posted
Old story from 2007 but this is the first I have heard of it.
The discovery of a massive ancient lake in Darfur could help explain how the world’s biggest groundwater reservoir came to be under one of the driest parts of the planet. It is also indisputable evidence that the Sahara was once a wet, green region, researchers claim.
Eman Ghoneim at the Boston University Center for Remote Sensing in Massachusetts, US, was using satellite imagery to study the ancient hydrology of north-western Sudan when she noticed a dark, 250-kilometre-long segment on the radar images.
The discovery came as a complete surprise, Ghoneim says. The radar waves penetrate through the sand that covers the region, revealing the structure of the substrate below. Ghoneim says the line was very dark, contrasting with the bright white of the surrounding solid rock, and 1 kilometre wide. The dark colour is typical of a mixture of gravel and sand, suggesting there was an ancient shoreline buried underneath the sand.
This was confirmed by other lines that intersected the main segment, representing the rivers that once supplied the lake in water. “There were nine tributaries in total,” says Ghoneim. “Three were major rivers.”
“Also, in one section, there was not one shoreline but four next to each other,” she adds. “This gives us an idea that at one point the lake began to shrink.”
High volume Having identified the shoreline, Ghoneim integrated the radar images into data from the Shuttle Radar Topography Mission, which records geological elevations. This enabled her to outline and model the entire lake (see image, right).
The topography data (bottom right) revealed that the shoreline outlines a large depression and that, at its largest, the lake covered an area of about 30,750 square kilometres and contained about 2,530 cubic kilometres of water – more than five times the volume of Lake Erie in North America. The Lake’s surface would have been larger than Massachusetts, US.
The researchers plan to return to the area for fieldwork to determine the exact age of the lake; though Ghoneim says they know it is “definitely a pre-Holocene lake”, which would make it over 11,000 years old. It is known that the region has been dry since the Holocene.
Water strike “One thing is certain: much of the lake’s water would have seeped through the sandstone substrate to accumulate as groundwater,” says Farouk El-Baz, director of the Center for Remote Sensing.
Indeed, the ancient lake lies over what is now the world’s largest groundwater reservoir. It was discovered in 1953, when efforts to find oil in Libya came across water instead. Since then, several projects have been set up to mine this millennia-old water. The aquifer now supplies agriculture in the region.
The reservoir, which is several hundred metres underneath the surface of the Sahara in a large region shared between Egypt, Libya, Chad and Sudan, contains roughly 150,000 cubic kilometres of water. The water is held there by porous Nubian sandstone.
“The ancient lake helped feed part of the Nubian groundwater aquifer,” says Ghoneim, adding that “ancient rivers, such as the paleo-rivers under the Selima Sand Sheet in south west Egypt and the Kufra paleo-river in eastern Libya, also contributed greatly.”
-------------------- It's not my burden to disabuse the ignorant of their wrong opinions Posts: 2707 | From: New York | Registered: Jun 2015
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posted
What are the archaeological findings in the region, or nearby?
Posts: 22235 | From: האם אינכם כילדי הכרית אלי בני ישראל | Registered: Nov 2010
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