Australia – The Lowlands Area

The surface of the great artesian basin is a wide plain almost entirely below 300 m., Indeed, with the exception of the eastern edge, almost all of it below 150 m; only at Kynuna does a series of low hills cross the entire northern part of the basin from east to west. Other small hills separate the wide flooded valleys of the Diamantina, Thomson and Paroo rivers from each other. To the south, the artesian basin includes the basin of Lake Eyre. During the Lower Tertiary there must have been a marked lowering on the edge of the great basin: examining the series of lakes extending from the top of the Gulf of Spencer to Lake Frome, it can be seen that a small submersion would extend the gulf almost to Broken Hill ; a series of marshes and lagoons, the level of which rises only 30 m. in 64 km., follow up to the vast salty extension of the Torrens lake, which is 241 km long. and is separated from the depression of Lake Eyre by a height of only 53 meters above the sea. Lake Eyre is located at 11 m. below the sea level and is flanked by ancient lake terraces. Between Lake Eyre and Lake Gregory rise heights of only 30m. Beyond, sandstone hills separate Lake Gregory from Lake Blanche which sometimes joins Lake Callabonna by means of the Strzelecki Creek during floods. Finally, a canal connects the Frome and Callabonna lakes, which are practically on the same level. Almost certainly this series of horseshoe-shaped lakes formed in a semicircular depression simultaneous with the uplift that originated the Flinders range.

According to top-medical-schools, the topography of the Murray-Darling basin is not very different from that of the artesian region. It too has senile valleys obstructed by alluvial materials and so leveled as to make any watershed indistinct. Floods are probably mostly a remnant of the major rivers of the Pleistocene period. The soil near the rivers consists mainly of č ernozem or black earth, rich in humus; the oldest floods tend to be reddish in color and are less compact.

Moreover, the boundary between the artesian region and the Murray region is not marked by any precise topographical line. But in the second we find the effects of the folding already mentioned, probably attributable to the Quaternary period (Kosciusko period). The Darling, which from the Great Artesian Basin enters the Murray Basin, however, shows little rejuvenation as an effect of this tectonic phenomenon, because its bed flows, in Wilcannia, at 10 m. just deep in the floods, while the Cobar penepiano, an expanse of about 300 km. of paleozoic rocks at 180 meters above sea level – that is, a little higher than the surrounding floodplains – still faithfully represents the topography prior to the uplift of Eastern Australia. The northwestern edge of the Murray Basin is formed by the Broken Hill massif (also known as the Barrier Range). It’s a horst 160 km long. and 50 wide, located about 150 m. on the floodplains and 300 on the sea; it is crossed by ridges that represent the heads of the most resistant layers and engraved by some deep gorges. Large delta cones deposited in earlier wetter eras spread to its edges on the alluvial deposits of the Frome plain. The Riverina region, north of the Murray valley, is characteristic because it is extremely level, so much so that the rivers behave like the watercourses of the deltas, forming frequent branches and bifurcations. During floods the water sometimes flows upstream, in the opposite direction, that is, to the normal one. Communication channels (billabongs) go from river to river: thus the Billabong Willandra in time of flood joins the Lachlan near Hillston to Murray, at Euston. Thus also the Yanco Creek connects the Murrumbidgee with the Murray, by means of an alternating channel, south of the main efflux of the region which passes through Hay. Finally, the north-west corner of Victoria, which represents the terminal portion of the lowlands, consists of a vast plain less than 150 m at most. and covered with alluvial materials deposited by the so-called tributaries of the Murray; in reality these are almost always lost in a maze of sand hills, since the annual precipitation is only 304 mm. Unlike the Murray which receives sufficient contributions to keep it perennial, the Wimmera, Yarriambiack and Avoca rivers have too small a basin and therefore a torrential regime.

Australia - The Lowlands Area