Weathering
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Weathering. the process by which rocks on or near Earth’s surface break down and change. Two Types of Weathering. Mechanical (Physical) Weathering – only a physical change takes place. Chemical Weathering – a chemical change takes place. Mechanical Weathering.

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Weathering

Weathering

the process by which rocks on or near Earth’s surface break down and change


Two types of weathering
Two Types of Weathering

  • Mechanical (Physical) Weathering – only a physical change takes place.

  • Chemical Weathering – a chemical change takes place


Mechanical weathering
Mechanical Weathering

a physical change – the rock is simply broken down into smaller pieces


Examples of mechanical weathering
Examples of mechanical weathering

  • Freeze and Thaw Weathering

    When water freezes its volume increases and as result of which the crack gets larger. In the morning the frozen water thaws and gives space to more water, which follows the same procedure.


Examples of mechanical weathering1
Examples of mechanical weathering

Pressure

  • overlying rock layers are removed, the pressure on the bedrock below is reduced so that the surface rocks are able to expand

  • roots of trees and other plants grow an expand to exert pressure on the rocks to split


Chemical weathering
Chemical Weathering

Rocks and minerals undergo changes in their composition.

Atoms are rearranged into new compounds.

Agents of chemical weathering include water, oxygen, carbon dioxide, and acids.


Acid precipitation commonly called acid rain
Acid Precipitation (commonly called acid rain)

  • caused by the release of pollutants from burning of fossil fuels in industry and motor-vehicles.


Sandstone figure at a castle in germany built in 1702
Sandstone figure at a castle in Germany, built in 1702

Photograph taken in 1908 Photograph taken in 1968

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/AcidRain.html


Review question
Review question

What observations can you make that give you clues that a chemical reaction has occurred?

Change in color, change in temperature, bubbling or production of a gas


What affects the rate of weathering
What affects the rate of weathering?

  • climate

    • chemical weathering occurs readily in climates with warm temperatures, abundant rainfall, and lush vegetation

    • physical weathering occurs readily in cool, dry climates


What affects the rate of weathering cont d
What affects the rate of weathering? (cont’d)

  • Rock type and composition

    • in general, sedimentary rocks are more easily weathered than harder igneous and metamorphic rocks

  • Surface area

    • the greater the total surface area, the more weathering that occurs


What affects the rate of weathering cont d1
What affects the rate of weathering? (cont’d)

  • the amount of slope

    • materials on slopes have a greater tendency to move as a result of gravity, which exposes underlying rock surfaces which provides more opportunities for weathering to occur


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