Editing Murray River (section)

== Ancient history ==

===Lake Bungunnia===
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Between 2.5 and 0.5 million years ago, the Murray terminated in a vast freshwater lake – Lake Bungunnia – formed by earth movements that blocked the river near [[Swan Reach, South Australia|Swan Reach]]. At its maximum extent, Lake Bungunnia covered {{convert|33000|km2|sqmi|0|abbr=on}}, extending to near the [[Menindee Lakes]] in the north and to near [[Boundary Bend]] in the south.<ref>{{cite web|title=Murray River's natural history dates back 130 million years|url=http://www.murrayriver.com.au/about-the-murray/how-the-murray-river-was-formed/|work=The Murray River is an ancient river, even by the time scale of geologists. Its origins date back about 130 million years ago.|publisher=Discover Murray River|access-date=12 December 2013}}</ref> The draining of Lake Bungunnia occurred approximately 600,000 years ago.<ref>Rogers, P.A. (1995): Continental sediments of the Murray Basin. '''In:''' Drexel, J.F. & Preiss, W.V. (Eds.) The geology of South Australia. Vol.2, The Phanerozoic. p. 252. ''South Australia Geological Survey, Bulletin 54''. {{ISBN|0-7308-0621-9}}</ref>

Deep clays deposited by the lake are evident in cliffs around Chowilla in South Australia. Considerably higher rainfall would have been required to keep such a lake full; the draining of Lake Bungunnia appears to have marked the end of a wet phase in the history of the Murray–Darling Basin and the onset of widespread arid conditions similar to today. A species of ''Neoceratodus'' [[Queensland Lungfish|lungfish]] existed in Lake Bungunnia;<ref>{{cite book  | year = 1990 | title = The Murray | editor1-last= Mackay |editor1-first = Norman | editor2-first = David | editor2-last=Eastburn| publisher = Murray–Darling Basin Commission | location = Canberra | isbn = 1-875209-05-0}}</ref> today ''Neoceratodus'' lungfish are only found in several [[Queensland]] rivers.

=== Cadell Fault and formation of the Barmah red gum forests ===
{{main|Cadell Fault}}
The noted Barmah River red gum forests owe their existence to the Cadell Fault. About 25,000 years ago, displacement occurred along this fault, raising its eastern edge, which runs north–south, {{convert|8|to|12|m|ft|0|abbr=on}} above the floodplain. This created a complex series of events. A section of the original Murray River channel immediately behind the fault was rendered abandoned (it exists today as an empty channel known as Green Gully). The Goulburn River was dammed by the southern end of the fault to create a natural lake.

The Murray River flowed to the north around the Cadell Fault, creating the channel of the [[Edward River]] which exists today and through which much of the Murray's waters still flow. Then the natural dam on the Goulburn River failed, the lake drained, and the Murray changed its course to the south and started to flow through the smaller Goulburn River channel, creating "The Barmah Choke" and "The Narrows" (where the river channel is unusually narrow), before entering into the proper Murray River channel again.

The primary result of the Cadell Fault – that the west-flowing water of the Murray River strikes the north–south fault and diverts both north and south around the fault in the two main channels (Edward and ancestral Goulburn) in addition to a fan of small streams, and regularly floods a large amount of low-lying country in the area. These conditions are perfect for [[Eucalyptus camaldulensis|River Red Gums]], which rapidly formed forests in the area. Thus the displacement of the Cadell Fault 25,000 BP led directly to the formation of the famous Barmah River Red Gum Forests.

The Barmah Choke and The Narrows restrict the amount of water that can travel down this part of the Murray. In times of flood and high irrigation flows the majority of the water, in addition to flooding the Red Gum forests, actually travels through the Edward River channel. The Murray has not had enough flow power to naturally enlarge The Barmah Choke and The Narrows to increase the amount of water they can carry.

The Cadell Fault is quite noticeable as a continuous, low, earthen embankment as one drives into Barmah from the west, although to the untrained eye it may appear man-made.
[[File:Confluence of Murray & Darling Rivers, Wentworth, NSW, 9.7.2007.jpg|thumb|center|750px|The [[confluence]] of the [[Darling River|Darling]] and Murray Rivers at [[Wentworth, New South Wales]]]]