1. WHY DO HILLSLOPES MOVE AT SOME TIMES AND NOT AT OTHERS? Forces, Resistances and Thresholds

2. FORCESRESISTANCES IF FORCE GREATER THAN RESISTANCE, HILLSIDE MOVES OR “FAILS”. IF RESISTANCE GREATER THAN FORCE, HILLSIDE IS STABLE.

3. FORCE = MASS X ACCELERATION

4. 1. MASS IS THE MASS OF THE HILLSIDE MATERIAL!

5. FORCE = MASS X ACCELERATION 1. MASS IS THE MASS OF THE HILLSIDE MATERIAL! 2. ACCELERATION? ……….

6. FORCE = MASS X ACCELERATION 1. MASS IS THE MASS OF THE HILLSIDE MATERIAL! 2. ACCELERATION? ……… DOWNSLOPE MOVEMENT UNDER THE INFLUENCE OF GRAVITY …… ACCELERATION DUE TO GRAVITY.

7. ACCELERATION DUE TO GRAVITY ACTS PERPENDICULARLY.

8. INTRODUCE A HORIZONTAL SLOPE, 0°. 0°

9. W PLACE BLOCK OF EARTH MATERIAL, WEIGHT, W, ON THE SLOPE 0°

10. W ARBITRARILY DEFINE “DOWNSLOPE” AS TO THE LEFT.

11. W 0° NONE OF THE FORCE OF GRAVITY IS ACTING IN THE DOWNSLOPE DIRECTION

12. W 0° INCLINE THE PLANE TO 30° W 30°

13. W 0° W 30° DOWNSLOPE DIRECTION NOW CLOSER TO DIRECTION OF GRAVITY

14. W 0° INCLINE THE PLANE TO 60° W 30° W 60°

15. W 0° W 30° W 60° DOWNSLOPE DIRECTION EVEN CLOSER TO DIRECTION OF GRAVITY

16. W 0° W 30° W 60° W 90° INCLINE PLANE TO THE VERTICAL, 90°

17. W 0° W 30° W 60° W 90° ALL OF GRAVITY NOW ACTING IN THE DOWNSLOPE DIRECTION.

18. W 0° W 30° W 60° W 90° PROPORTION OF ACCELERATION DUE TO GRAVITY ACTING IN THE DOWNSLOPE DIRECTION IS INCREASING.

19. W 0° W 30° W 60° W 90° SIN(0°) = 0 0 X W.g

20. W 0° W 30° W 60° W 90° SIN(0°) = 0 0 X W.g SIN(30°) = 0.5 0.5 X W.g

21. W 0° W 30° W 60° W 90° SIN(0°) = 0 0 X W.g SIN(30°) = 0.5 0.5 X W.g 0.87 X W.g SIN(60°) = 0.87

22. W 0° W 30° W 60° W 90° SIN(0°) = 0.0 0.0 X W.g SIN(30°) = 0.5 0.5 X W.g 0.87 X W.g SIN(60°) = 0.87 SIN(90°) = 1.0 1.0 X W.g

24. Mean slope-angle frequency distribution and size frequency distribution of landslide masses in Higashikubiki area, Japan. Junko Iwahashi, Shiaki Watanabe and Takahiko Furuya Geomorphology Volume 50, Issue 4Geomorphology Volume 50, Issue 4, 1 March 2003, Pages 349-364

26. WHY WOULD FORCES ON A HILLSIDE FLUCTUATE?

27. WHY WOULD FORCES ON A HILLSIDE FLUCTUATE? 1. Changes in Weight2. Changes in Slope

28. WHY WOULD FORCES ON A HILLSIDE FLUCTUATE? 1. Changes in Weight Add water to slope – fill pore spaces 62 lbs per cu ft. 8 lbs per gallon Nevado del Ruiz, Colombia. Sichuan Province, China. Armero, Colombia.

