Mass Movement

4,966 views

Published on

Grade 12. Geomorphology. SA curriculum. Slope forms.

Published in: Education, Technology, Travel
  • Be the first to comment

Mass Movement

  1. 1. Learning objectives Grade 12 Geomorphology Mass Movement Slope forms: crest, free face, talus and pediment. Mass Movement Creep Slump Debris flow Earth flow Rockslides Human Land use and Landslides Preventing Landslides
  2. 2. Slopes Figure 9.3
  3. 3. Talus Slope Free Face Pediment Crest      Accumulation of active degrees Steep slope of half to from free Gentle slope Convexslopewith debris5erosion face Slope Upland Bare rock face Concave slope Initial angel of 35-37 degrees Large boulders near cliff face, pebbles rills Rainwater channelled into Talus slope and stones further away result in a Covered by and from the Weatheringfinessoil creep gullies called more gentlematerial falls is easily washedthe cliff face to retreat Erosion, slumping and weathering cliff Unconsolidated material over the cause away. Weathered angle Small particles called FINES washed out onto the pediment
  4. 4. Identify the following slope and list 4 characteristics of this slope in a textbox below. Talus Slope at Wheeler Peak, Great Basin National Park, Nevada. Accumulation of debris from free face. Slope angle of 35-37 degrees. Large boulders near cliff face, pebbles and stones further away result in a more gentle angle. Small particles called fines are. washed out onto the pediment. Source: Tom Bean/DRK Photos Copyright © Houghton Mifflin Company. All rights reserved. Geology, 13a–4
  5. 5. Identify this slope and list 4 characteristics of the slope. Free Face :Steep slope with active erosion. Bare rock face. Rainwater channelled into gullies called rills. Erosion, weathering and slumping cause the cliff face to retreat. Fig. 11-8b, p. 253
  6. 6. Learning objectives Grade 12 Geomorphology Mass Movement Slope forms: crest, free face, talus and pediment. Mass Movement Creep Slump Debris flow Earth flow Rockslides Human Land use and Landslides Preventing Landslides
  7. 7. Mass Movement Soil Creep Solifluction Earth and Mud flows Landslides and Rockfalls Source: Roger J. Wyan/AP Wide World Photo Copyright © Houghton Mifflin Company. All rights reserved. Geology, 13a–7
  8. 8. Mass Movement 1 Mass wasting is the downslope movement of Earth material due to gravity. Factors such as slope angle, weathering and climate, water content, vegetation, and overloading are interrelated, and all affect mass wasting. 2 Mass movements can be triggered by such factors as soil saturation and ground shaking. 3 Mass wasting can be categorized as resulting from either rapid mass movements or slow mass movements. 4 The different types of rapid mass movements are rockfalls, rock slides, mudflows, debris flows, and some slumps; each type has recognizable characteristics. 5 The different types of slow mass movements are earthflows, solifluction, soil creep, and some slumps; each type has recognizable characteristics. 6 People can minimize the effects of mass wasting by conducting geologic investigations of an area and stabilizing slopes to prevent and ameliorate movement.
  9. 9. Table 11-2, p. 252
  10. 10. Important types of mass wasting • Slide – downslope movement of coherent block of earth material • Slump – is sliding along a curved slip plane producing slump blocks • Fall – rocks fall from vertical face • Flow – Downslope movement of unconsolidated material in which particles move about and mix within the mass • Subsidence is the sinking of of a mass of earth material below the level of surrounding material
  11. 11. Factors Affecting Slope Stability • • • • • • Type of earth material Slope Angle and Topography Climate Vegetation Water Time
  12. 12. Triggers for rapid Mass Wasting • Rain • Oversteepening – cutting at foot of slope – piling on head of slope • Deforesting / Devegetating • Earthquakes
  13. 13. Some Common Processes that Oversteepen Slopes Copyright © Houghton Mifflin Company. All rights reserved. Geology, 13a–13
  14. 14. Some Common Processes that Oversteepen Slopes (cont’d) Copyright © Houghton Mifflin Company. All rights reserved. Geology, 13a–14
  15. 15. Some Common Processes that Oversteepen Slopes (cont'd) Copyright © Houghton Mifflin Company. All rights reserved. Geology, 13a–15
  16. 16. Learning objectives Grade 12 Geomorphology Mass Movement Slope forms: crest, free face, talus and pediment. Mass Movement Creep Slump Debris flow Earth flow Rockslides Human Land use and Landslides Preventing Landslides
  17. 17. Creep • very slow downslope movement of soil • result of freezing and thawing
  18. 18. Creep from D. Schwert, NDSU
  19. 19. Creep
  20. 20. Fig. 11-5a, p. 249
  21. 21. Fig. 11-5c, p. 249
  22. 22. Fig. 11-5d, p. 249
  23. 23. Fig. 11-6, p. 249
  24. 24. Fig. 11-2, p. 247
  25. 25. Learning objectives Grade 12 Geomorphology Mass Movement Slope forms: crest, free face, talus and pediment. Mass Movement Creep Slump Debris flow Waters role in mass movement Earth flow Rockslides Human Land use and Landslides Preventing Landslides
  26. 26. Slump A slump is a type of slope failure in which a downward and outward rotational movement of rock or regolith occurs along a curved concave-up surface. – Often the result of artificial modification of the landscape. – Associated with heavy rains or sudden shocks, such as earthquakes.
