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

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Weathering

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

  2. Two Types of Weathering • Mechanical (Physical) Weathering – only a physical change takes place. • Chemical Weathering – a chemical change takes place

  3. Mechanical Weathering a physical change – the rock is simply broken down into smaller pieces

  4. 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.

  5. 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

  6. 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.

  7. Acid Precipitation (commonly called acid rain) • caused by the release of pollutants from burning of fossil fuels in industry and motor-vehicles.

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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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