Farouk El-Baz

Document Type

Article

Publication Date

1979

Abstract

The Eastemn Sahara of North Africa includes most of the land area of Egypt, Sudan, Libya and Chad For example, the extremely dry part of Fgypt to the west of the Nile River occupies two-thirds its land area. hroughout the latter, the flatness of the tcrrain is interrupted by depressions, most of which enclose oases. The rest is a vast plain of vegelation-frec, wind-scoured tcrrain. Because the Eastern Sahara represents the driest expanse of land on Earth, it is replete with evidence of prolonged acolian activities, This ineludes a great variety of sand in the shapc of dunes and sheets. The patterns of sand dunes, coupled with wind data from meteorological satellites, suggest a prolonged history of aeolian transport from north to south in the cast, and westward beyond that. Y et, images from orbiting spacecraft, and topographic data from radar sensinig, show vast arcas where water accumulated as lakes within low topography in the geological past, Radar data also revealed numerous courses of now sand-buried rivers, During wetter climates, water in the paleo-channels tlowed mostly northward Tfhe wet episodes resulted in the erosion of solid rock and the rounding of graias in the turbulent flow af rivers. Sand-sized grains were rounded during water transported and deposited at the botiom of lakes within topographic basins. As the alternatine dry elimatcs prevailed, the sand deposits were shaped into dunes by wind action. Such interactions were revealed at siles throughout the Eastern Sahara, particularly in the Vestern Desert of Egypt. These locations display clear evidlence of repeated intcrplay of fluvial and acolian processes, particularly throughout the Quaterary.

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