Ancient Waters, Unique Landscapes

Ancient sands, ancient waters

They include new migrants from the capital of Cairo to the Western Desert in Egypt… urban residents of apartments on Libya’s Mediterranean coast… small communities mainly growing wheat in northern Sudan… and nomadic groups sparsely populating oases in northeast Chad. What do these people have in common?

They all depend on water from the Nubian Sandstone Aquifer System (NSAS), one of the largest and most important underground aquifers of any kind in the world. It is also the world’s largest ‘fossil’ water aquifer system, meaning that the water is very, very old.

The ancient system’s massive reserves, estimated at 375,000 cu km of water (equivalent to about 500 years of Nile River discharge), are confined deep inside the earth’s underground chambers -- staggered, tiered, and pooled beneath the sands of the Sahara Desert, oasis settlements, wadis (dry riverbeds that contain water only during times of heavy rain), small villages, towns, and large cities.

While today there is no definite agreement on the exact age of the NSAS water, new scientific techniques are getting closer. Before, the traditional technique for dating groundwater was through radiocarbon testing, but this had a limit of 40,000 years. A new technique uses the rare isotope called Krypton-81 to trace age. Recently, a team led by professor Neil Sturchio from the University of Illinois in Chicago tested some Nubian samples using the new technique with extraordinary findings. They found that Nubian groundwater is between 210,000 and 1 million years old!

The NSAS as a ‘system’ was created during the Ice Age, also called the Pleistocene epoch, which lasted from 1.8 million to 11,550 years ago. Within this epoch, there were various cold and warm periods, during which time the recharge of groundwater in the NSAS was possible if conditions were wet. Between 5,000 and 7,000 years ago, scientists believe there was some major replenishment through dramatic climate changes.

Today, the NSAS is seen as a closed water system that is only marginally rechargeable. While there is some sparse water recharge from the Nile and precipitation from some areas, the fossil water reserves are largely non-renewable, finite and not an active part of the surrounding hydrological cycle. That means that it can only be pumped out once, like oil. Furthermore, water is not spread evenly throughout the NSAS. In some areas, there is little to no groundwater. In others, there are massive reserves beneath the surface.

The ‘sandstone’ in the system is sedimentary rock formed by the consolidation and compaction of sand and held together by natural cement. Because sandstone can possess up to 35% connected pore space, some call it the most important reservoir rock in the Earth's crust.