29. http://www.ibtimes.co.uk/floods-chile- landslides-peru-after-heaviest-rain-80-years- 1493792

30. WHY WOULD FORCES ON A HILLSIDE FLUCTUATE? 1. Changes in Weight Add water to slope – fill pore spaces Build on it! Bournemouth, England Saskatoon, Canada

31. WHY WOULD FORCES ON A HILLSIDE FLUCTUATE? 2. Changes in Slope Erosion of bottom of slope. Devon, England Colorado, US

32. WHY WOULD FORCES ON A HILLSIDE FLUCTUATE? 2. Changes in Slope Erosion of bottom of slope. Road/rail cuttings. Thailand Virginia

33. WHAT ARE THE RESISTANCES TO MOTION ON A HILLSIDE? 1.Normal Stress : “Normal” meaning at right angles to (the slope). Stress implies the component of the acceleration due to gravity, NOT, acting in a downslope direction, but actually holding the hillside in place.

34. W 0° WHAT IS NORMAL STRESS ? Downslope Normal Stress

35. W 30° Downslope Component: Approaches gravity as slope increases. Normal Stress: Moves away from gravity (decreases) as slope increases.

36. W 30° Downslope Component: Approaches gravity as slope increases. Normal Stress: Moves away from gravity (decreases) as slope increases. N.S = Cos (Slope). W. g.

37. WHAT ARE THE RESISTANCES TO MOTION ON A HILLSIDE? 1.Normal Stress: Cosine Slope. 2.Friction: Degree to which particles lock together and resist movement.

38. Angle of internal friction (repose)

39. GENERALLY: Big grains High friction Small grainsLow friction

40. WHAT ARE THE RESISTANCES TO MOTION ON A HILLSIDE? 1.Normal Stress: Cosine Slope. 2.Friction: High for big grains, low for small. 3.Cohesion: The force that holds together molecules or like particles within a soil.

41. Cohesion GENERALLY: ClaysHigh cohesion Large grainsLow cohesion

42. FORCESRESISTANCES 1.Weight 2.Slope 1.Normal Stress 2.Friction 3.Cohesion

43. FORCESRESISTANCES 1.Weight 2.Slope 1.Normal Stress 2.Friction 3.Cohesion WATER HAS DIFFERING ROLES IN THE BALANCE DEPENDING UPON THE QUANTITY OF WATER PRESENT.

44. HYGROSCOPIC WATER

45. FORCESRESISTANCES 1.Weight 2.Slope 1.Normal Stress 2.Friction 3.Cohesion HYGROSCOPIC No Role Vs.

46. CAPILLARY WATER

47. FORCESRESISTANCES 1.Weight 2.Slope 1.Normal Stress 2.Friction 3.Cohesion CAPILLARY Resistance Negative Pore Water Pressures Vs.

48. FREE or GRAVITATIONAL WATER

49. FORCESRESISTANCES 1.Weight 2.Slope 1.Normal Stress 2.Friction 3.Cohesion GRAVITATIONAL Force Positive Pore Water Pressures Vs.

50. Mass Movement Experiment for Floridians

51. Sand Castle – Steep Slopes

52. Mass Movement Experiment for Floridians Move up the beach

53. Mass Movement Experiment for Floridians Move down the beach

54. Mass Movement Experiment for Floridians Same sand, same bucket, same slope angle! Slope holds!Slope collapses!

55. Mass Movement Experiment for Floridians The Difference – Water Content! Slope holds!Slope collapses! Capillary Water Resistance! Hygroscopic Water Neutral! Free Water Force!

56. FORCESRESISTANCES 1.Weight 2.Slope 1.Normal Stress 2.Friction 3.Cohesion Vs. ExtrinsicIntrinsic

57. Time Force and Resistance

58. Time Force and Resistance Water is universal solvent, ultimately breaking down strength of rocks along with other processes

59. Time Force and Resistance Forces often fluctuate with presence of water (rain storms or seasonal snowmelt).

60. Time Force and Resistance Resistance > Force Stable Slope

61. Time Force and Resistance Resistance > Force Stable Slope

62. Time Force and Resistance Resistance > Force Stable Slope Force> Resistance SLOPE FAILURE!

63. Time Force and Resistance Resistance > Force Stable Slope Resistances ?

65. 1. Downslope movement decreases elevation of uplands, increases elevation of valley – decreases slope, increases normal stress (resistance).

66. 2. Downslope movement exposes unweathered, “strong” rock, with greater friction and cohesion - increases resistance.

67. Time Force and Resistance Resistance > Force Stable Slope Resistance > Force Stable Slope