Landforms from Space
The catchment area of the Roper River extends over 80 000 square kilometres, draining south-eastern Arnhem Land to the north and reaching westwards almost as far as Katherine. Torrential summer rains flood out of Arnhem Land and spread across the low-lying plains, forming massive wet-season swamps. Pockets of dense woodland clad a series of low mountain ranges to the north and south of the river. The river tidal flats spread over more than 1 000 square kilometres and comprise a network of intricate deltas and extensive mangroves.
Lake Eyre is Australia's largest salt lake and is situated within a major internal river drainage system of the interior lowlands in one of the driest regions in the country. The salt accumulates in the lake after being washed from underlying marine sediments. When in its usual dry state, the lake bed is a glistening sheet of white salt.
The lake was named after Edward Eyre who was the first European to sight it in 1840. It actually comprises two lakes, North Lake Eyre and South Lake Eyre, which are connected by a narrow channel. The lake appears partially full at the time of the adjoining imagery (March 1997) and the vegetation response to the rains can be clearly seen along the tributaries draining into South Lake Eyre.
To the east and north-east of the lake lie the Tirari, Strzelecki and Sturt Stony deserts, a most inhospitable and bleak environment. Almost three-quarters of the run-off from the 1.3 million square kilometre catchment finds its way via an intricate network of channels known as the Channel Country through these deserts towards Lake Eyre, although most of the water is lost through evaporation or absorption.
When the lake does fill, it becomes temporarily Australia's largest lake as it spreads out to 9 500 square kilometres and at its deepest point and reaches almost six metres. This has occurred only three times this century, the latest being in 1989. The bed of Lake Eyre is the lowest area in Australia at 17 metres below sea level.
A myriad of stream channels work their way west to the Norman River which, together with the Saxby and Flinders Rivers, drain northwards towards the extensive depositional plains and shallow waters of the Gulf of Carpentaria. During the wet season from October to May these streams transform the surrounding low, flat, arid plains into inland seas. The engorged rivers may eventually overflow their banks to join each other over tens of kilometres, effectively isolating communities.
The course of Kyabra Creek, which is fed by hundreds of tributaries, curves its way westwards into the entanglement of channels that form the vast floodplains of Cooper Creek. So gradual are the gradients of the land that floodwaters slow down, spread out and break up into hundreds of small braided channels. The floodplains are irregularly covered by water overflowing from the maze of channels which form a large part of the downstream reaches of the Georgina, Diamantina and Thomson rivers, rising to the north and north-east. Flood waters moving down these rivers occasionally drain into Lake Eyre, although more often they dry up before ever reaching the lake. The floodplains are not inundated every year so during dry times they contain just a few swamps and permanent waterholes.
Very high rainfall and fertile basalt soils combine to produce luxuriant tropical rainforests cloaking this part of the Eastern Highlands, an ancient, dissected volcanic plateau containing some of Queensland's highest peaks, including Bartle Frere (1 611 metres). Patterns of agriculture are apparent along the coastal hinterland (sugar cane), as are the rich farming and dairying land of the Atherton Tableland lying to the south of Lake Tinaroo.
The chequer-board appearance of rich agricultural lands surrounding Lake Goran are a dominant feature of the Liverpool Plains. Here, a mixture of cereal grain and sheep farming predominate with good soils and rainfall contributing to the high wheat yields in the area. The serpentine Lake Keepit on the Namoi River between the two major commercial centres of Tamworth and Gunnedah is an important provider of irrigation water for other agricultural activities such as lucerne, vegetables and cotton.
To the south, the basalt-capped Liverpool Range swings north-east as a spur of the Great Dividing Range with an encircling rim of ranges continuing north-west to the prominent volcanic remnants of Mount Kaputar which stands at 1 508 metres.
Australia's highest landscape region consists of a series of plateaux raised by the gradual elevation of plains millions of years ago. Straddling the Great Dividing Range, it includes Mt Kosciuszko and numerous towering peaks exceeding 2 000 metres, countless precipitous slopes, plunging gullies, glacial lakes and valleys. The forces of erosion, glaciation, faulting and folding have all played a part in variously sculpting a dramatic landscape. The region is Australia's the largest alpine area, with snow a dominant feature of the landscape above 1 600 metres from July to November. Below this height, the climate of the ranges encourages strong growth of native forests. During spring and summer, large quantities of snowmelt run off and are diverted into the surrounding lakes of the Snowy Mountains hydroelectric and irrigation scheme.
The course of the River Murray, which forms most of the border between New South Wales and Victoria, can be traced from its source in the southern Snowies to the northern arm of the enormous Lake Hume and west as it snakes between the twin cities of Albury and Wodonga. North of Albury, the agricultural activity reveals intricate patterns of cereal cropping which subtly gives way in the east to more extensive sheep and cattle grazing.
The patterns of farming apparent across the Gippsland plain reflects the fertility of the river basin which, at a time of lower sea levels, drained westwards and emptied through Port Phillip Bay. Flanked by the foothills of the Great Dividing Range to the north, this once timbered region is now primarily dairying country, with some forestry evident to the south and brown coal mining further west.
Six major rivers fill the Gippsland lakes, Australia's largest inland waterway with an area of about 400 square kilometres dominated by Lake Wellington. The lakes have been formed mainly by two coastal dune barriers, one an old sea cliff to the west of Lake Reeve which is squeezed against the other, the taper thin Ninety Mile beach. The lake waters escape through a narrow channel cut to the north at Lakes Entrance, which also provides access for boating.
The city of Hobart is situated at the mouth of the Derwent River, a relatively short river but wide and deep in its estuary. Urbanisation is evident for some considerable distance along both sides of this rift valley which was formed by faulting. Several kilometres south-west of the city the land is heavily forested and mountainous, rising steeply to Mount Wellington at a heights of 1 270 metres.
The ragged and deeply indented coastline is very distinct, a result of ancient rises in sea levels which drowned the lower reaches of the Derwent and Huon Rivers. In places, steep walled cliffs expose impressive erosion-resistant dolerite columns. Numerous sharply angular islands have been formed, notably the large, tenuously connected Tasman Peninsula to the east, Maria Island with its wafer thin sand isthmus to the north and the elongated Bruny Island to the south-west adjacent to the Huon River.