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Mini Dragon Group (ages 6-7)

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Ruben Lavrentiev
Ruben Lavrentiev

Sahara Sands

Beneath the sands of the Sahara Desert scientists have discovered evidence of a prehistoric megalake. Formed some 250,000 years ago when the Nile River pushed through a low channel near Wadi Tushka, it flooded the eastern Sahara, creating a lake that at its highest level covered more than 42,000 square miles.

sahara sands

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Wind can move between 60 and 200 million tonnes of fine dust up from the Sahara each year. Convection currents, which also cause other meteorological conditions like thunderstorms, can transport the dust over thousands of kilometres.

The Nile drainage basin, littoral cell and turbiditic cone represent the longest route of sediment transport on Earth. Complex interactions between "craton interior" and "volcanic rifted-margin" to "rift-shoulder" provenances take place along the Nile system, and can be quantitatively assessed by high-resolution bulk-petrography and dense-mineral analysis. The Ethiopian volcanic plateaux and basement uplifts, subject to intense seasonal rainfall and drained by the Abai (Blue Nile) and Atbara rivers, are the major source of rift-derived detritus. This latter mixes with sediments from the African craton carried by the White Nile and, further downstream, by Saharan winds. After nearly 6700 km of northward fluvial transport along the outer flanks of the East African and Northern Red Sea rift shoulders, sediments reaching the Mediterranean Sea were either funnelled downslope as turbidity currents or shifted eastward by longshore currents for another 600 km along the Sinai-Levant passive-margin as far as Northern Israel. During the Quaternary, the Nile system has undergone repeated changes related to climatic and eustatic fluctuations, and recently also to human activities. After construction of the Aswan High Dam in 1964, the delta has been cut off from sediment supply, and actually transferred inland to Lake Nasser. Nevertheless, due to incision of channel and bank deposits, original quartzofeldspathic composition of Nile sediments is progressively restored north of the dam. Detrital signatures indicate increasing contamination by eolian dust after dam construction, but still negligible supply from the undissected outer flank of the Gulf-of-Suez shoulder. Today, the starved delta is attacked by waves from the N-NW (the direction of greatest Mediterranean fetch), which drive massive eastward longshore drift. Mixing with quartzose Saharan sands occurs locally on the delta and becomes prominent along the dune-bordered coast of Northern Sinai. Wadi El Arish, draining the undissected outer flank of the Sinai shoulder, carries carbonaticlastic sands as far as 60 km from the coast, where it is choked by quartzose eolian sands. Similar abrupt variations from carbonaticlastic to quartzose compositions affect all Palestinian streams draining the outer flank of the Dead Sea shoulder, which extensively recycle Pleistocene eolianites ("kurkar ridges") across the coastal plain. Detritus from the rift shoulder becomes significant locally at the foot of Mt.Carmel, but Palestine beach sands as far as Akko are quartzofeldspathic, indicating ultimate origin mainly from the Nile delta.

Relations between the Arab nations of North Africa shift like the Sahara's sands, and past major-power agreements with those nations have had the instability of houses built on sand. Algeria, whose 700-mile girth splits the new union, is at odds with Morocco over the Western Sahara matter and would like King Hassan to negotiate with the Polisario.

A study was conducted to determine root development in a stratified and mixed sandy soil in the Sahara sands of Libya. Lucerne (Medicaqo sativa L.), millet (Pennisetum typhoides Burn.)> wheat (Triticum activumL.), grain sorghum (Sorghum bicolor L.), and several other crops were grown on soil that varied in depth to the stratified layers. Root depth and growth were measured by excavating along a representative root at intervals until the crop was mature or until no further root penetration into the subsoil occurred. 041b061a72


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