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Weathering Types

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Weathering is the combination of processes that breaking down of rocks, soil and minerals, eventually transforming into sediment. On the other hand, disintegration or alteration of the rock surface in its natural or original position through physical, chemical and biological processes induced or modified by wind, water and climate.

Spheroidal Weathering
Spheroidal Weathering (Spheroidal weathering is most common among coarse-grained igneous rocks, especially granite and similar rock types. It is more likely to be found in warm climates, where mechanical weathering by freezing ice is less likely.) Source: https://sciencing.com/definition-spheroidal-weathering-23142.html

Weathering involves physical, chemical, and biological processes that act separately or more often together to cause fragmentation and decay of rock material. Physical decomposition causes mechanical disintegration of the rock and therefore depends on the application of force. Weathering involves breaking up the rock into the forming minerals or particles without disturbing the forming minerals. The main sources of physical Weathering are the expansion and contraction of heat, the erosion of overlapping materials, the release of pressure on the rock, alternatively the freezing and thawing of water, the dissolution of water between the cracks and cracks in the rock, the growth of plants and organisms in the rock. Organisms in the rock. Rock exchange usually involves chemical deterioration in which the mineral composition in the rock is altered, rearranged or redistributed. Rock minerals are subjected to solution, carbonation, hydration and oxidation with circulating water. These effects on the Weathering of minerals are added to the effects of living organisms and plants as nutrient extraction to rocks.

After the rock breaks, the remaining materials cause soil with organic materials. The mineral content of the soil is determined by the parent material; therefore, a soil derived from a single rock type may often be lacking in one or more minerals required for good fertility, whereas a ventilated soil from a mixture of rock types (such as glacial, aeolian or alluvial deposits) generally makes more fertile soils. In addition, most of the Earth’s landforms and landscapes are the result of decomposition processes associated with erosion and re-accumulation.

Explain the disintegration or dissolution of rocks and minerals on the Earth’s surface. Water, ice, acids, salts, plants, animals and changes in temperature are all weather conditions.

After a rock is shredded, a process called erosion removes rock and mineral fragments. No rock on earth can resist erosion.

Weathering and erosion constantly changes the rocky landscape of the Earth. Wear abrades exposed surfaces over time. Exposure time generally contributes to how vulnerable a rock is to weather conditions. Rocks buried under other rocks, such as lava, are less susceptible to wear and erosion than rocks exposed to wind and water.

It is the first step in soil production in weather conditions as it smooths hard, sharp rock surfaces. Small pieces of worn minerals mix with plants, animal remains, fungi, bacteria and other organisms. A single type of weathered rock generally produces infertile soil, the weathered materials from the rock collection are richer in mineral diversity and contribute to more fertile soil. Soil types associated with the weathered rock mixture include untouched and alluvial deposits until icing.

Picture from Stephen Marshak (Essentials of Geology)

Physical weathering or Mechanical weathering

Physical weathering, also called mechanical weathering or disaggregation, is a class of processes that cause rocks to break up without chemical change. The primary process in physical weathering is abrasion (the process by which clips and other particles are reduced in size).  Temperature, pressure, freezing and so on. Physical weathering may occur for reasons. For example, cracks resulting from physical weathering will increase the surface area exposed to the chemical effect, thereby increasing the rate of disintegration.

Frost wedging: Freezing water blows pipes and breaks bottles; because water expands when the walls of the container freeze and push. The same phenomenon occurs on the rock. When stuck water in a joint freezes, it forces the joint to open and may cause the joint to grow. These freezing wedges allow the blocks to be freed from solid bedrock.

Salt wedging: In arid climates, dissolved salt in groundwater precipitates and grows as crystals in open pore spaces in rocks. This process, called salt wedging, pushes apart the surrounding grains and weakens the rock so that when exposed to wind and rain, the rock disintegrates into separate grains. The same phenomenon happens along the coast, where salt spray percolates into rock and then dries.

