5.1.5 Hummocky dunes sub-dominant (south east of linear dunefields)

5. North Western Dunefields and Plains (DP)
5.1 Calcareous dunefields

Clusters of sub-round dunes occur on an undulating plain in the south-eastern Mallee, extending north-easterly from Beulah West to Swan Hill, a distance of some 130 km. The northern boundary abuts linear dunefields and is thus clear. This boundary appears to approximate to the local southern limit of the Blanchetown Clay. The southern and eastern boundaries are irregular, but clearly defined from riverine plains of the Richardson and Avoca Rivers. Alluvial terraces also cross the unit from south east to north west along the Tyrrell and Lalbert Creeks. In the southwest the unit abuts 5.5.1 which lacks dunes. However detailed field work and suitable imagery are needed to locate the boundary accurately. The plains on which the dunes occur are generally subdued with weakly-developed stranded ridges. Low hummocky dunes occupy about one quarter of the unit. On subdued plains they tend to occur in clusters which may be as much as 3 km across. The pattern may reflect variation in the clay content of the underlying weathered Parilla Sand.

Gilgaied clays (Vertosols) are the most widespread soils, occupying the broad subdued plains, the elongated plains between stranded ridges and the lower slopes of dunes and ridges. Medium-textured calcarosols occur on the upper slopes of dunes and ridges.

Agricultural production is lowered on the clay soils by limited penetration of rainwater and by inherent salinity and sodicity of the gilgai puffs. These effects increase with increasing aridity towards the north. The wind erosion hazard is high only on upper western dune slopes. Seepage salinity has not been noted.

Vertosol in gilgai shelf on plain in southern Mallee

[<img src=../../vroimages.nsf/Images/geomorph_5.1.5/$File/515_hummocky_dunes_sub_dominant1.jpg height=162 width=300 align="" alt="5.1.5 Hummocky dunes sub-dominant (south east of linear dunefields)" border=0>]

Page Top