Silt is easily transported in water and is fine enough to be carried long distances by air as 'dust'. Thick deposits of silty material resulting from aeolian deposition are often called loess (a German term) or limon (French). Silt and clay contribute to turbidity in water. Silt is transported by streams or by water currents in the ocean.
Silt, deposited by annual floods along the Nile River, created the rich and fertile soil that sustained the ancient Egyptian civilization. Silt deposited by the Mississippi River throughout the 20th century has decreased due to a system of levees, contributing to the disappearance of protective wetlands and barrier islands in the delta region surrounding New Orleans.
The main source of silt in urban rivers is disturbance of soil by construction activity . The main cause of river siltation in rural areas is erosion from plowing of farm fields, clearcut logging or slash and burn treatment of forests . When the total ground surface is stripped of vegetation the upper soil is vulnerable to wind and water erosion. Entire regions of countries have been rendered unproductive by erosion. On the Madagascar high central plateau, approximately ten percent of the country's land area, virtually the entire landscape is sterile, with gully erosive furrows in excess of 50 meters deep and one kilometer wide . Shifting cultivation is a farming system which incorporates the slash and burn method in some regions of the world. The resulting sediment load can cause extensive fish kills, hampering economic development .
Science whiz kids test their knowledge ; Teams from Bangor and Limestone compete with regional high schools in the Science Bowl at USM.
Feb 13, 2005; SETH HARKNESS Staff Writer Portland Press Herald (Maine) 02-13-2005 Science whiz kids test their knowledge ; Teams from Bangor...