Es 14e lecture_ch04
- 1. © 2015 Pearson Education Ltd. Weathering, Soil, and Mass Wasting Chapter 4 Lecture Jennifer Mangan James Madison University Earth Science Fourteenth Edition, Global Edition
- 2. © 2015 Pearson Education Ltd. • Weathering – the disintegration and decomposition of material at or near the surface • Mass wasting – the transfer of rock material downslope under the influence of gravity • Erosion – the incorporation and transportation of material by a mobile agent, usually water, wind, or ice Earth’s External Processes
- 3. © 2015 Pearson Education Ltd. • Two kinds of weathering – Mechanical weathering • Breaking of rocks into smaller pieces – Chemical weathering • Chemical transformation of rock into one or more new compounds Weathering
- 4. © 2015 Pearson Education Ltd. Increase in Surface Area by Mechanical Weathering
- 5. © 2015 Pearson Education Ltd. • Four important processes – Frost wedging – expansion of freezing water – Salt crystal growth – Sheeting – generates onion-like layers and exfoliation domes – Biological activity Mechanical Weathering
- 6. © 2015 Pearson Education Ltd. Frost Wedging
- 7. © 2015 Pearson Education Ltd. Sheeting and Exfoliation of Igneous Rocks
- 8. © 2015 Pearson Education Ltd. • Alters the internal structures of minerals by removing or adding elements • Most important agent is water – Oxygen dissolved in water oxidizes materials – Carbon dioxide (CO2) dissolved in water forms carbonic acid and alters the material Chemical Weathering
- 9. © 2015 Pearson Education Ltd. • Weathering of granite – Weathering of potassium feldspar produces clay minerals, soluble salt (potassium bicarbonate), and silica in solution – Quartz remains substantially unaltered – Weathering of silicate minerals produces insoluble iron oxides and clay minerals Chemical Weathering
- 10. © 2015 Pearson Education Ltd. Chemical Weathering • Spheroidal Weathering – Generates rounded rocks – Weathering works inward from exposed surfaces
- 11. © 2015 Pearson Education Ltd. • Advanced mechanical weathering aids chemical weathering by increasing the surface area • Important factors – Rock characteristics • Mineral composition and solubility • Physical features such as joints Rates of Weathering
- 12. © 2015 Pearson Education Ltd. Rock Type Influences Weathering
- 13. © 2015 Pearson Education Ltd. • Important factors – Climate • Temperature and moisture are the most crucial factors • Chemical weathering is most effective in areas of warm temperatures and abundant moisture Rates of Weathering
- 14. © 2015 Pearson Education Ltd. • Differential weathering – Caused by variations in composition – Creates unusual and spectacular rock formations and landforms Rates of Weathering
- 15. © 2015 Pearson Education Ltd. Differential Weathering
- 16. © 2015 Pearson Education Ltd. • An interface in the Earth system • Soil is a combination of mineral matter, water, and air – Regolith • Rock and mineral fragments • Supports the growth of plants Soil
- 17. © 2015 Pearson Education Ltd. Soil Components
- 18. © 2015 Pearson Education Ltd. • Soil texture and structure – Texture refers to the proportions of different particle sizes • Sand (large size) • Silt • Clay (small size) – Loam (a mixture of all three sizes) is best suited for plant life Soil
- 19. © 2015 Pearson Education Ltd. Soil Texture
- 20. © 2015 Pearson Education Ltd. • Soil texture and structure – Structure • Soil particles clump together to give a soil its structure • Four basic soil structures – Platy – Prismatic – Blocky – Spheroidal Soil
- 21. © 2015 Pearson Education Ltd. • Parent material – Residual soil – parent material is the bedrock – Transported soil – parent material has been carried from elsewhere and deposited • Time – Important in all geologic processes – Amount of time to evolve varies for different soils Controls of Soil Formation
- 22. © 2015 Pearson Education Ltd. • Climate • Plants and animals – Organisms influence the soil’s physical and chemical properties – Furnish organic matter to soil Controls of Soil Formation
- 23. © 2015 Pearson Education Ltd. • Slope – Angle • Steep slopes often have poorly developed soils • Optimum is a flat-to-undulating upland surface – Orientation (direction the slope is facing) influences • Soil temperature • Moisture Controls of Soil Formation
