Weathering is the process by which atmospheric factors contribute to the decomposition of rocks, minerals and soil. Unlike erosion, it does not involve the movement of matter by water, ice, gravity or wind. Rather, mechanical or physical forces either break down rocks without any deference to their chemical make-up or because a chemical force creates a change in some or all of the rock's mineral composition, according to Clive Glifford, author of the book "Weathering and Erosion."
Frost disintegration happens in climates where the temperature lingers around the freezing point. Water collects in porous rocks during the day, or when the temperature is above freezing, and then freezes as the temperature drops. Because water increases in volume by approximately 9 per cent as the temperature declines, internal pressure can trigger rocks to split open and crack by what is known as the "freeze-thaw action," according to the U.S. Department of Transportation.
Mechanical-biological weathering occurs when a living organism contributes to the natural breakdown of rock in a non-chemical way. For instance, when plants or trees grow on or by a rock, their roots travel inside the rock’s creases, pores and holes and crack open the rock as they expand and exert pressure by a process called "root wedging," according to the University of Wisconsin at Stevens Point. Animals burrowing in the ground or earthworms moving through the soil can also cause this type of weathering.
Unlike frost disintegration and mechanical-biological weathering, dissolution is a process in which chemical changes are necessary for weathering to occur. This happens when an acid comes in contact with a rock and creates a chemical reaction that can weaken and eventually dissolve the rock. For instance, when sulphur dioxide from active volcanoes or fossil fuels mixes with precipitation, sulphuric acid forms, creating acid rain which can erode rocks on contact, according to the U.S. Department of Transportation.
Like dissolution, chemical-biological weathering damages rocks and minerals via changes due to acidic solutions. To be considered biological weathering, however, acids have to originate from a living organism. For instance, according to the U.S. Department of Transportation, many types of moss and plants release chelating compounds (digestive acids) to free iron and aluminium minerals from rocks for absorption. Moreover, plant and animal respiration can introduce carbon dioxide into the soil which, when mixed with water, becomes an acid, further eating away at the rock.
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