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Core samples confirm Murray River was once a giant lake

 

Three researchers from the University of Sydney and the University of Newcastle have concluded Australia’s Murray-Darling river was a lake more than 5000 years ago.

As one of Australia’s most iconic natural wonders, the Murray River has not always looked like it does now.

The sediment core collected by the researchers. Image courtesy of Anna Helfensdorfer.

The existence of a lake has been confirmed by a team of researchers who discovered the ancient lake stretched approximately 200km upstream from the Murray Mouth to an area near Swan Reach, in Victoria’s east Gippsland region.

Researchers Hannah Power, Anna Helfensdorfer and Tom Hubble published their findings online, showing the lake existed in a period between 4000 and 8500 years ago.

This was during the Holocene highstand, where sea levels rose to 120 metres above what is seen today and was due to melting ice from the Earth’s last glacial period 18,000 years ago.

The discovery was made using high resolution two- and three-dimensional modelling which mapped water levels and flows in the area.

A 30-metre-long sediment core was also drilled from the Lower Murray River’s floodplain, with each layer believed to show increased or decreased river flow. It is estimated that each metre of sediment took roughly 315 years to form. The sediment on the floodplain is composed of clay and silt that was washed downstream in at least the past 4000 years.

In the past 5000 years as sea levels began to drop to where they are today, the lake dried up and returned to a river.

According to the research team, the new discovery can indicate how the river system will be affected by future sea level rises in the future, along with a more accurate collection of past floods and drought records to help manage water in the Murray.

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