include Dunefield Heathland, Low Rises Woodland, Plains Woodland, Parilla Mallee and Red Swale Mallee. Red Gum Wetland and Seasonally Inundated Shrubby Woodland have also been found in wetter areas of the landscape.

An abundance of species includes genera such as Banksia, Xanthorrhoea and Epacris. These species sometimes form an understorey to mallee eucalypts, particularly along sheltered slip faces, the stands being known as ‘mallee-heath’. In the Sunset Desert, aridity is too great for heath which is replaced by mallee scrub with a prominent understorey of tea-tree.

Soil-landform unit	Unit description	Area (km²)
Big Desert jumbled dunes	Sandplain with jumbled dunes	478
Diapur ridge	Beach ridge and dunes	93
Goroke plains and rises	Plains with prominent ridges	118
Kiata rises	Gently undulating rises	19
Little Desert linear dunes	Linear dunes	22
Little Desert parabolic dunes	Parabolic dunes	1064
Nhill lake and lunettes	Lake-lunette	2
Wail parabolic dunes	Parabolic dunes	33
Woorak clay plains	Grey clay plains	18

Figure 14 jumbled dunes of the Big Desert

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