  27. 27. Slump (a type of slide) • Indicators: – Scarp – “Hummocky” terrain on and below (earthflow)
  28. 28. Slump scarp
  29. 29. Learning objectives Grade 12 Geomorphology Mass Movement Slope forms: crest, free face, talus and pediment. Mass Movement Creep Slump Debris / Mud flow Earth flow Rockslides Human Land use and Landslides Preventing Landslides
  30. 30. Debris Flow • Debris flows are the downslope flow of relatively coarse material • > 50% of particles in a debris flow are coarser than sand • Movement may be very slow or very fast, depending on topographic conditions • Contain less water and larger particles than Mudflows. Turtle Mountain Rock Fall Turtle Mountain
  31. 31. Water's Role In Mass Movement Fig. 11-7a, p. 251
  32. 32. Water's Role In Mass Movement Fig. 11-7b, p. 251
  33. 33. Water's Role In Mass Movement: Before Slide Copyright © Houghton Mifflin Company. All rights reserved. Geology, 13a–33
  34. 34. Water's Role In Mass Movement: After Slide Copyright © Houghton Mifflin Company. All rights reserved. Geology, 13a–34
  35. 35. Parallel Planes: Mass-Movement Potential Copyright © Houghton Mifflin Company. All rights reserved. Geology, 13a–35
  36. 36. Learning objectives Grade 12 Geomorphology Mass Movement Slope forms: crest, free face, talus and pediment. Mass Movement Creep Slump Debris flow Waters role in mass movement Earth flow Rockslides Human Land use and Landslides Preventing Landslides
  37. 37. Earthflow
  38. 38. Learning objectives Mass Movement Slope forms: crest, free face, talus and pediment. Mass Movement Creep Slump Debris flow Waters role in mass movement Earth flow Rockslides Human Land use and Landslides Preventing Landslides
  39. 39. Rockslide • Rock moves because there’s nothing holding it back! • Generally requires a pre-existing low-friction surface...
  40. 40. Rockslide • like a clay layer, once it’s wet...
  41. 41. Fig. 11-8a, p. 253
  42. 42. Fig. 11-8b, p. 253
  43. 43. Learning objectives Mass Movement Slope forms: crest, free face, talus and pediment. Mass Movement Creep Slump Debris flow Waters role in mass movement Earth flow Rockslides Human Land use and Landslides Preventing Landslides
  44. 44. Human Land Use and Landslide • Urbanization, irrigation • Timber harvesting in weak, relatively unstable areas • Artificial fillings of loose materials • Artificial modification of landscape • Dam construction
  45. 45. Learning objectives Grade 12 Geomorphology Mass Movement Slope forms: crest, free face, talus and pediment. Mass Movement Creep Slump Debris flow Waters role in mass movement Earth flow Rockslides Human Land use and Landslides Preventing Landslides
  46. 46. Mitigating the Landslide Hazard (2) • Preventing landslides – Drainage control: Reducing infiltration and surface runoff – Slope grading: Reducing the overall slope – Slope supports: Retaining walls or deep supporting piles • Avoid landslide hazards – Landslide warning for critical evacuations – Correcting landslides
  47. 47. Fig. 11-23a, p. 265
  48. 48. Fig. 11-23b, p. 265
  49. 49. Fig. 11-24b, p. 265
  50. 50. 1 4 2 5 3 6
  51. 51. A slump is a type of slope failure in which a downward and outward rotational movement of rock or regolith occurs along a curved concave-up surface. – Often the result of artificial modification of the landscape. – Associated with heavy rains or sudden shocks, such as earthquakes. Identify this type of Mass Wasting and explain how it occurs.
  52. 52. What can be done to minimize damage from Rockfalls? Use the photographs to assist you in your answer. Minimizing damage from rockfalls. (a) Wire mesh covers this steep slope in Hawaii. This is a common practice in mountainous areas to prevent rocks from falling on the road. (b) A wire mesh fence along the base of this hillside of Highway 44 in California has caught many boulders and prevented them from rolling onto the highway. But note that some boulders have made it over the fence.
  53. 53. Identify this type of mass wasting and explain what causes it to occur! • Creep is extremely slow downward movement of dry surfacial matter. • Movement of the soil occurs in regions which are subjected to freezethaw conditions. The freeze lifts the particles of soil and rocks and when there is a thaw, the particles are set back down, but not in the same place as before.
  54. 54. Identify the following types of Mass wasting and tabulate the causes of each. Rockslide Occurs where nothing is holding the rocks back. Generally requires a pre-existing low-friction surface, like a clay layer once its wet. Landslide Caused by: Erosion causing extremely steep slopes A powerful earthquake Excess weight on unstable soil A Volcanic eruption.
  55. 55. 1) Identify this type of mass wasting 2) What must you do to prevent this type of mass wasting? MUDFLOW • • • Plant ground cover on slopes and build retaining walls. In mudflow areas, build channels or deflection walls to direct the flow around buildings. Install flexible pipe fittings to avoid gas or water leaks.
  56. 56. 1) Identify this type of mass wasting 2) Where does this type of mass mostly occur? Solifluction • the slow downslope movement of watersaturated sediment • most common in areas of permafrost.
  57. 57. Schuters pg 204 and 205

×