Mass Movement

Grade 12. Geomorphology. SA curriculum. Slope forms.

1. Learning objectives Slope forms: crest, free face, talus and pediment. Mass Movement Creep Slump Debris flow Earth flow Rockslides Human Land use and Landslides Preventing Landslides Grade 12 Geomorphology Mass Movement

2. Slopes Figure 9.3

3. Crest Convex slope Initial Upland Weathering and soil creep Weathered material falls over the cliff Free Face Steep slope with active erosion Bare rock face Rainwater channelled into gullies called rills Erosion, slumping and weathering cause the cliff face to retreat Talus Slope Accumulation of debris from free face Slope angel of 35-37 degrees Large boulders near cliff face, pebbles and stones further away result in a more gentle angle Small particles called FINES washed out onto the pediment Pediment Gentle slope of half to 5 degrees Concave slope Covered by fines from the Talus slope Unconsolidated material is easily washed away.

4. Copyright © Houghton Mifflin Company. All rights reserved. Geology , 13a – 4 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 Identify the following slope and list 4 characteristics of this slope in a textbox below.

5. Fig. 11-8b, p. 253 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.

6. Learning objectives Slope forms: crest, free face, talus and pediment. Mass Movement Creep Slump Debris flow Earth flow Rockslides Human Land use and Landslides Preventing Landslides Mass Movement Grade 12 Geomorphology

7. Copyright © Houghton Mifflin Company. All rights reserved. Geology , 13a – 7 Soil Creep Solifluction Earth and Mud flows Landslides and Rockfalls Source: Roger J. Wyan/AP Wide World Photo Mass Movement

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. Table 11-2, p. 252

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. Factors Affecting Slope Stability Type of earth material Slope Angle and Topography Climate Vegetation Water Time

12. Triggers for rapid Mass Wasting Rain Oversteepening cutting at foot of slope piling on head of slope Deforesting / Devegetating Earthquakes

13. Copyright © Houghton Mifflin Company. All rights reserved. Geology , 13a – 13 Some Common Processes that Oversteepen Slopes

14. Copyright © Houghton Mifflin Company. All rights reserved. Geology , 13a – 14 Some Common Processes that Oversteepen Slopes (cont’d)

15. Copyright © Houghton Mifflin Company. All rights reserved. Geology , 13a – 15 Some Common Processes that Oversteepen Slopes (cont'd)

16. Learning objectives Slope forms: crest, free face, talus and pediment. Mass Movement Creep Slump Debris flow Earth flow Rockslides Human Land use and Landslides Preventing Landslides Mass Movement Grade 12 Geomorphology

17. Creep very slow downslope movement of soil result of freezing and thawing

18. Creep from D. Schwert, NDSU

19. Creep

20. Fig. 11-5a, p. 249

21. Fig. 11-5c, p. 249

22. Fig. 11-5d, p. 249

23. Fig. 11-6, p. 249

24. Fig. 11-2, p. 247

25. Learning objectives 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 Mass Movement Grade 12 Geomorphology

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. Slump (a type of slide) Indicators: Scarp “Hummocky” terrain on and below (earthflow)

28. Slump scarp

29. Learning objectives 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 Grade 12 Geomorphology Mass Movement

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 Turtle Mountain Rock Fall

31. Fig. 11-7a, p. 251 Water's Role In Mass Movement

32. Fig. 11-7b, p. 251 Water's Role In Mass Movement

33. Copyright © Houghton Mifflin Company. All rights reserved. Geology , 13a – 33 Water's Role In Mass Movement: Before Slide

34. Copyright © Houghton Mifflin Company. All rights reserved. Geology , 13a – 34 Water's Role In Mass Movement: After Slide

35. Copyright © Houghton Mifflin Company. All rights reserved. Geology , 13a – 35 Parallel Planes: Mass-Movement Potential

36. Learning objectives 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 Mass Movement Grade 12 Geomorphology

37. Earthflow

38. Learning objectives 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 Mass Movement

39. Rockslide Rock moves because there’s nothing holding it back! Generally requires a pre-existing low-friction surface...

40. Rockslide like a clay layer, once it’s wet...

41. Fig. 11-8a, p. 253

42. Fig. 11-8b, p. 253

43. Learning objectives 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 Mass Movement

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. Learning objectives 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 Mass Movement Grade 12 Geomorphology

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. Fig. 11-23a, p. 265

48. Fig. 11-23b, p. 265

49. Fig. 11-24b, p. 265

50. 1 2 3 4 5 6 Answer these questions !

51. Identify this type of Mass Wasting and explain how it occurs. 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.

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. Creep is extremely slow downward movement of dry surfacial matter. Movement of the soil occurs in regions which are subjected to freeze-thaw 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. Identify this type of mass wasting and explain what causes it to occur!

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. 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. 1) Identify this type of mass wasting 2) Where does this type of mass mostly occur? Solifluction the slow downslope movement of water-saturated sediment most common in areas of permafrost.

57. Schuters pg 204 and 205