The world's largest desert harbored one of the world's largest river systems as recently as 5,000 years ago, but it has since dried up and been buried in sand, reports the Guardian.

A French-led team of researchers discovered the vast river system, which stretches for hundreds of miles beneath the parched desert, by making use of radar images taken from a Japanese Earth observation satellite. The images show how the concealed river beds align almost perfectly with a huge underwater canyon that extends off the coast of Mauritania into waters more than three kilometers deep.

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Ever since researchers discovered fine-grained, river-borne particles at the bottom of this underwater canyon, they have speculated about the existence of a once-powerful river that must have fed into it. But today, the geography of Mauritania, a country largely defined by sandy desert or semi-desert, seems like an unlikely place for such a massive waterway.

Researchers followed their hunch, however, and it paid off. The proposed Tamanrasett River would have flowed from sources in the southern Atlas Mountains and Hoggar highlands in what is now Algeria. It likely flowed as recently as 5,000 years ago, until the encroaching Sahara Desert eventually engulfed it in sand. If we could go back in time, the entire region would have seemed transformed. It would have provided plentiful resources for wildlife, vegetation and for the people who lived there.

"It’s a great geological detective story and it confirms more directly what we had expected. This is more compelling evidence that in the past there was a very big river system feeding into this canyon," said Russell Wynn, from the National Oceanography Center in Southampton. "It tells us that as recently as five to six thousand years ago, the Sahara desert was a very vibrant, active river system."

Though the Sahara stretches over an area roughly comparable to the size of the United States, its only major waterways exist on its borders: the mighty Nile to the east, and the Niger and Senegal rivers in the south and southwest. The Tamanrasett River would have been a massive waterway right through the heart of the thirsty Western Sahara. If it still flowed today, it would represent the 12th largest river system on Earth.

It may be hard to believe that such a huge waterway could have disappeared completely in just a few thousand years, but it goes to show how rapidly climate change can transform a landscape.

“People sometimes can’t get their head around climate change and how quickly it happens. Here’s an example where within just a couple of thousand years, the Sahara went from being wet and humid, with lots of sediment being transported into the canyon, to something that’s arid and dry,” Wynn said.