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Although the terms erosion and denudation are used interchangeably, erosion is the transport of soil and rocks from one location to another, [1] and denudation is the sum of processes, including erosion, that result in the lowering of Earth's surface. [2]
Soil erosion is the denudation or wearing away of the upper layer of soil. It is a form of soil degradation . This natural process is caused by the dynamic activity of erosive agents, that is, water , ice (glaciers), snow , air (wind), plants , and animals (including humans ).
Superimposed drainage develops differently: initially, a drainage system develops on a surface composed of 'younger' rocks, but due to denudation activities this surface of younger rocks is removed and the river continues to flow over a seemingly new surface, but one in fact made up of rocks of old geological formation.
[1] [2] Removal of rock or soil as clastic sediment is referred to as physical or mechanical erosion; this contrasts with chemical erosion, where soil or rock material is removed from an area by dissolution. [3] Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres.
The amount of matter carried by a large river is enormous. It has been estimated that the Mississippi River annually carries 406 million tons of sediment to the sea, [5] the Yellow River 796 million tons, and the Po River in Italy 67 million tons. [6] The names of many rivers derive from the color that the transported matter gives the water.
The stream erodes away at the rock and soil at its headwaters in the opposite direction that it flows. Once a stream has begun to cut back, the erosion is sped up by the steep gradient the water is flowing down. As water erodes a path from its headwaters to its mouth at a standing body of water, it tries to cut an ever-shallower path.
Attrition is the process of erosion that occurs during rock collision and transportation. The transportation of sediment chips and smooths the surfaces of bedrock; this can be through water or wind. [1] Rocks undergoing attrition erosion are often found on or near the bed of a stream. [2]
Tectonic uplift results in denudation (processes that wear away the earth's surface) by raising buried rocks closer to the surface. This process can redistribute large loads from an elevated region to a topographically lower area as well – thus promoting an isostatic response in the region of denudation (which can cause local bedrock uplift).