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Gorges and/or Canyons
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Allan Fox, principal author of Wild Habitats, talks about the wide range of ecosystems that have evolved in Australia’s gorges - which are also known as canyons. Gorges and/or canyons are found in mountainous country. Apart from a few places where mountainous sandhills are found, the cores of all mountains are of rock that has been raised by massive, long term, but very slow uplifting movements. Sometimes the vast pressures required are exerted at the edges or, if the rock is deep below the surface, it is hot and plastic. In these cases, the rock is folded in huge ripples. During the convulsions caused by the pressure, much of the rock is uplifted to form chains of mountain ridges or, if all the pressure is from below, then great flat areas of country might be lifted to become plateaus or tablelands. Now, if the rock is hard when it is uplifted, it will probably also crack and fracture, forming faults. These faults become the places where water from the weather, running off the highland will follow. This water movement removes rock broken during the uplift or rock being rotted and weathered. This erosion will ultimately open up the fault, widening it into a steep-walled valley, the gorge or canyon.
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| This great cleft in the north Flinders Ranges was caused during the warping and uplifting of the Gammon Range section.
It holds water in pools long into drought because the sun never penetrates there and provides water for Australia’s most beautiful mammal, the yellow footed or ring-tailed Rock Wallaby.
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Below: Wet season waterfalls of upper Jim Jim Creek, roaring from clefts in the horizontal sandstone of the ancient (1.7 billion years) Arnhem Plateau. Over time, as the water widens the rifts, the walls will retreat, lengthening the Jim Jim Gorge, Kakadu. | | Numerous bats live in the water-worn caverns as well as Australia’s largest snake, the Oenpelli Python. The tiny Narbalek Wallaby finds shelter on its walls. The massive power of the falling water cuts a very large and deep plunge pool below the falls. The sandy debris is carried out into Van Diemen Gulf to enlarge the delta there and, consequently, the coastal plain.
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In The Pilbara, for instance, the wet season produces masses of rain which gushes through the gorges and over waterfalls, eroding the rocks on its way. The water also undercuts cliffs and, if sandstone, whole cliff walls can collapse, forming gorges. Limestone rocks are not only affected by water but by the chemicals in it which cause further erosion. It is not surprising then that there are many caves and holes in limestone rocks. When the roof of the cave eventually collapses, gorges are left. The Windjana Gorge in Western Australia was formed when the rivers cut through the 500 million year old coral reef, leaving a beautiful cross section. It has a steep front, a reef flat on top and a gentle, tapering slope off the back and, amazingly, visitors can walk straight through it.
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Below: Chambers Gorge in the North Flinders Ranges shows what the streambed of a typical gorge is like, full of boulders, pebbles or gravel, the residue from the breakdown of the sides of the gorge. The white staining on the stream boulder is of salt and calcium. The salt will finally come to rest in Lake Frome, a very large salt lake. But the brackish water sustains a large number of animals – birds, rock wallabies and Euros. |
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The Fitzroy Gorge in Fossil Downs is another good example. More water flows down the Fitzroy River than all of Australia’s other rivers combined, creating violent torrents of water in the wet season. There have been numerous threats to build dams on the Fitzroy River and on one memorable media moment, when an ABC film crew filmed campaigning canoeists, one film crew member sustained a broken leg while another suffered a broken arm. The sheer walls, ledges and terraces of gorges make safe habitats for animals like rock wallabies. The rabbit-sized monjon, which is the smallest of the rock wallabies, in the King George Gorge negotiates the narrow ledges and cracks easily. In the more broken, sloping areas of gorges, wallaroos known as Euros or Hill kangaroos, hop vertically around the rocks in their quest for Spinifex and other shrubs.
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| Part of a vast flock of Little Corellas, attracted to Chambers Gorge during the 1983 drought by the water.
They ‘camp’ in the River Red Gums overnight and like many cockatoos can be vandals, tearing apart their camp trees.
The rest of the flock was camped on the ground under the sparse shelter of Bluebush having destroyed most of the timber shelter.
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One of the advantages of gorge habitats is that they are not favoured by feral cats or foxes so these animals have only one major predator, the wedge-tailed eagle. The red cabbage tree palm is another indication that gorges are safe havens, reminders of a more lush environmental past. Palm Valley in Central Australia is a remnant of the rainforest that once covered the area and the trees that survive there do so in the damp, cool places of gorges. Growing with them are large cycads. Kings Canyon in the central Australia is home to a very beautiful guinea flower as well as grevilleas and cycads. Snakes also frequent gorges. Australia’s largest, the Oenpelli python which was only “discovered” in the 1970s, lives in gorges on the Arnhem Land Plateau. It, like the other animals that frequent these rocky habitats, uses camouflage to great effect, its mottled brown patterns blending into the sandstone. Frogs live in these gorge habitats too. There are a number of small frogs in the cool areas around the water and under rocks as well as green tree frogs and a great richness and diversity of invertebrates that are food for many gorge dwellers. There are often water rats as well, highlighting the great diversity of these ecosystems.
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Below: More ranges of heat-hardened quartzite, the West Macdonnells showing the grand Ormiston Gorge, formed where a major arm of the Finke River cut its way through the much fractured mountains. |
| Ground cover on the tops is mainly Spinifex hummocks interspersed with red-flowering grevillea. Towards sun-up and sunset, troops of the exquisite Spinifex Pigeons march down to the water to drink beside the Black-flanked Rock Wallabies. High above, the Wedge-tailed Eagles, soar in sublime arcs. River Red Gums grace the waterholes.
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Gorges also have a diverse set of microclimates, caused by the temperature range of areas that maybe exposed and hot to densely shaded and cool. Carnarvon Gorge in Central Queensland with its 800 metre high sandstone walls is one such case. The sandstone was topped by the volcanic rock basalt. Eroded pieces falling into the gorge have been rolled around by the flooding river, eventually forming hard boulders. The water is trapped in many pools, making a great habitat for platypus. By the damp banks are vestiges of rainforest with palms and vines, along with spotted gum and eucalypts. Up on the base of the cliff it is much drier, so the eucalypts there are more like woodland ones. In the MacDonnell Ranges near Alice Springs there is plenty of evidence of how water formed the gaps in the quartzite rock. Some waterholes like Ellery’s Gap are ten metres deep and dangerous as the water past the first half metre is very cold.
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Below: River Red Gums by the deep, permanent water hole tucked into the Big Bend of Ormiston Creek, a tributary of the Finke River, afford many nesting holes for Galahs, Little Corellas and Pink Cockatoos. The cliffs of the tiers of terraces up the 1000 metre sides carry masses of huge tumbled boulders under which Euros and Rock Wallabies shelter. |
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For the Aborigines it was the gorges that became their dry period camp sites, where they could move between gorges as best suited the seasons, and food availability. Thus they were not really nomadic, since their movement tended to be among their known sites all of which would be located on their particular part of country. Gorges are a unique ecosystem and their stunning beauty makes them ideal tourist attractions.
They are obviously attractive to the flora and fauna that inhabit them.
Images from Allan Fox
Text: Allan Fox and V.B. November 2009
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