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Geology 12

Geology 12. Presents. Sedimentary Rocks. Weathering and Erosion. Weathering : the physical breakdown (disintegration) and chemical alteration (decomposition) of minerals and rocks at of near the Earth’s surface Erosion : removal of weathered material (by water, wind, or ice).

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Geology 12

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  1. Geology 12 Presents

  2. Sedimentary Rocks Weathering and Erosion

  3. Weathering: the physical breakdown (disintegration) and chemical alteration (decomposition) of minerals and rocks at of near the Earth’s surface • Erosion: removal of weathered material (by water, wind, or ice)

  4. 3 Types of Weathering: • 1. Physical/Mechanical Weathering: • Physical forces break rocks into smaller pieces without changing chemistry • 4 kinds • Frost action/ice wedging: water seeps into cracks, freezes, expands (9%) and pushes rock apart. Most effective in areas where temperature fluctuates above & below 0’C animation link

  5. Ice wedging cliff Joints = rock fractures Talus = debris accumulation

  6. 3 Types of Weathering • 1. Physical (Mechanical) Weathering: • a) Ice Frost Wedging

  7. Ice Frost Wedging

  8. Talus = fallen rock debris

  9. Talus cone

  10. Sheet joints • b) pressure release: many minerals/rocks are formed under immense pressure. When they are uplifted and exposed through erosion, the pressure is greatly reduced. The rock expands forming layer of fractures (joints)

  11. Exfoliation dome before after • Exfoliation: slabs of rock break along sheet joints and fall off • Popping/rock bursts: sudden pressure relief in deep mines rock explodes like a grenade injuring/killing miners

  12. B) Pressure Release

  13. Exfoliation Dome: Chief

  14. day night • c) Thermal expansion & contraction: rock is a poor heat conductor; in deserts where the temperatures rise and fall 30’C/day, the outside of the rock heats-expands and cools-contracts animation + dark minerals get hotter than white minerals

  15. C) Thermal Expansion and Contraction

  16. d) Salt crystal growth: salts in rock crevices grow. Expand prying the rock apart like ice wedging. • Road salt in roads & bridges, inside of concrete foundation.

  17. D) Salt Crystal Growth

  18. 2. Biological Weathering = activities of organisms • a) animals: burrow, tramp, bring materials to surface for more weathering, help transmit gases and water to depths, etc. Animation • b) plants: roots wedge rocks apart • Animation

  19. 2. Biological Weathering • A) Animals:Moles

  20. 2. Biological Weathering • A) Animals:ants

  21. 2. Biological Weathering • A) Animals:clams

  22. B:Plants:root wedging

  23. B:Plants: root wedging

  24. Lichens

  25. B) PlantsRoot Wedging

  26. B) PlantsRoot Wedging

  27. 3. Chemical Weathering: chemical alteration of rock/parent material • 3 kinds • a) Solution: a solid dissolves (halite, calcite) and is usually helped by CO2 in water which forms carbonic acid (also in plant roots) • Results in hard water, caves & karst topography (sink holes).

  28. 3. Chemical Weathering • A) Solution

  29. Sinkhole

  30. b) oxidation: reacts with oxygen to form oxides (rust). • Ferromagnesians (olivine, pyroxene amphibole & biotite) combine with O2 for form hematite or limonite. • Hi sulfur/sulfide coal acid rain/runoff • Iron sulfides (pyrite FeS2) sulphuric acid + iron oxide

  31. B) Oxidation

  32. Chevy: like a rock all right!

  33. c) Hydrolysis: cations (metals) in minerals are replaced by H+ from water • Ex: Potassium (K) Fs + water clay + K + silica • Ex: Plagioclase Fs + water clay + (Na, Ca) + silica

  34. C) Hydrolysis

  35. Kaolinite clay

  36. Terminology: • Differential Weathering: rocks that weather at different rates produce uneven surfaces Resistant cap rock Mesa/butte Hodo/ pinnacle rock plateau

  37. Differential Weathering Hard Caprock

  38. Spheroidal Weathering: reactangular rocks weather into roundish rocks because corners are attacked on 3 sides, edges on 2 sides, but flat planes on 1 side • Result: rounded (& smaller) rocks

  39. Spheroidal Weathering

  40. Resistance to Weathering poor good

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