Weathering .

WeatheringWeathering

http://amazingworld.5u.com/photo.htmlhttp://amazingworld.5u.com/photo.html

ObjectivesObjectives

• Define weathering

• Identify causes of weathering– Physical or Mechanical Weathering– Chemical Weathering– Biological Weathering

•Discuss soil formation

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

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.

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

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.

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

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

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

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

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

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

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

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

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

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.

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

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