Weathering refers to the disintegration of rocks into small particles. Weathering is important because it results into formation of soil.
PHYSICAL WEATHERING
The rocks are disintegrated and are broken down to comparatively smaller pieces, without producing any new substances Physical condition of rocks
•Mechanical weathering breaks down rocks because of environmental factors that include heat, cold, water and wind. One form of mechanical weathering is constant freezing of water.
•Freezing of water
•Water, in liquid form, penetrates joints and holes within a rock. It starts freezing as temperatures drop to 32 degrees fahrenheit and below. As the water freezes, it expands and becomes about 10 percent larger.
This expansion pushes the cracks and holes in rocks outward causing the rock to break Alternate wetting and Drying During dry summer/ dry weather – these clays shrink considerably forming deep cracks or wide cracks. On subsequent wetting, it swells. This alternate swelling and shrinking/ wetting or drying of clay enriched rocks make them loose and eventually breaks Action of glaciers Action of wind In cold regions, when snow falls, it accumulates and change into a ice sheet. These big glaciers start moving owing to the change in temperature and/or gradient.
On moving, these exert tremendous pressure over the rock on which they pass and carry the loose materials Wind has an erosive and transporting effect. Often when the wind is laden with fine material e.g , fine sand, silt or clay particles, it has a serious abrasive effect and the sand laden winds itch’ the rocks and ultimately breaks down under its force
CHEMICAL WEATHERING.
Decomposition of rocks and minerals by various chemical processes is called chemical weathering. It is the most important process for soil formation.
• Chemical weathering takes place mainly at the surface of rocks and minerals with disappearance of certain minerals and the formation of secondary products (new materials).
• Chemical weathering becomes more effective as the surface area of the rock increases.
• Since the chemical reactions occur largely on the surface of the rocks, therefore the smaller the fragments, the greater the surface area per unit volume available for reaction
Carbonation • Carbon dioxide when dissolved in water it forms carbonic acid. This carbonic acid attacks many rocks and minerals and brings them into solution. • The carbonated water has an etching effect up on some rocks, especially lime stone. The removal of cement that holds sand particles together leads to their disintegration
Oxidation • The process of addition and combination of oxygen to minerals. The absorption is usually from O dissolved in soil water and that present in atmosphere.
•The oxidation is more active the presence of moisture and results in hydrated oxides. (e.g) minerals containing Fe and
Hydration • Chemical combination of water molecules with a particular substance or mineral leading to a change in structure. Soil forming minerals in rocks do not contain any water and they under go hydration when exposed to humid conditions.
•Up on hydration there is swelling and increase in volume of minerals. The minerals loose their luster and become soft hence breaking down. Biological Weathering
•Unlike physical and chemical weathering, the biological or living agents are responsible for both decomposition and disintegration of rocks and minerals. The biological life is mainly controlled largely by the prevailing environment.
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