RECOGNITION OF ANCESTRAL MEGA LAKE IN THE EASTERN SAHARA FROM SPACE DATA

The Great Sahara is among the driest places on Earth. However, during wet phases in the past, when the rain was copious over protracted time periods, the surface was lined by rivers and dotted by lakes. While using Radarsat-1 images to survey prehistoric riverbeds buried beneath the desert sand, several ancient shoreline segments of dark radar signals were observed. Most of these appear as intact linear zones, ~ 1 km wide. Each zone contains four parallel shorelines, which demarcate distinct progradational phases and indicate different stages of lake regression. These shorelines imply that the ancient lake was stable for extended periods and was not ephemeral in nature. The integration of the radar images with data from the Shuttle Radar Topography Mission (SRTM) shows that the segments have a constant altitude of ~573 m asl. The use of GIS techniques enabled the delineation of the lake borders and the extent of its endorheic drainage basin. This basin occupies a total surface area of ~ 128 802 km2 and comprises nine main tributaries. The largest of these tributaries occupies an area exceeding 21 672 km2, with a main channel length of approximately 435 km. The basin is centered by the large terminal paleolake that occupied an area of ~30 750 km2 with about 2530 km3 of water when complete filled.

Much of the lake's water would have seeped through the sandstone substrate to accumulate as groundwater. This paleolake will have significant consequences for enriching our knowledge of continental climate change and regional palaeohydrology and should be taken into consideration in learning of past human habitation in the region. The presence of this mega lake, in the Sudanese province of Darfur, might supply groundwater for a region stricken by both the drought and the resulting war. Field visit to the site will be conducted in the summer of 2007 for ground verification and soil sample analysis in order to determine the age of the paleolake.