Australia: The Land Where Time Began

A biography of the Australian continent 

Finke River

The Finke River, Larapinta to the local Aborigines, which passes to the west and south of Alice Springs, is one of the oldest rivers in the world. Ellery Creek is a tributary of the Finke. 

The Finke originates on the Arunta Block, about 75 km west of Alice Springs and more than 350 km northwest of the township of Finke. It cuts through a series of east-west ridges and ranges. It continues south into the duricrust plains and sand-ridge deserts on its way to Lake Eyre. It sinks into sand dunes on the edge of  the Simpson Desert. It has cut spectacular gorges through the Macdonnell Ranges, Krichauff Range, and James Range, where it has cut deeply into bedrock. It has cut 2 gorges north of the James Range, the unused palaeogorge being dated to the Miocene. The climate is thought to have been subtropical when the unused gorge was cut. The Finke is ephemeral and so flows only after heavy rain. At these times it carries a heavy sand load. Some of the sediment is deposited in eddies and backwaters, these being called slack-water deposits. Some of these have been dated  which allows a record of previous floods to be recorded.

The slack-water deposits in the Finke Gorge are the best sequence discovered in Australia. These deposits record 7 major floods, all  in the past 850 years, leading to the conclusion that there has been a marked increase in the frequency of extraordinary floods in the Late Holocene and that the river flow is marked by extreme variability.

Most rainfall occurring in the ranges that flows down the Finke is insufficient to reach far across the plains. After these events the water is quickly lost to the dry river bed and to evaporation as the river crosses the Missionary Plain. When large floods occur, as they need to be to reach along the length of the river, they can change the morphology of the channel, and because of the rarity of these events the changes can be long-lasting.

In 1967 Tropical Storm Gwen dumped 150 mm in 11 hours on the headwaters of the Finke. The river spread out when it emerged from the valleys of the ranges to cover an area 0.8 m deep and 11 km wide. When it flowed down shallow gradient of the south-sloping flat country between the longitudinal dunes of the Simpson Desert it dived into several streams. In some of these interdune flood-outs it reached a depth of 6 m and took 19 months to be totally absorbed and evaporated. This was the biggest flood since 1895, when the Hermansburg Mission recorded 240 mm in a single mid-January event. Larger floods occurred in 1971, 1974, and 1988, the largest concentration of floods in historical records.

The Finke passes through all the typical desert environments in Australia. Arising in the Macdonnell Ranges and James Range, it passes through mulga shrublands, spinifex sandplains, gibber plains, mesas, salt lakes and red sand dunes, and disappears into the sand of the Simpson Desert.

A record of the changing climate of the western Simpson Desert in the late Quaternary has been found in sediments near the Finke township. Here the deposition of the Finke Valley alluvium has been dated to about 90,000 BP. After this time there was a break in the deposition until the Holocene. The Early- to Mid-Holocene activity is thought to be the result of the reactivation of the northern monsoon that had stopped during he last glacial phase of the Pleistocene Ice Age. This activation of the monsoon is not recorded in the rivers of the eastern part of the Lake Eyre Basin. It is thought the monsoon was not recorded here because of the lower energy and responsiveness of the drainages.

It is believed the Finke has probably followed at least part of its present course since the Devonian and Carboniferous, during the Alice Springs Orogeny, from 380-280 Ma, resulting in major faulting, folding and uplift across much of central Australia.

There are some relict 100 million-year-old Cretaceous surface rocks on the tops of some parts of the Macdonnell Ranges, but most of the crests are Miocene duricrust. This means that the rivers that cut across the grain of the ranges, such as the Finke, is at least 20 million years old. 

Sources & Further reading

Mary E White, Running Down, Water in a Changing Land, Kangaroo Press, 2000

Links

Finke River (Larapinta)

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Last updated 22/05/2011

 

 

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading