Geology

Sediment Sources

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Science  01 Dec 2006:
Vol. 314, Issue 5804, pp. 1355
DOI: 10.1126/science.314.5804.1355c

The Nile River drains much of northeast Africa, and its sediments reflect erosion across the continent. Dams such as the Aswan have caused efficient collection of these sediments in the human-made lakes that form behind them. Garzanti et al. examined the mineralogy and amount of sand dumped by the Nile into these lakes and found that ∼200 million metric tons of sediment are transported per year, several times the quantities estimated previously. The sand is mainly composed of basaltic rock or feldspar and metamorphic minerals, indicative of the Ethiopian highlands, an area of abundant deforestation and farming that receives monsoon rainfall during summer. Thus, a relatively small area of the Nile drainage, greatly affected by humans, supplies most of the sediments carried by the river to artificial lakes. — BH

Earth Planet. Sci. Lett. 10.1016/j.epsl.2006.10.001 (2006).

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