The drainage pathway of the River Nile has persisted over the past 30 million years, because a conveyor-belt-like motion, or ‘convection cell’, in the Earth’s mantle has stabilized surface topography according to a paper published in Nature Geoscience.
Drainage systems of large rivers have long been a puzzle, and two competing possibilities were suggested for the evolution of the River Nile. In one scenario, river flow from Ethiopia to the Mediterranean has been active for the past 30 million years. Alternatively, drainage pathways at that early time led from Ethiopia westward towards the Congo Basin or northwestward towards the Sirte basin, and a connection to the Mediterranean was established much later, about 5 to 8 million years ago.
Claudio Faccenna and colleagues present geological and geophysical evidence as well as simulations with a geodynamical model that suggest an early establishment of present-day drainage pathways. They find that since about 30 million years ago, a convection cell has operated in the Earth’s mantle, with upwelling and topographic rise beneath Ethiopia and downwelling associated with sinking under the eastern Mediterranean Sea, which led to the current drainage pattern.