LANDFORMS OF DESERT: ~ 01
The Landforms of the Desert
Stony / Gibber Plains
In some areas there has been a greater deposition of stony
material and silty clays with the sand. Over long periods, winds
and other agencies have moved the sand away, leaving behind
the heavier stones or gibbers on the ground surfaces, forming
stony plains, often called gibber plains. The plains may be
extensive and cover wide areas, such as Sturt's Stony Desert.
Sand Dunes
Prevailing winds over thousands of years have in some areas
formed sand ridge or dunes which may be quite extensive.
Where the winds have blown in the same direction for
thousands of years, the dunes have been formed in the
direction of the winds. The Simpson Desert is a classical
example of this, for innumerable large sand dunes have been
formed in almost parallel rows, each extending for many kilometers in a
general south to north direction. These dunes are spaced at intervals,
sometimes close together, or even a kilometer or more apart, forming
distinct flat corridors between dunes which are known as swales,
There is variation in the colour of the sand. For example, where the
dune has been formed of sand which is close to adjoining
watercourses and flood plains, or other places where sand
TS
deposited by floodwater, it is chiefly yellowish In colour, which is the
general pigmented color of the quatz from which sand is formed.
Where the sand forming the dune has been carried for long distances
by the wind over extended periods of lime, it becomes coated with iron
oxide in its passage over the ground, giving the sand a reddish brown
coloring. Sand dunes formed by these sands present a reddish brown
colour which is characteristic of Central Australia,
Mesas
Amongst the interesting rock forms are the mesas which rise starkly above the surrounding
plains. These are remnants of ancient times when the land mass was at a much higher level
and the hard nature of their upper surface has resisted weathering. The typical mesa has a flat
top formed of hard material called a duricrust; the upper part has vertical sides and the lower
part is rugged and sloping, formed from the rock debris which falls with continued weathering.
In typical weathering patterns, the rock formation beneath the hard upper crust is softer
and weathers at a more rapid rate, so, as it falls away, the upper crust is unsupported and
breaks away, adding to the rocky debris below. Mesas may be in groups or isolated; they may
be very large, such as Mt Conner, or isolated column, for example, Chambers Pillar, a striking
rock column situated in the lower south east of the Northern Territory,
Saltpans, Saltlakes, Salinas
In many areas, various types of salts are dissolved from rocks, such as different forms of
calcium (lime and gypsum), common salt (sodium chloride), salts of magnesium (magnesium
sulphate-Epsom salts). The salts are carried in solution in water and, as the water rocky hills,
near the small settlement of Barrow
Creek.
The last group of ranges, the
Davenport-Murchison Ranges, are situated in a north-west direction, with the northern edges
of the range being traversed by the Davenport-Murchison Ranges, midway between Barrow
Creek and Tennant Creek, are the unique Devil's Marbles, which are a number of
superimposed large rounded granite boulders.