1. Weathering

2. Objectives Define weathering Identify causes of weathering
Physical or Mechanical Weathering
Chemical Weathering
Biological Weathering
Discuss soil formation

3. Weathering
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.

4. Effects 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.

5. Chemical Weathering
Involves the alteration of the chemical composition of weathered material.
There are different process that result in chemical weathering including:
Hydrolysis
Oxidation
Carbonation

6. Hydrolysis Chemical 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 surface
by forming new compounds, and by increasing the pH of the
solution through the release of the hydroxide ions.
- Silicate minerals weather by hydrolysis to form clay.

7. Oxidation Chemical attachment of free oxygen to other
elements 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.

8. Carbonation Dissolving of calcium carbonate (limestone) in
acidic 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.

9. Physical Weathering Frost Wedging Exfoliation or Unloading
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

10. Frost 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.

11. Exfoliation or Unloading
Expansion of rock caused by lifting and erosion
Rock breaks off into sheets along joints that parallel surface.

12. Thermal 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.

13. Plant 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.

14. Biological 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.
animals

15. Soil 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_ jpg

16. Five Soil Forming Factors
Parent Material- The primary material from which rock is formed.
Climate- Weathering forces including heat, rain, ice snow, wind, etc.
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.
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.
Time- The formation of soil takes years.

17. Topography
Image courtesy of the United States Department of Agriculture, Soil Conservation Service

18. References http://uregina.ca/~sauchyn/geog221/wthrng.html