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WEATHERING

WEATHERING . GEOLOGY NOTES Chapter 5. WEATHERING. Breakdown of rock due to weather no visible motion. MECHANICAL (PHYSICAL) WEATHERING. Disintegration Breaks into small pieces NO visible motion. MECHANICAL WEATHERING. Ice (frost wedging) water expands when freezes angular pieces.

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WEATHERING

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  1. WEATHERING GEOLOGY NOTES Chapter 5

  2. WEATHERING • Breakdown of rock due to weather • no visible motion

  3. MECHANICAL (PHYSICAL) WEATHERING • Disintegration • Breaks into small pieces • NO visible motion

  4. MECHANICAL WEATHERING • Ice (frost wedging) • water expands when freezes • angular pieces

  5. MECHANICAL WEATHERING • Sheeting(exfoliation) • pressure is removed from above • Fractures “peel” off

  6. Half-dome

  7. MECHANICAL WEATHERING • Other types • burrowing animals • Plant roots • Mud cracks

  8. When water evaporates- mud shrinks Mudcracks

  9. CHEMICAL WEATHERING • Decomposition • chemical change takes place

  10. CHEMICAL WEATHERING • Hydrolysis • reacts with acid/water to form clays • feldspar + carbonic acid + water clay + soluble minerals • common in granite

  11. CHEMICAL WEATHERING • DISSOLUTION ANY CARBONATE + CARBONIC ACID CALCIUM CARBONATE (soluble) • common in limestone • creates caves and sinkholes

  12. Parthenon, Greece

  13. sinkholes

  14. Sinkhole formation

  15. Areas prone to sinkholes

  16. Dissolution • Marble statue

  17. CHEMICAL WEATHERING • OXIDATION • reacts with O2 • Groundwater with Fe is powerful agent • minerals with high Fe content • hematite, limonite, olivine • intense in tropical climates

  18. Oxidation of basalt

  19. Pictured Rocks, MI

  20. PLANES OF WEAKNESS • WHERE ROCKS WILL BREAK • Joints- vertical fractures • bedding planes- horizontal fractures • Granular disintegration- cement in clastic rocks breaks down

  21. joints

  22. BEDDING PLANES

  23. Granular disintegration

  24. ROCK TYPES • Granite - exfoliation, hydrolysis (k-spar to clay) • quartz doesn’t weather • Basalt- chemical (oxidation) • Sandstone- granular disintegration • limestone- dissolution • shale- breaks down into clay

  25. Sandstone tombstone

  26. Granite

  27. Which rocks weather most rapidly? • sedimentary

  28. Which rocks are most resistant to weathering? • Igneous / metamorphic (exception?) • Bowen’s reaction series • Olivine most

  29. Differential weathering • Different rock types weather differently • OR • Different rates of weathering due to exposure

  30. Stairway to heaven, CO

  31. Bryce Canyon, UT

  32. arches

  33. Differential erosion limestone shale

  34. Hoo-doos

  35. CLIMATE AND WEATHERING • Chemical- warm and moist • Physical- freeze/thaw cycle

  36. CLIMATE • TROPICAL • Strong chemical • DESERT • Slight mechanical • POLAR • Slight mechanical • MID LATITUDE (MI) • Strong chemical and mechanical

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