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Weathering and Soil

Weathering is the breakdown and state alteration of rocks at or near the surface of the earth through a set of physical, chemical and biological processes. Both rocks and soil undergo changes either physically, through disintegration, or chemically, through decomposition. This processes frequently involves water as an agent as it is the direct cause of frost shattering, wetting and drying, and other processes. Weathering is actually directly affected by climatic factors, hence it acquired its name.

Most of the weathering activities occur at the earth’s surface as both weather and climate as the driving forces are located here, therefore weathering decreases with depth (Strahler and Strahler 320). Erosion on the other hand is the process of particle displacement, which is applicable to rocks and soil, as they are carried by different agents such as water, wind, ice, and even organisms. This is the removal of particles form one location to another on the earth’s surface.

The difference of erosion from weathering is that the former involves motion or movement, apart from weathering that only involves breakdown with the particles simply remaining in stasis (Abou-Shalah et al. 3). Transportation itself is the mode which erosion displaces particles form their place of origin. Weathering and erosion more often than not occur simultaneously and hand in hand. Rocks are mostly form underneath the earth’s surface and they become exposed when natural phenomena occur such as volcanism and mountain formation.

Upon exposure to the earth’s surface, with climate and weather playing as major factors, rocks consequently breakdown into sediments through the mentioned process of weathering. When these rocks are weathered into smaller particles, they are transported through different agents that cause the sediments to become even more abraded and worn down. As the distance they have traveled increases, they become more smaller and more rounded and eventually settle and become part of the soil composition of the area (Grotzinger et al. 329). Author’s Name 2

Mechanical and Chemical Weathering There are two recognizable types of weathering, namely mechanical or physical and chemical weathering. The major difference between these two types is that in mechanical weathering, only the shape and size of the solid particles are changed while in chemical weathering the composition of the rocks and sediments are altered. Mechanical weathering involves the gradual physical breakdown of bigger rocks, dividing it further into smaller pieces. Here, the mineral contained in the original rock is identical to its subsequent fragments.

Chemical weathering involves mineral composition change, in which these mineral are either modified or destroyed. Due to the chemical reactions transpiring when new particles are formed and due to dissolution of particles in water, the rocks are changed chemically (Abou-Shalah et al. 3). Generally, these two processes result to different type of rocks. Mechanical weathering mostly produces cladistic rocks and sedimentary rocks such sand and sandstone. It also causes the formation of grains of quartz from a granite. Chemical weathering on the other hand brings about biological and chemical sediments such as limestone and rock salt .

Clay formation can also be attributed to chemical weathering, as it is a result of chemical reactions of mineral particles. Both physical and chemical weathering involve different kinds of processes. The process in which rocks become frozen and become brittle enough to fracture into pieces is called frost shattering. The rock expands as water is forced into the rock and gives pressure into it. Another process is called hydration where soil aggregates disintegrate due to wetting and drying that cause expansion and contraction.

Another example of physical weathering is insolation or thermal weathering, where differential temperature between day and night causes stress on rocks and causes them to again contract and expand. Chemical weathering on the other hand involves processes such as carbonation, hydrolysis, chelation, and oxidation. Carbonation is the dissolution of calcium carbonate ions in acidic groundwater while hydrolysis is the replacement of mineral cations by hydrogen ions from acidic water. When mineral cations and organic molecules bond, this results to Author’s Name 3

chleation, which frequently occurs due to plants. Oxidation is the loss of an electron to dissolved oxygen (Strahler and Strahler 321). Effect of Climate on Soil Formation Climate is one of the most widely accepted cause of the regulation of erosion rates. Different places with different climatic conditions considerably differ in their types of soil and their soil profile. Seasonal trends cause variations in soil, as more rains can cause higher rates of soil erosion and therefore more soil formation. Drying seasons have lower levels of water, decreasing the agent of particle movement.

Other factors involve nitrogen and organic-matter content of suface soils. These increase with higher moisture levels, as exemplified by grassland soils. Nitrogen levels also affect decomposition rates, as these are typically low in regions such as the arid areas of the world. This is due to the very rapid decomposition by plant species as stimulated by neutral soil reaction. Places with higher precipitation causes higher levels of rainwater causing soil materials to be removed form their location. There is more movement than in arid areas where weathering occurs without much particle displacement (Hans 78-104).Author’s Name

Works Cited

Abou-Shalah, H. , E. Frith, L. MacDonald, C. Tait, J. Waldron, and S. Woods. “The Earth: Atlantic Canada Perspective. ” 1998. Saint Mary’s University. December 4, 2007 <http://www. stmarys. ca/conted/webcourses/GEO/GEO99/pubweather/intro. html>. Grotzinger, John, Frank Press, Raymond Siever, and Thomas H. Jordan. Understanding Earth. New York: W H Freeman & Co. , 2006. Hans, Jenny. Factors of Soil Formation. New York: Dover Publications Inc. , 1994. Strahler, A. H. And A. N. Strahler. Introducing Physical Geography. New York: Wiley and Sons, 2005

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