Eman Ghoneim of the Boston University Center for Remote Sensing in Massachusetts was using radar satellite imagery taken of the northwestern Sudan to map ancient hydrology when she discovered evidence that an enormous lake once existed in the region—a sharp contrast to the very arid, parched environment that exists there today. This discovery confirmed that the climate in this part of the Sahara was once humid enough to support a green region with ample water and vegetation. Because radar waves have the capability to sense beneath the ground's surface, they were able to differentiate the subsurface layers and image them. What the radar revealed was a dark area roughly 0.6 miles (1 km) wide, in direct contrast to the bright spectral signatures of the sand around it. The low (dark) signature was caused by a mixture of sand and gravel, indicative of a shoreline from a long-gone ancient lake. In addition, Ghoneim identified nine lines that radiated from the shoreline, showing where rivers once drained into the ancient lake.
Further research confirmed that there was not just one shoreline, but four. This was important information because it told researchers that at one time the area had ample moisture and that the lake was fed by tributaries. Then, the supply of water began to lessen, and the lake began to shrink. At each subsequent shoreline, the lake spent some time in equilibrium until climatic conditions turned drier and caused the lake to shrink further. By dating these different shorelines, the area's climate history could be recreated and studied.
Ghoneim was able to combine the radar images with data from the Shuttle Radar Topography Mission (which provided landform elevation data) and create a model of the size of the lake. She determined the paleolake was pre-Holocene in age (older than 11,000 years) and was more than five times larger than Lake Erie.
Through further investigation, scientists have discovered that the water probably seeped through the sandstone beneath it and is now stored in deep groundwater reservoirs. Further proof of this comes from the fact that in 1953, Libya discovered underground reservoirs of water. This precious natural resource represents an important find for an area that will be hit extremely hard by global warming.
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