In today’s Academic Minute, Dr. Tom Coulthard of the University of Hull reveals the presence of ancient rivers that flowed across the Sahara Desert.
Tom Coulthard is a professor of physical geography at the University of Hull. His diverse research interests include modeling the impacts of environmental change, metal contamination in river systems, and the impacts of vegetation on fluvial geomorphology. He holds a Ph.D. from the University of Leeds.
More about Dr. Coulthard's modeling of fluvial geomorphology can be found at http://www.coulthard.org.uk/.
Dr. Tom Coulthard - Ancient Rivers in the Sahara
125 000 years ago the earth was much warmer - and our climate was quite different. In particular North Africa was much wetter because the zone of wet weather north of the equator - called the monsoon - was 600km further north. Parts of the North Africa that are now desert were green and fertile though the main belt of the Sahara desert was still extremely dry. But, this wetter weather meant that mountains to the south of the Sahara desert received reasonable amounts of rainfall - whereas today they are very dry. Previous researchers have suggested that water falling on these mountains could have created large rivers - that would have flowed across the Sahara - pushing through over 1000km of desert from these mountains to the coast of the Mediterranean.
This is important, as 125 000 years ago was when archaeologists believe that humans - our ancestors - were migrating out of Africa and into Europe. They may have moved along the Nile, the Arabian coast or many thousands of kilometers away up the coast of West Africa. But if these rivers were flowing then, there was a more direct route from central Africa to the Mediterranean.
We developed a complex computer model to test this. First, we used a climate model - like those used today to model climate change - to predict how much rainfall was falling over these North African mountains 125 000 years ago. Then we took the rainfall and worked out how much of this sank into the ground, evaporated or flowed over the surface as a river. We then let the model run water over the landscape of North Africa and it re-created three massive rivers flowing across what is now Algeria, Libya and Tunisia.
These three old rivers we re-created were large - together as big as the Nile or the Rhine - and we showed that they were flowing for long enough to create green corridors - lush with vegetation - along which ancient humans could have migrated to the Mediterranean and then into Europe.