(e) Explain two disadvantages of weathering.
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Answer:
Many of the natural factors that affect the Earth's surface fall under one of the four elements. Air, fire, water and earth govern life on the planet. They tear down, reshape, destroy, recreate, modify and recycle the landscape continuously.
Whether subtle rain erosion or dramatic lava flows, they all contribute to changes in the landscape. With an erupting volcano, these changes may take only moments and the surrounding landscape is transformed into a new one. Rain falling on limestone boulders will slowly dissolve the minerals, reshaping the stone into sculptures over thousands, even millions, of years. Organisms such as animals and plants also affect the earth's surface through various means.
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Answer:
Weathering is the breaking down of rocks, soils, and minerals as well as wood and artificial materials through contact with the Earth's atmosphere, water, and biological organisms. Weathering occurs in situ (i.e., on site, without displacement), that is, in the same place, with little or no movement, and thus should not be confused with erosion, which involves the transport of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity and then being transported and deposited in other locations.
A natural arch produced by erosion of differentially weathered rock in Jebel Kharaz (Jordan).
Two important classifications of weathering processes exist – physical and chemical weathering; each sometimes involves a biological component. Mechanical or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure. The second classification, chemical weathering, involves the direct effect of atmospheric chemicals or biologically produced chemicals also known as biological weathering in the breakdown of rocks, soils and minerals.[1] While physical weathering is accentuated in very cold or very dry environments, chemical reactions are most intense where the climate is wet and hot. However, both types of weathering occur together, and each tends to accelerate the other. For example, physical abrasion (rubbing together) decreases the size of particles and therefore increases their surface area, making them more susceptible to chemical reactions. The various agents act in concert to convert primary minerals (feldspars and micas) to secondary minerals (clays and carbonates) and release plant nutrient elements in soluble forms.
The materials left over after the rock breaks down combined with organic material creates soil. The mineral content of the soil is determined by the parent material; thus, a soil derived from a single rock type can often be deficient in one or more minerals needed for good fertility, while a soil weathered from a mix of rock types (as in glacial, aeolian or alluvial sediments) often makes more fertile soil. In addition, many of Earth's landforms and landscapes are the result of weathering processes combined with erosion and re-deposition.