A network of ancient rivers and streams that once flowed beneath Australia's Simpson desert – famed for its dune fields – has been mapped in a new study. The map could lead the way to valuable minerals and water resources in this drying continent.

Michael Hutchinson and John Stein of the Australian National University in Canberra extracted data from previous ground surveys to map an ancient river system 35 metres below the surface of the desert. They think the channels are among the world's oldest at 50 million years old, when the now barren land would have been lush and well watered.
[The dead rivers are a reminder of the great climate changes that have taken place in the continent, says Robert Craddock of the Smithsonian Institute in Washington, a co-author on the paper.

Data mining
Thanks to data from remote sensing satellites, mapping buried waterways has become fairly commonplace worldwide. But Hutchinson says the Simpson desert rivers are too deep to detect using standard satellite techniques. And the massive sand dunes, towering up to 20 metres high and hundreds of kilometres in length, interfere with this kind of analysis.

So the team took ground surveys of the desert's surface contours and used software developed by Hutchinson to join all the lower points on the map to devise a complete river system. To remove the distortions caused by the sand dunes – which appeared just 1 million years ago, long after the ancient river channels formed – the team used only points between the dunes to give an accurate picture of the underlying topography.

"We removed the data recorded over the sand dunes," says Hutchinson, and the final results "looked sensible". "They naturally connect with the current streams of the Simpson desert, and they are all draining toward the lowest point in the landscape," he says.

The ancient waterways of the Simpson are still influencing the landscape, says Craddock. They provide pathways for groundwater, so dictating the location of desert lakes. The map may also aid petroleum and mineral exploration, he adds, because the location of deposits is associated with underground streams.

Too deep
Because there is no way to detect directly water systems this far underground, the results cannot be validated, says Hutchinson. But despite this, James Bowler of the University of Melbourne believes the methodology is "very accurate".

"The data is telling us a whole new story about the ancient face of the land often obscured by the Simpson desert dunes, and this is a very powerful tool," he says. "It's going to give us a tremendous amount of applied value in terms of mining and groundwater."

But Elisabeth Bui, an expert in environmental modelling of earth surfaces at CSIRO Land and Water in Canberra, doubts the practical usefulness of this study. "I doubt that there is heaps of underground water stored in these palaeochannels in the Simpson desert," she says.