Erosion and Weathering 11/22/2018 Chapter 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. 11/22/2018 Chapter 2

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. 11/22/2018 Chapter 2

1.2.1 – 1.2.2 Physical Weathering Physical Weathering Is the breakdown of rock and minerals by mechanical stress. There are many examples… 11/22/2018 Chapter 2

Weathering There are two types : physical and chemical. 11/22/2018 Chapter 2

1.2.1 – 1.2.2 Physical Weathering Frost Fracture / Wedging The expansion of freezing water that causes rocks to crack. 11/22/2018 Chapter 2

1.2.1 – 1.2.2 Physical Weathering Heat Expansion When heated, rocks can expand and subsequently fracture. 11/22/2018 Chapter 2

1.2.1 – 1.2.2 Physical Weathering Plant Growth / Root Wedging Expansion due to root growth. 11/22/2018 Chapter 2

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. 11/22/2018 Chapter 2

1.2.1 – 1.2.2 Physical Weathering Animal Activity Animals tunnel into soil introducing water, air, etc. 11/22/2018 Chapter 2

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 11/22/2018 Chapter 2

1.2.2 & 1.2.3 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 11/22/2018 Chapter 2

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. 11/22/2018 Chapter 2

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 11/22/2018 Chapter 2

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. 11/22/2018 Chapter 2

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. 11/22/2018 Chapter 2

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. 11/22/2018 Chapter 2