The Blue Nile
The headwaters of the Blue Nile are in the Ethiopian highlands at an elevation of 2500 meters. The plateau is built of basalt lava flows, and many volcanoes rise to heights over 4000 meters. The highlands are located perfectly to receive rain from the seasonal monsoons during the months of May or June through October. Over 2000 mm (2 m) of rain falls on the highlands during this short time. Many tributaries feed Lake Tana, which is the nominal headwater lake of the Blue Nile. The seasonal heavy rains cause the tributaries to erode deeply through the basaltic lavas during their steep descent from the plateau. The tributaries and the Blue Nile itself become deep brown in color as they carry clay and silt particles derived from the basalt. These suspended particles are rich in plant nutrients (calcium, magnesium, iron and to a lesser extent phosphorus) and form fertile soils when deposited. This fertilizer was used by the ancient Egyptians.
Important:The Blue Nile provides the fertile silt in the Nile Delta!!
