Satellite traces ancient riverbeds buried in the Sahara

Ars Technica : The precession of Earth’s magnetic pole is known to have shifted atmospheric patterns enough that at various points in the past rain was common in the area that is now the Sahara desert. A variety of evidence has pointed to the existence of a river that emptied off Africa’s western coast in what is now Mauritania. Seafloor sediments there contain deposits of material similar to that found at the end of the Nile, and seafloor surveys found a submarine canyon similar to ones at other river mouths. Topography mapping provided hints to the river’s path on land, but the Sahara’s sands cover most of the direct evidence. Charlotte Skonieczny of the French Research Institute for Exploitation of the Sea and her colleagues turned to satellite imagery to find that evidence. Microwave radar aboard Japan’s Advanced Land Observing Satellite can see through a few feet of sand. With it, the researchers were able to trace the river valleys more than 500 km inland before the sand became too deep to penetrate.