1. Erosion and Weathering
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2. 1.2.1 Introduction: Weathering and Erosion
Weathering is the breakdown of rock and minerals.
Erosion is the removal of weathered sediment or rock by the forces of wind, water and ice.
Denudation. The process of exposing underlying rocks by weather AND erosion. Denudation is gradational. Gradational means the leveling of a land surface down to bedrock.
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3. Erosion
Erosion is the removal of weathered sediment or rock by the forces of wind, water and ice.
This is a two fold process:
1. Transportation which is the movement of sediment.
2. Deposition is the settling of sediments.
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4. 1.2.1 – 1.2.2 Physical Weathering Physical Weathering
Is the breakdown of rock and minerals by mechanical stress. There are many examples…
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5. Weathering There are two types : physical and chemical. 11/22/2018
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6. 1.2.1 – 1.2.2 Physical Weathering Frost Fracture / Wedging
The expansion of freezing water that causes rocks to crack.
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7. 1.2.1 – 1.2.2 Physical Weathering Heat Expansion
When heated, rocks can expand and subsequently fracture.
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8. 1.2.1 – 1.2.2 Physical Weathering Plant Growth / Root Wedging
Expansion due to root growth.
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9. 1.2.1 – 1.2.2 Physical Weathering Exfoliation
As pressure is released from certain rocks, it can cause layers to split and fall off.
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10. 1.2.1 – 1.2.2 Physical Weathering Animal Activity
Animals tunnel into soil introducing water, air, etc.
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11. 1.2.2 & *1.2.3 Chemical Weathering
This is the breakdown of rocks and minerals by chemical reactions and usually involves the action of rainwater.
Involves three processes:
The formation of Solutions
Hydrolysis
Oxidation
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12. 1.2.2 & Chemical Weathering
The formation of Solutions: Rainwater absorbs CO2 , SO2, and other chemicals from the atmosphere, along with organic acids from the soil. Produces acids
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13. Hydrolysis: Involves minerals in solution
Hydrolysis: Involves minerals in solution. The reaction of water with rocks and minerals causes some solids to dissolve and move away. Carbonic acid reacts with silicates. Produces a soft clay from which potassium, sodium and magnesium are subsequently leached.
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14. Oxidation is the reaction of metallic minerals to oxygen (mainly in water). This results in the formation of oxides, which tend to be softer than the original mineral. For example, rust on iron and green copper oxide on copper
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15. 1.2.4 Relate Environmental Conditions & Rate of: Chemical Weathering
Heavy rain, running water and/or an abundance of water, increases the amount of dissolving. Conversely less water leads to less dissolving.
High temperatures will increase the rate of chemical reactions. It is a chemistry fact that heat increases the speed of many reactions like oxidation.
Ocean water contains salt which can increase the rate of many reactions like oxidation.
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16. 1.2.4 Relate Environmental Conditions & Rate of: Physical Weathering
For regions with fast temperature changes (like the desert) there are increases in the amount of physical weathering due to heat expansion.
For regions where there is little temperature change (like the tropics), the amount of physical weathering due to heat expansion is minimal.
Abundant precipitation, combined with alternating freezing/thawing temperatures, increases the amount of frost fracture.
The absence of those climatic conditions (frost) reduces the amount of frost fracture.
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17. 1.2.4 Environment and Physical Weathering
Running water increases physical erosion as friction occurs between water and rock.
Ocean waves cause hydraulic pressure and abrasion on the shore leading to physical weathering.
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