Weathering .
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Transcript of Weathering .
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WeatheringWeathering
http://amazingworld.5u.com/photo.htmlhttp://amazingworld.5u.com/photo.html
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ObjectivesObjectives
• Define weathering
• Identify causes of weathering– Physical or Mechanical Weathering– Chemical Weathering– Biological Weathering
•Discuss soil formation
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WeatheringWeathering
Weathering is a set of physical, chemical, and biological processes that alter the physical and chemical state of rocks and soil at or near the earth's surface. http://www.uh.edu/~jbutler/physical/chapter6.htmlhttp://www.uh.edu/~jbutler/physical/chapter6.html
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Effects of WeatheringEffects of Weathering
• Loss of atoms and molecules from weathered surfaces.
• Addition of specific atoms to the weathered surface.
• Breakdown of one mass into two or more masses.
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Chemical WeatheringChemical Weathering
• Involves the alteration of the chemical composition of weathered material.
There are different process that result in chemical weathering including:– Hydrolysis – Oxidation – Carbonation
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HydrolysisHydrolysisChemical weathering is a process that involves the reaction between mineral ions and the ions of water (OH- and H+), and results in the decomposition of the rock surfaceby forming new compounds, and by increasing the pH of thesolution through the release of the hydroxide ions.
- Silicate minerals weather by hydrolysis to form clay.
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OxidationOxidationChemical attachment of free oxygen to otherelements and compounds.
Iron-bearing silicate minerals that undergo oxidation include the following: – pyroxene – amphibole – biotite – olivine
Rocks that contain these elements weather by oxidation into an orange color.
http://wwwrses.anu.edu.au/research/annrep/ar2006/ee/index.php?p=pillanshttp://wwwrses.anu.edu.au/research/annrep/ar2006/ee/index.php?p=pillans
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CarbonationCarbonationDissolving of calciumcarbonate (limestone) inacidic groundwater
- similar to hydrolysis but all the products are ionic and there is no residue - produces bicarbonate (HCO3), a major part of the dissolved load of most rivers - the carbonation of limestone results in karst topography: caves, sinkholes, etc.
http://www.khaolaklanddiscovery.com/_images/tours/http://www.khaolaklanddiscovery.com/_images/tours/khao_sok/old_coral_big.jpgkhao_sok/old_coral_big.jpg
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Physical WeatheringPhysical Weathering• Breakdown of mineral or rock material by entirely
mechanical methods brought about a variety of reasons.
– Frost Wedging– Exfoliation or Unloading– Thermal Expansion– Plant Wedging
http://members.aol.com/rhaberlin/mwstyg.htmhttp://members.aol.com/rhaberlin/mwstyg.htm
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Frost WedgingFrost Wedging• Mechanical disintegration, splitting
or break up of rock by the pressure of water freezing in
cracks, crevices, pores, etc.
• Caused by repeated freeze-thaw cycle of water in extreme climates. http://regentsprep.org/Regents/earthsci/units/weathering/frostwedging.gifhttp://regentsprep.org/Regents/earthsci/units/weathering/frostwedging.gif
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Exfoliation or UnloadingExfoliation or Unloading
• Expansion of rock caused by lifting and erosion
• Rock breaks off into sheets along joints that parallel surface.
http://facstaff.gpc.edu/~pgore/Earth&Space/condestr.htmlhttp://facstaff.gpc.edu/~pgore/Earth&Space/condestr.html
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Thermal ExpansionThermal Expansion
• Repeated cooling and heating of rock.
• Heat caused rock to expand and cooling causes rock to contract
• Looks very similar to frost wedging and salt crystal growth, but typically occurs in climates of extreme weather changes.
Thermal shattering of sandstone by forest fire. http://w3.salemstate.edu/~lhanson/gls210/gls210_weath1.htm
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Plant WedgingPlant Wedging
• Plant roots can wedge into cracks in rocks and produce enough pressure to split them
• Chemicals produced by the roots of plants help in the chemical weathering, as enzymatic activity digest the rock as the plant searches for nutrients in the rock.
http://facstaff.gpc.edu/~pgore/Earth&Space/condestr.htmlhttp://facstaff.gpc.edu/~pgore/Earth&Space/condestr.html
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Biological WeatheringBiological Weathering• Animals and Plants can
assist in breaking down rocks into sediment and soil.
Biological Weathering can be
caused by:
• Roots of trees and other plants
• Lichens, fungi, and other microorganisms.
• animalshttp://w3.salemstate.edu/~lhanson/gls210/gls210_weath1.htm
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Soil FormationSoil Formation• Soil is formed from the
weathering of rocks and minerals.
• Surface rock breaks down by weathering and is mixed with organic material. Over time it creates a thin layer of soil.
lh3.google.com/.../s800/IMG_1466-1.jpg
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Five Soil Forming FactorsFive Soil Forming Factors
1. Parent Material- The primary material from which rock is formed.
2. Climate- Weathering forces including heat, rain, ice snow, wind, etc.
3. Organism- all animals living in or on the soil. Ex: Animals living in the soil will affect how soil is moved around and decomposition of waste materials.
4. Topography- the location of the soil on a landscape. Ex: Soil at the bottom of a hill will get more water than that on the slope.
5. Time- The formation of soil takes years.
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TopographyTopography
Image courtesy of the United States Department of Agriculture, Soil Image courtesy of the United States Department of Agriculture, Soil Conservation ServiceConservation Service
http://soil.gsfc.nasa.gov/soilform/parmat.htmhttp://soil.gsfc.nasa.gov/soilform/parmat.htm
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ReferencesReferences• http://uregina.ca/~sauchyn/geog221/wthrng.html• http://www.physicalgeography.net/fundamentals/10r.html• http://gpc.edu/~pgore/Earth&Space/condestr.html• http://geosun.sjsu.edu/paula/134/pdf/lecture3.pdf• http://library.thinkquest.org/J003195F/soil.htm• http://soil.gsfc.nasa.gov/soilform/parmat.htm• http://w3.salemstate.edu/~lhanson/gls210/gls210_weath1.htm