Document Type

Article

Publication Date

2001

Abstract

The Eastern Sahara 18 presently the driest place on Earth. However, there iS geographical, geological, and archacological evidence OF wetter climates a in the past. Its dune fields are largely enclosed in topographic depressions that served as terminal points for a number of palaeo-rivers and streams. In some of these channels, moisture from occasional rainfall, or from leak- ing fractures tapping deeper confined aquifers, has been detected at 25 cm beneath the surface. Radar images are used here to map the distribution and morphology of the channels North of the Gilf Kebir plateau and beneath the Great Selima Sand Sheet. Radar waves have the unique ability to pen- etrate up to 2 m bencath dry, fine-grained desert sand to reveal subsurface features. It is believed that fluvial episodes in the Eastern Sahara are closely linked to the vast accumulations of sand, including: a) the Great Sand Sea, where major channels lead from the Gilf Kebir plateau Northward toward lower topography; and b) the Great Sclima Sand Shect, where four major drainage lines cross T or lead to its borders. The convergence of the channels suggests that surface water occupied inland depressions. Some of that water would have seeped into the und derlying porous sandstone to accumu- late as ground water beneath both the Great Sand Sea and the Great Selima Sand Sheet.

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