- 24. © 2015 Pearson Education Ltd. Slopes and Soil Development
- 25. © 2015 Pearson Education Ltd. • Soil Profile – Soil forming processes operate from the surface downward – Horizons – zones or layers of soil Soil Profile
- 26. © 2015 Pearson Education Ltd. • Horizons in temperate regions – O – organic matter – A – organic and mineral matter – E – little organic matter • Eluviation • Leaching – B – zone of accumulation – C – partially altered parent material Soil Profile
- 27. © 2015 Pearson Education Ltd. • Topsoil – Zones O and A together • Solum – “True soil” – O, A, E, B together Soil Profile
- 28. © 2015 Pearson Education Ltd. Soil Horizons
- 29. © 2015 Pearson Education Ltd. Contrasting Soil Profiles
- 30. © 2015 Pearson Education Ltd. • Classifying soils – System for classifying soils in the United States is called the Soil Taxonomy • Emphasizes physical and chemical properties of the soil profile • Names of the soil units are combinations of syllables of Latin and Greek origin Soil
- 31. © 2015 Pearson Education Ltd. Global Soil Regions
- 32. © 2015 Pearson Education Ltd. • Recycling of Earth materials • Natural rates of erosion depend on – Soil characteristics – Climate – Slope – Type of vegetation Soil Erosion
- 33. © 2015 Pearson Education Ltd. Soil Erosion • Processes that erode soil – Water erosion • Raindrops dislodge soil particles • Flowing water carries soil away • 2/3 of all U.S. soil erosion – Wind Erosion • Occurs with dry soil conditions
- 34. © 2015 Pearson Education Ltd. • Soil erosion and sedimentation can cause – Reservoirs to fill with sediment – Contamination by pesticides and fertilizers Soil Erosion
- 35. © 2015 Pearson Education Ltd. Soil Erosion
- 36. © 2015 Pearson Education Ltd. • Controlling soil erosion – Leave steep slopes undisturbed – Terrace crop planting – Grassed waterways – Tree windbreak barriers Soil Erosion
- 37. © 2015 Pearson Education Ltd. Soil Conservation
- 38. © 2015 Pearson Education Ltd. Soil Conservation: Grassed Waterway
- 39. © 2015 Pearson Education Ltd. • The downslope movement of rock, regolith, and soil under the direct influence of gravity • Gravity is the controlling force Mass Wasting
- 40. © 2015 Pearson Education Ltd. Mass Wasting Triggers • Saturation of the material with water – Destroys particle cohesion – Water adds weight
- 41. © 2015 Pearson Education Ltd. Mass Wasting Triggers • Oversteepening of slopes – Unconsolidated granular particles assume a stable slope called the angle of repose – Stable slope angle is different for various materials
- 42. © 2015 Pearson Education Ltd. Mass Wasting Triggers • Removal of anchoring vegetation • Ground vibrations from earthquakes
- 43. © 2015 Pearson Education Ltd. • Generally each type is defined by – The material involved – debris, mud, earth, or rock – The movement of the material • Fall (free-fall of pieces) • Slide (material moves along a well-defined surface) • Flow (material moves as a viscous fluid) Mass Wasting Processes
- 44. © 2015 Pearson Education Ltd. • Generally each type is defined by – The rate of the movement • Fast • Slow Mass Wasting Processes
- 45. © 2015 Pearson Education Ltd. Mass Wasting Forms • Slump – Rapid movement along a curved surface – Occur along oversteepened slopes
- 46. © 2015 Pearson Education Ltd. Mass Wasting Forms • Rockslide – Rapid – Blocks of bedrock move down a slope
- 47. © 2015 Pearson Education Ltd. Mass Wasting Forms • Debris flow (mudflow) – Rapid flow of debris with water – Often confined to channels – Debris flows composed mostly of volcanic materials are called lahars
- 48. © 2015 Pearson Education Ltd. Mass Wasting Forms • Earthflow – Rapid – Typically occur on hillsides in humid regions – Water saturates the soil – Liquefaction – a special type of earthflow sometimes associated with earthquakes
- 49. © 2015 Pearson Education Ltd. • Creep – Slow movement of soil and regolith downhill – Causes fences and utility poles to tilt • Solifluction – Slow movement in areas underlain by permafrost – Upper (active) soil layer becomes saturated and slowly flows over a frozen surface below Mass Wasting Forms
- 50. © 2015 Pearson Education Ltd. Creep
- 51. © 2015 Pearson Education Ltd. Solifluction