Weathering and erosion are two basic events that take place on earth as part of the wear and tear of the natural resources like rocks, soils, and plants and trees that cover the earth. Closely observing weathering and erosion will help understand how the surface of the planet has been changing over the past several years and how it will change in the future as well. Weathering is the process through which rocks on the surface of the earth gradually break down into small pieces. On the other hand, erosion is the process through which the broken pieces and sediments are transferred from one part of the earth to another through agents like wind, raindrops, runoff, glaciers and plant roots. Thus, weathering and erosion, through their combined action, play a major role in shaping the landscapes on the face of the earth.
Primarily, weathering is classified into two types; physical or mechanical as well as chemical weathering. Physical weathering is promoted by the change of temperature on the surface of the earth. For example, when water seeps into a rock through minor cracks and freeze down due to temperature change it slowly expands. As a result, nearby rock formations slowly split up. When the water melts due to rise in temperature, the water flows down washing away rock bits. Similarly, chemical weathering occurs when the very composition of the constituents of the earth like rocks and soils is changed due to the presence of certain external agents (Yatsu, 1988). For instance, presence of higher concentration of carbon dioxide gas in the atmosphere leads to production of carbonic acid on the gas getting mixed with rain water. Over a period of time carbonic acid breaks up rocks. More importantly, human beings and animals, both domestic and wild, speed up the process of weathering through trampling and other physical actions upon rocks and soils. Limited rainfall in desert landscapes makes the weathering process extremely slow. At the same time, breaking down of rocks happens relatively quickly in arid regions than wet regions as vegetal cover protects the land surface from getting weathered.
Apart from the action of rain water that flows as streamlets to transport weathered rocks and soils from one place to another, erosion is also promoted by glaciers or ice, gravity and wind. In other words, the sun that energizes glaciers to flow as runoff and air to blow as wind indirectly causes erosion. Soil erosion causes severe problems by taking away fertile top soils and leaving farm lands with unproductive soil. Similarly, when soil gets eroded plants and buildings supported by soil get destabilized and destroyed. Rivers shape the landscape in various ways as they move from their source to mouth. For instance, river banks get eroded by the velocity of the runoff as a result of which sections of the river bank fall into the river and divert the flow to change the shape of adjoining landscapes.
Riverside erosion occurs in four different forms. Water-flow in rivers acts in two ways to cause erosion; by gradually scouring the sides and promoting large scale destruction of the embankments. First and foremost, the force of the running flow causes air to enter the cracks and holes along both sides of the river. The pressure of air gradually weakens the banks and as a result soil on the sides cave in to block the flow and change the course of the flow (Christopherson, 2011). In other words, the pressure building up inside the embankments leads to mass failure of the sides. Secondly, abrasion facilitated by small rocks that flow along with the water wears the river bed and sides to cause soil erosion. Thirdly, soluble particles present in the side embankments get dissolved in the water when water comes into contact with them. For instance, acid present in the water dissolves rocks on the sides and bed of the flow. Fourthly, the process of attrition, in which rock pieces come into contact with each other to be broken into still smaller fragments before getting washed away, promotes riverside erosion.
References
Christopherson, R.W. (2011). Geosystems: An introduction to physical geography. New York: Pearson.
Yatsu, E. (1988). The Nature of Weathering: an introduction, Sozosha, Tokyo.
