Sand accumulation and groundwater in the eastern Sahara

Abstract

Nearly all sand dune fields in the eastern Sahara are located within topographic depressions. The sand, mostly composed of quartz grains, occurs south of limestone plateaus that border the Mediterranean seacoast, over which the wind blows southward. The source of the sand is the "Nubian Sandstone," which is exposed throughout the southern part of the eastern Sahara. Satellite images, particularly radar data, reveal that sand-covered, northward-trending courses of dry rivers end at the depressions. The sand appears to have been deposited, most likely in lake beds, during wet climates. Alternating dry climatic episodes resulted in sculpturing these deposits into sand dunes and sheets by southward flowing wind. The depressions must have hosted great volumes of surface water during the wet climates. Much of that water would have seeped into the underlying rock through primary and/or secondary porosity. It follows that areas of large accumulations of sand may host vast groundwater resources.