Erosion

In physical geography, erosion is the displacement of solids (earth, mud[?], rock and so on) through natural causes. There are several causes of erosion, the most common being water or wind movements. As the material is removed, it is carried to other locations and deposited as silt. This deposition is called sedimentation[?], and most of the silt created by erosion ends up in sediment layers.

Erosion is in itself a naturally occurring process, but it is in many cases increased by human activities. Some of those include deforestation, overgrazing and trail-building[?], activities that may result in soil degradation. Likewise, humans have sought to limit erosion by terrace[?]-building and tree planting.

One of the most serious and long-running water erosion problems on the planet is in China, on the middle reaches of the Yellow River and the upper reaches of the Yangtze River. From the Yellow River, over 1.6 billion tons of sediment flow each year into the ocean. The sediment originates primarily from water erosion in the Loess Plateau region of northwest China. (World Bank 2001: China: Air, Land, and Water).