Hope for the Sahara
Discovery of ancient mega-lake could mean massive groundwater source
The eastern Sahara Desert might seem like the last place you’d go looking for water. But that’s exactly what researchers at BU’s Center for Remote Sensing (CRS) did, and they found much more than they’d bargained for.
Earlier this year, while using space-based radar to survey prehistoric riverbeds buried beneath the desert sand, Farouk El-Baz, a research professor and CRS director, and Eman Ghoneim, a CRS research assistant professor, discovered the now-dry shoreline of a lake that once was bigger than Massachusetts. The find, in the Sudanese province of Darfur, could indicate the existence of a vast underground water supply for a region stricken by both drought and war.
The first hint of the mega-lake’s existence was a dark, slightly curved line in
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the desert revealed by the sand-penetrating radar and measuring about 48 kilometers long and one kilometer wide.
“At the beginning, we thought this might be a fault line or fracture beneath the surface,” says Ghoneim. But the researchers picked out several more segments of varying length and similar width. As a perimeter began to emerge, they used additional data from the Shuttle Radar Topography Mission to establish that the segments were the same elevation, about 570 meters above sea level, confirming that they formed a shoreline that had disappeared thousands of years ago.
Precisely how long ago the lake existed and when exactly it dried up is a mystery whose solution awaits soil samples and other fieldwork, which El-Baz and Ghoneim hope to do as soon as possible. In the meantime, it is known that the region has been dry for at least 10,000 years.
Before then, the Sahara was a much greener place, at least for certain stretches of time. Ghoneim says the lake — and its river tributaries — may have dried and refilled in cycles over the millennia. “Long periods, hundreds or thousands of years, of wet climate would be followed by a very dry climate,” she says.
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Nevertheless, explains, El-Baz, the water of the ancient lake didn’t simply evaporate. “Much of the lake’s water would have seeped through the sandstone substrate to accumulate as groundwater,” he says.
Consequently, another fieldwork task will be to locate the lake’s center, its deepest point. This would be the most likely spot for drilling to what could be a massive underground supply of fresh water, a precious commodity in a region home to more than 2.5 million refugees fleeing an ongoing civil war in Sudan.
It wouldn’t be the first time space-based data has helped find water beneath the 3.5 million square mile Sahara. In the early 1980s, El-Baz detected a similar ancient lake in the East Uweint basin in southwestern Egypt, where water is as close as 25 meters below the sandy surface. Since then, 500 wells have been dug, irrigating up to 150,000 acres of farmland.
“We hope this new lake will do the same for the Sudanese, and especially for the people of Darfur,” says Ghoneim. An account of their finding will be published in an upcoming issue of the International Journal of Remote Sensing.
Related story: Last spring, Center for Remote Sensing researchers made another find in the Sahara — a 19-mile-wide crater, the biggest ever found in that region.
Chris Berdik can be reached at cberdik@bu.edu.