Root wedging: Have you ever noticed how the roots of an old tree can break up a sidewalk? As roots grow, they apply pressure to their surroundings, and can push joints open in a process known as root wedging

Thermal expansion: When the heat of an intense forest fire bakes a rock, the outer layer of the rock expands. On cooling, the layer contracts. This change creates forces in the rock sufficient to make the outer part of the rock break off in sheet-like pieces. Recent research suggests that the intense heat of the Sun’s rays sweeping across dark rocks in a desert may cause the rocks to fracture into thin slices.

Animal attack: Animal life also contributes to physical weathering: burrowing creatures, from earthworms to gophers, push open cracks and move rock fragments. And in the past century, humans have become perhaps the most energetic agent of physical weathering on the planet. When we excavate quarries, foundations, mines, or roadbeds by digging and blasting, we shatter and displace rock that might otherwise have remained intact for millions of years more.

Chemical weathering

Chemical weathering changes the composition of rocks, often transforming them when water interacts with minerals to create various chemical reactions. Chemical weathering is a gradual and ongoing process as the mineralogy of the rock adjusts to the near surface environment. New or secondary minerals develop from the original minerals of the rock. In this the processes of oxidation and hydrolysis are most important. Chemical weathering is enhanced by such geological agents as the presence of water and oxygen, as well as by such biological agents as the acids produced by microbial and plant-root metabolism.

The process of mountain block uplift is important in exposing new rock strata to the atmosphere and moisture, enabling important chemical weathering to occur; significant release occurs of Ca2+ and other ions into surface waters.

Dissolution: Chemical weathering during which minerals dissolve into water is called dissolution. Dissolution primarily affects salts and carbonate minerals (Fig. B.6a, b), but even quartz dissolves slightly.

Hydrolysis: During hydrolysis, water chemically reacts with minerals and breaks them down (lysis means loosen in Greek) to form other minerals. For example, hydrolysis reactions in feldspar produce clay.

Oxidation: Oxidation reactions in rocks transform ironbearing minerals (such as biotite and pyrite) into a rustybrown mixture of various iron-oxide and iron-hydroxide minerals. In effect, iron-bearing rocks can “rust.”

Hydration: the absorption of water into the crystal structure of minerals, causes some minerals, such as certain types of clay, to expand. Such expansion weakens rock.

Organic or Biological Weathering

A number of plants and animals may create chemical weathering through release of acidic compounds, i.e. the effect of moss growing on roofs is classed as weathering. Mineral weathering can also be initiated or accelerated by soil microorganisms. Lichens on rocks are thought to increase chemical weathering rates.

Some plants and animals can cause chemical weathering through the release of acidic compounds, ie, classification of algae grown on the roof as degradation. Mineral weathering can also be initiated or accelerated by soil microorganisms. It is thought that lichens on the rocks increase the chemical weathering rates.

The most common forms of biological weathering are the release of chelating compounds (ie, organic acids, siderophores) and acidifying molecules (ie, protons, organic acids) to break down aluminum and iron-containing compounds in soils beneath plants. The decomposition of the remains of dead plants in the soil can form organic acids which, when dissolved in water, cause chemical weather conditions. Excessive release of chelating compounds can easily affect the surrounding rocks and soils and lead to soils podsolization.

Joints

Almost all rocks found at or near the surface are broken up by fractures called joints. Rocks buried deep beneath the surface are under great pressure, but when the rock is no longer deeply buried, this pressure releases and the rock can expand a little. Because rocks are brittle, they break instead of stretching. The resulting breaks or joints form a network of near-vertical cracks that cross at high angles.

Weathering of Man-Made Structures

The rock blocks used to build some of the oldest structures of mankind were exposed to global weather conditions after installation. Granite blocks used to build pyramids in Mexico and a Roman aqueduct in Spain show the effects of global weather conditions after 2,000 years of wind and rain.

Credits: Marshak, S., & Repcheck, J. (2009). Essentials of geology. WW Norton.

Cite this article as: Geology Science. (2019). Weathering Types. [online] Available at: http://geologyscience.com/general-geology/weathering-types/ [14th September 2019 ]
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