Document Type

Article

Publication Date

2007

Abstract

The first Shuttle lmaging Radar (SIR-A) instrument was flown in earth orbit in November 1981. Data were obtained pertaining to a flat, sand-covered region in the eastern Sahara of North Africa. These data revealed courses of three channels or dry river courses varying in width from 8 to 20 km. This revelation increased interest in the geomorphology of desert regions and implications thereof to the geoarchaeology of prehistoric environments, particularly in southwestern Egypt. For radar waves to penetrate desert sands and reveal the underlying topog- raphy, the surface material must be dry and fine grained. Moisture reflects radar waves and interferes with their penetration ability, and the size of sand grains has to be less than one-fifth of the wavelength of the radar waves. These two conditions are satisfied in the eastern Sahara. More data obtained by SIR-C and Radarsat conlirm these findings. Identification of the dry river courses explains the prevalence of prehis- toric wet conditions, which allowed the existence of plants, animals, and man throughout the eastern Sahara. It also xplains the underlying reasons for the location of oases in this hyper-arid region. The eastern Sahara must have been supplied by water through the ancient rivers, from occasional rainfall, even after their courses were buried by wind-blown sand. The analysis of unveiled river courses shows that they originate from highland massifs in the Sahara or from the sub-Saharan belt of the Sahel. The latest time water flowed in these courses was during the last pluvial, from 11,000 to 5,000 years ago. Alternation of wet and dry episodes brought life and death, respectively, to this region as indicated by human implements as well as flora and fauna of a savanna-like environment. Much of the watet that lowed in these rivers must have seeped into the substrate to be stored as groundwater This would have occurred along fractures n the host rock or through the rock's primary porosity, especially in areas that were water rich such as beneath the r numerous inland lakes that persisted during a humid periods: Ample proofof this phenomnenon is provided by the high produc tivity S the "Nubian" groundwater aquifer in the eastern Sahara. Thus, a detailed knowledge S the geomorphology of t the desert allows uS to understand better its archaeological record as well as its groundwater resources.

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