Earth Materials and Processes

1. Earth Materials and Processes • Understand Basic Concepts of: • tectonic cycle • hydrologic cycle • geochemical cycle • rock cycle (interaction with above three) • minerals (silicates, oxides, carbonates, etc.) • weathering -- chemical, physical • erosion, transport, deposition, lithification GEOL g406 Environmental Geology S. Hughes 2003

2. Tectonic Plates, Earthquakes, and Active Volcanoes GEOL g406 Environmental Geology S. Hughes 2003

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4. Earth Materials and Processes The Rock Cycle Tectonism controls the rock cycle and is important to many surficial processes and other Earth Cycles. GEOL g406 Environmental Geology S. Hughes 2003

5. Earth Materials and Processes The Hydrologic Cycle GEOL g406 Environmental Geology S. Hughes 2003

6. Earth Materials and Processes • The hydrologic cycle describes the movement of water between the mediums of atmosphere, earth, and ocean and back again. In the process, water erodes the land, transports elements as sediment or in solution, and provides essential water resources for humans. Only 0.3 % of the total water in the cycle available for human use. • QUESTIONS: • Fresh water makes up what proportion of total water on earth? • Approximately what percent of water worldwide is considered polluted? GEOL g406 Environmental Geology S. Hughes 2003

7. Earth Materials and Processes The Biogeochemical Cycle traces the movement of an element, like carbon, in the air, water, on and in the land, and as used by living organisms. This issue is of particular importance today because large amounts of carbon dioxide are produced by burning fossil fuels. Many scientists are concerned that this trapped carbon dioxide may heat the earth in a process known as the "greenhouse effect." QUESTIONS: • How much carbon dioxide enters the Earth’s atmosphere each day? • What is carbon dioxide’s residence time in the atmosphere? • Where does the carbon "go" when its residence time in the atmosphere is over? (hint: check out the carbon cycle) GEOL g406 Environmental Geology S. Hughes 2003

8. Strength of Rocks GEOL g406 Environmental Geology S. Hughes 2003

9. Earth Materials and Processes GEOL g406 Environmental Geology S. Hughes 2003

10. Strength of Rocks • Rock strength is highly variable. • Many Factors: • rock type • texture • chemical composition • internal structures • presence or absence of fluids • Most rocks already fractured by joints and faults. • Fractured rocks are only as strong as whatever is holding the rock together (gravity or friction). • fracture along planes of weakness • fracture along bedding planes or along foliation planes • orientation of planes of weakness is important, Why? GEOL g406 Environmental Geology S. Hughes 2003

11. Strength of Rocks Some common rocks, shales for example, may share the same name but have different engineering properties depending on their deposition as well as lithification processes. Compaction shales are weak and can slide along bedding planes, slake (soften into mud when wet), and swell under certain conditions. Cemented shales, depending on the cementing material, can be very strong and suitable for most engineering enterprises. Study the stress-strain diagrams carefully. Read Table 2.1 in the textbook. GEOL g406 Environmental Geology S. Hughes 2003

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15. Earth Materials and Processes • Terms to Understand: • hydrocompaction • geologic cycle • tectonic cycle • rock cycle • hydrologic cycle • biogeochemical cycle • greenhouse effect • rock strength • reliable strength • safety factor • stress and strain • ductile and brittle substances • elastic and plastic deformation • proportional elastic limit • ultimate strength • rupture strength Read Case Histories in the textbook: Baldwin Hills Dam and St. Francis Dam GEOL g406 Environmental Geology S. Hughes 2003