HPU NCS220 Weathering and erosion

• 1. Chapter 10 Weathering, Soil and Erosion Earth Science and the Environment (4th ed) Thompson & Turk

2. 10.1 Weathering and erosion Weathering processes that decompose rocks into sediments Mechanical (physical) weathering physical disintegration without chemical change Chemical weathering reaction with air/water creates a product different physically and chemically 3. 10.2 Mechanical weathering Pressure release fracturing formerly buried rocks expand when uncovered Frost wedging water in cracks expands when frozen Abrasion rock particles moving in contact wear each other away 4. Weathering Cont Organic activity roots Thermal expansion / contraction Organic Action Thermal Expansion 5. 10.3 Chemical weathering Dissolution many minerals dissolve to some degree Hydrolysis reaction with water, new mineral forms Oxidation reaction with oxygen, new mineral forms 6. Destructional -Weathering Landscapes broken down by chemical & physical processes & erosion Physical includes temperature changes (freezing and thawing, thermal expansion), crystal growth, pressure, plant roots, burrowing animals causes disintegration of parent material and facilitates chemical weathering Chemical always in water includes hydration, hydrolysis, oxidation, reduction, carbonation and exchange examples : oxidation of Fe to form limonite, deposited in joints, inhibits groundwater flow hydrolysis of feldspars to form clay (kaolin) - forms infill for joints 7. Factors affecting the RATE of weathering 8. Factors affecting the RATE of Weathering Surface area Increases the areas exposed to water, chemicals and wind. Time The longer a rock is exposed the more weathering will occur Composition Some minerals are more susceptible to chemical reaction Climate Chemical reactions are sped up with high temperatures and moisture 9. Erosion Erosion is the MOVEMENT of the particles once they have been weathered. Erosion is caused by both wind and water. 10. Creation of Rock vs Soil Sedimentary Rock formation follows weathering and erosion when the particles undergo compaction and cementation this usually occurs at the bottom of lakes and oceans but can occur anywhere layers of sediment accumulate and are not disturbed. Soil formation occurs when weathered and eroded rock material mixes with humus or organic material and accumulates.