Mantle Keeps Ancient Nile on Course

November 12, 2020

If it were not for a hot upwelling of mantle rock in northern Africa, human history may have taken a different course. That’s because without that upwelling, the Nile River almost certainly would have.

For millions of years, the Nile has kept the same steady northward path — an unusual behavior since long-lived rivers generally move over time. Research led by the Jackson School of Geosciences has found that movement of underlying mantle rocks has maintained the Nile’s unique underlying landscape and enabled the river to stay the course. Without the influence of the mantle rocks, the river would have turned west long ago.

The research, published Nov. 11, 2019, in the journal Nature Geoscience, also revealed that the Nile is much older than anyone thought, with the scientists estimating the age of the Nile to be 30 million years — about six times as old as previously thought.

“One of the big questions about the Nile is when it originated and why it has persisted for so long,” said Claudio Faccenna, a professor in the Department of Geological Sciences who led the research. “Our solution is actually quite exciting.”

The results should settle a long-running debate about the age of the river and provide evidence that the slow movement of the deep mantle is one of the key forces shaping our Earth’s landscape and geological processes.

The international research team also included Jackson School scientists Petar Glisovic, who is now a research collaborator at the University of Quebec; and Thorsten Becker, a professor in the department and research scientist at the University of Texas Institute for Geophysics.

In the paper, the researchers connected the tilted nature of the Nile’s topography to a conveyor belt of mantle rock pushing up against the Ethiopian Highlands in the south and pulling the surface down in the north. The research involved studying ancient volcanic rock in the Ethiopian Highlands and correlating it with enormous deposits of river sediment buried under the Nile Delta.

The team verified their findings using computer simulations that re-created 40 million years of Earth’s plate tectonic activity. The model showed the arrival of a hot mantle plume that probably led to the outpouring of lava that formed the Ethiopian Highlands while activating a conveyor belt in the mantle that persists to this day. The simulation reproduced changes in the landscape almost exactly as the scientists had expected — including small details in the landscape such as whitewater rapids found along the length of the Nile. 2020