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General Geology: Weathering and Soil

General Geology: Weathering and Soil. Instructor: Prof. Dr. Boris Natalin. Principle processes. Weathering – disintegration and decomposition of rocks at or near the Earth’s surface Mass wasting – the transfer of rock fragments downslope under influence of gravity

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General Geology: Weathering and Soil

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  1. General Geology: Weathering and Soil Instructor: Prof. Dr. Boris Natalin

  2. Principle processes • Weathering – disintegration and decomposition of rocks at or near the Earth’s surface • Mass wasting – the transfer of rock fragments downslope under influence of gravity • Erosion – the incorporation and transportation of material by mobile agents as water, wind, or ice

  3. Types of weathering: - Mechanical weathering - Chemical weathering

  4. Fragmentation of rocks • Frost wedging • Expansion resulting from unloading • Thermal expansion • Organic activity

  5. Unloading

  6. Frost wedging Water expands about 9% upon freezing Ice Broken fragments fall to the base of the cliff and create talus Talus

  7. Joints

  8. Thermal expansion Rounded pebble disintegrated due to the rapid cooling

  9. Organic activity Weathering is accomplished by: • Plants • Burrowing animals • Human beings

  10. Chemical weathering Water is a good solvent

  11. Dissolution

  12. Acid increases the corrosive force of water • Transformation of solid into soluble • H+ is active ion • Formation of carbonic acid: • Water is a weak acid

  13. Dissolution of stone monuments

  14. Acid precipitation

  15. Oxidation • 4Fe + 3O2 → 2Fe2O3 • Hematite (Fe2O3) and limonite [Fe2O3(OH)] • Mine acid Hydrolysis

  16. Decomposition of potassium feldspar

  17. Products of granite weathering 1)

  18. Alteration caused by chemical weathering • Physical change of outcrops - Sharp corners are attacked more readily - Spheroidal weathering

  19. Spheroidal weathering

  20. Spheroidal weathering

  21. Rates of weathering • Rock characteristics • Climate • Topography

  22. Rock characteristics

  23. Rock characteristics granite marble

  24. Climate 3500 years in Egypt 75 years in New York

  25. Topography • Humid regions • Arid regions • Differential weathering

  26. Soil • Regolith – • Soil – • Humus –

  27. Composition of soil

  28. Soil formation • Parent material • Time • Climate • Plants and animals • Slope

  29. Parent material

  30. Residual and transported soil

  31. Time in soil formation • Short time – parent material • Long time – other factors, especially climate

  32. Climate in soil formation • Wet and hot climate • Dry climate • Precipitation leach various material from soil

  33. Plants and animals • Main function is to furnish organic matter to the soil • Soil fertility depends on amount of organic matter • Organic decay creates organic acids • Microorganisms and humus • Earthworms mix the soil

  34. Slope in soil formation • Steep slope • Bottomlands and valleys • Flat-to-undulating upland surfaces • Slope orientation

  35. Soil profile A soil profile is a vertical cross-section from the surface down to the parent rocks

  36. Soil profile humus Topsoil 30% humus True soil (solum) subsoil Time span of soil formation Layer A needs many hundreds to several hundreds years Layer B needs 10,000 to 100,000 years

  37. Soil type

  38. Soil type

  39. Laterite

  40. Soil erosion • It is a natural process • Human being can increase the fertility of soil • Human being can damage or destroy soil

  41. Soil erosion • Sheet erosion • Rills • Gullies

  42. Soil erosion • 9 billion metric tons per year • 24 billion metric tons per year • Wind erosion • Filling water reservoirs with sediments • Filling water reservoirs with pesticides and nutrients

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