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Alan Fox, author of Wild Habitats, talks about the unusual habitat of Australia’ salt lakes, rather timely given that Lake Eyre is now filling up. Most cartographers drawing up maps of Australia use the typical convention of drawing the inland lakes in blue. Most however, only carry surface water after the random storm rains. But one of the greatest ironies of the global warming process is that the central and southern regions of Australia will become drier while the tropical north is likely to have greatly increased wet season cyclonic rain filling the southern flowing rivers running into Lake Eyre, one of the largest salt lakes in the world. So maybe this is one 'blue coloured' map lake that in 30 years or so, will be truly blue. However, at present, a vast number of the inland lakes should be white, representing their blistered white salty surfaces.
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| What really are salt lakes like?
A number of later inland explorers learnt the answers the hard way. Charles Sturt (1845) came upon numerous small lakes but it was John Eyre (1840 and 41) who discovered Lake Torrens and Lake Eyre South, who in all his expeditions became the 'Salt Lake King'.
The crusty salt on the surface of large salt lakes belies the fact that it is always wet beneath the salt crust, as the explorer Ernest Giles discovered when his camels and horses became bogged in the sticky, blue, toxic mud underneath. The salt lake that imperilled Giles was the great 300km long Lake Amadeus (shown left) north of Uluru and the ancient end of the Finke River. Lake Eyre lies at the bottom end of the Finke, Todd, Hay, Warburton and Diamantina rivers and Coopers Creek and has, over millions of years received all the dissolved salt from 1.3 million square kilometres of land (roughly 15.8% of the entire continent).
Lying 16m below sea level and draining such a huge area, it is one of the largest internal drainage systems on Earth.
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Why is there so much salt? Over the past 600 or so million years, much of the rock making up the Lake Eyre drainage basin is sedimentary, having been formed on the bed of oceans. These rocks are composed of sand, mud and pebbles and also include much marine salt. Uplifted into mountain ranges, erosion breaks down the rock and frees the salts which flow with the water either back to the sea or in the case of these internal rivers, run into Lake Eyre.
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| Right: This lake, part of a tributary of the Flinke River at 'Curtin Springs' on the Lassetter Highway has been graded with a road grader to harvest the salt.
With no refrigeration. 'Curtin Springs' cattle station had to salt down its beef before trucking it to Alice Springs.
Below: Crystalline salt on the salt lake surface after being graded. The crust is reforming and there is some surface water.
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| Periods of rain are followed by long periods of hot dry weather which evaporate the water, leaving the salt behind. Salt also comes from the breakdown of volcanic rocks formed from upwellings of magma or lava from below the crust.
Evaporation from most inland salt lakes exceeds 2000mm per year, so they very quickly become a crust over great depths of bluish, slimy, salty mud that, because of the salt , stays saturated.
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| Left: Napperly Lake, out from the West Macdonnells NT shows a number of high water marks.
Typical of these lakes, the swales of red dunes become outwash areas from mountains and overflow areas from rivers become large areas of islands, bays and peninsulas, all presenting a real maze for explorers to attempt a crossing.
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| The vast extent of Lake Eyre. The land in the middle distance is an ancient body of salty sand. In it will be masses of crystallised gypsum, creating a very soft, puffy surface. The low vegetation is mainly saltbush and other salt loving plants: pigface and other succulents. Note the old higher shorelines of drift material and no trees in the picture.
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Below: Another side of salt lakes - following periods of rain. Most first impressions are of wide areas of low lands. Here, Lake Torrens in SA is set among acacia covered dunes. When this was taken there had been heavy rains in the Flinders Ranges filling the wide shallow basin with about 0.5m of very saline water. The beaches are of glistening white salt crystals. The saline waters produce countless brine shrimps that are then fed upon by great flocks of water birds. Stilts then nest in tens of thousands on some sandy islands surrounded by an endless food supply until the waters evaporate.
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| | The edge of Lake Eyre South after a storm that partially filled the lake with 10cm of water. Again, brine shrimps and other invertebrates boomed causing a shift in bird populations. Here, at sunrine are Stilts wading the shallows along with Black Ducks. When water reaches the lakes, along with the Murray-Darling system, these areas become the 'duck hatchery' of Australia.
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Left: River Red Gums here growing on hypersaline ground. This ability of the River Gum to survive on such high salt soil has been used in Israel to drain or dry out saline swamps in desert areas.
Below: A not so salty lake in Western Australia, showing the typical scrubby vegetation around its foreshores. These are very stubby melaleucas. These WA lakes have a large number of melaleuca species adapted to the foreshore habitat.
Text and images from Allan Fox March 2009.
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