The modern course of the Murray River was carved 70,000 years ago when a series of earthquakes and aftershocks that went for years lifted the ground along a fault line in southern NSW.
It was an event local Dreaming says was the rainbow serpent’s tail flicking.
The 80-kilometre Cadell fault line stretches from Deniliquin through Echuca, to Rochester in northern Victoria.
GeoScience Australia earthquake geologist Daniel Clark said the release of energy from that ancient event was 30 times that seen in the Victorian earthquake last week.
“The Riverine plain is a fairly flat space normally and 70,000 years ago the Murray River carried on happily westward through Mathoura,” Dr Clark said.
“A series of six very large earthquakes events formed the fault scar, which is up to 10 to 15 metres high at Mathoura.”
He said studies piecing together the history of the tectonic jigsaw indicates the earthquakes occurred every 5,000 to 10,000 years, ultimately diverting the Murray through Echuca.
“The really interesting thing about his process is that there was a lot of partial damming and ponding involved in this earthquake activity so the Barmah Forest, the largest red gum forest in Australia, formed as a result of this tectonic activity.”
Mick Barlow from Moama said the impact on the landscape could be seen while driving between Mathoura and Deniliquin, as the highway was on the uplifted land.
“As you are driving along the Cobb Highway and look out to the east, you’ll find the tree level is below your eyesight,” he said.
“You can see this escarpment along the edge of the Gulpa Creek.
“It has provided us with a slope of land west of the Cadell Fault where natural irrigation was easy to set up once the water was lifted out of the river.”
Dreaming tells of serpent tail flicking
Chief executive of the Yorta Yorta Nation Aboriginal Corporation Monica Morgan said the creation of Dhungula, or the Murray River, is told through Dreaming stories.
“The rainbow serpent was called back and the curves and bends that we know as Dhungula came back and during that process flicked their tail,” Ms Morgan said.
“The flicking of the tail created a new vibration in the country which caused the change in that particular part of the river area.
“The story also goes that after about 25,000 years there was a call by our mob to all the Nations because there was a build-up of all the water to the north.
“So our story is that our mobs all got together and over a period of time created a channel which released some of the water.
“Another flick of the tail around 8,000 years ago and the water then turned back south.”
She said there was a special connection to the forest and wetlands.
“It is, and was, always a food bowl for Yorta Yorta people and our clans and mobs from around the area.
“We have great big ceremonial grounds that people would come to from hundreds of miles away and share with us around the season.”
Fault dormant for thousands of years
Daniel Clark, earthquake geologist with GeoScience Australia, said while there were thousands of fault lines across the country, we only know of a few hundred that are active and producing earthquakes now.
“A fault is a line of weakness within the earth’s crust, it doesn’t necessarily mean that it is seismically active but earthquakes happen on fault lines,” he said.
“We would consider the [Cadell] Fault to be dormant because it hasn’t had one of these earthquakes for the last 20,000 years but that does not mean that we can forget about it.
“Critical infrastructure like dams, power stations and hospitals certainly have to take into account these large events.
“For instance, the Hume Dam would be built to withstand a one-in-10,000-year recurrence earthquake event, which is at the sort of frequency that the Cadell Fault would generate.”Internet Explorer Channel Network