Term: Weathering

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**Physical Weathering:**
– Disintegration of rocks without chemical change
– Breakdown into smaller fragments through processes like expansion and contraction
– Types include freeze-thaw weathering and thermal fracturing
– Pressure release can also cause weathering
– Often occurs hand in hand with chemical weathering

**Chemical Weathering:**
– Chemical reactions with water, oxygen, and carbon dioxide change rock composition
– Water converts primary minerals to secondary minerals via hydrolysis
– Oxygen oxidizes many minerals
– Mountain block uplift exposes new rock strata to weathering
– Chemical weathering changes original minerals into a new set closer to surface conditions

**Biological Weathering:**
– Lichens and mosses create a humid microenvironment on rock surfaces
– Lichens pry mineral grains loose from shale with hyphae
– Seedlings and plant roots exert physical pressure on rocks
– Living organisms contribute to both mechanical and chemical weathering
– Enhance physical and chemical breakdown of rock surfaces

**Weathering Effects:**
– Buildings made of stone, brick, or concrete are susceptible to weathering
– Natural weathering processes damage statues and monuments
– Acid rain accelerates weathering of buildings
– Design strategies can moderate the impact of environmental effects on buildings
– Concrete mixes with reduced water content minimize the impact of freeze-thaw cycles

**Soil Weathering and Formation:**
– Granitic rock weathers to clay minerals and iron oxides
– Well-weathered soils are depleted in calcium, sodium, and ferrous iron
– Basaltic rock weathers more easily due to fine grain size and volcanic glass presence
– Basalt weathers to clay minerals and aluminium hydroxides in tropical settings
– Soil formation requires between 100 and 1,000 years, resulting in various paleosol beds

Weathering (Wikipedia)

Weathering is the deterioration of rocks, soils and minerals (as well as wood and artificial materials) through contact with water, atmospheric gases, sunlight, and biological organisms. Weathering occurs in situ (on-site, with little or no movement), and so is distinct from erosion, which involves the transport of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity.

A natural arch produced by erosion of differentially weathered rock in Jebel Kharaz (Jordan)

Weathering processes are divided into physical and chemical weathering. Physical weathering involves the breakdown of rocks and soils through the mechanical effects of heat, water, ice, or other agents. Chemical weathering involves the chemical reaction of water, atmospheric gases, and biologically produced chemicals with rocks and soils. Water is the principal agent behind both physical and chemical weathering, though atmospheric oxygen and carbon dioxide and the activities of biological organisms are also important. Chemical weathering by biological action is also known as biological weathering.

The materials left over after the rock breaks down combine with organic material to create soil. Many of Earth's landforms and landscapes are the result of weathering processes combined with erosion and re-deposition. Weathering is a crucial part of the rock cycle, and sedimentary rock, formed from the weathering products of older rock, covers 66% of the Earth's continents and much of its ocean floor.

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