1. Mass Movements

2. Smith Chapter 8

5. Mass Movements Downslope movement of large volumes of surface materials under gravity

6. Mass Movements Vary in speed –rapid movements can kill –slower movements can be costly soil creep, subsidence

7. Mass Movements Vary in materials –Landslides Rockfalls Mudflows –Avalanches

8. Mass Movements Triggered –weather –earthquake, volcano –vibration

9. Mass Movements Risk increasing as land-hunger forces development of unstable & steep slopes

10. Germi, Iran

14. Mass Movements Early 1970s: produced around 600 deaths/year Late 1980s: several thousand annually Most deaths in Third World –USA: annual death toll 25-30

16. Mass Movements Annual losses in the billions US$ each year –especially in cities US$1-3 bn/year in the USA –Appalachian, Rocky Mtns, Pacific US$500 million in LA area from landslides in an el Nino year

17. Mass Movements Most deaths on Pacific Rim –associated with seismic activity –high population densities –heavy typhoon rainfall –rapid economic development

18. Mass Movements Increased by shanty-town settlement –on steeper, less-stable slopes

19. Caracas, Venezuela 1950s: fewer than 1 urban landslide/year City expands rapidly, esp. in 1970s Shanties spread out onto hills 1980s: 35-40 urban landslides/year

20. High landslide hazard: Guatemala City

21. La Paz, Bolivia

25. Avalanches Common on snow-covered slopes steeper than 20 degrees, less than 60 degrees Move at 80m/s (288 km/h) Settlement needs to avoid the runout tracks

26. Avalanches Frequent but usually harmless –USA 7,000-10,000 avalanches/year, only 1% cause harm Threat to unwary travellers, badly-sited settlements Risks increased by alpine tourism development

27. Lake Tahoe CA

28. Avalanches More avalanche deaths in Europe –higher population density –Switzerland 25-30 deaths/year

31. Intense Landslide Risk High mountains –Areas of seismic shaking –High relief Soils made erodible by deforestation Thick deposits of fine-grained loosely- packed material Areas of high rainfall

33. Ganges delta

34. Unstable slopes, Nepal

35. Rohtang pass, India

39. Auguas Calientes, Peru

40. Rail line serving Maccu Piccu

41. Huascaran Peru

42. Monument to the dead of Yungay

43. Yungay school bus

44. Frank Slide AB, 1903 Rockfall caused by natural weathering of anticlinal rocks of Turtle Mountain Triggered by spring freeze-thaw Undercut by mining Destroyed Frank townsite Killed 70

45. Frank slide AB

48. Hope slide BC

51. Soil Mechanics Slopes fail when shear strength of slope is exceeded –excessive loading –cohesion failure of slope materials

52. Soil Mechanics Different configurations of slide –rotational –translational

53. Lake Merced 1967

55. Ground subsidence

56. Debris flows Slope materials become fluidised –saturated –follows natural drainage channels –great destructive force Very common in the wet tropics

60. China: Guangxi

62. Brazil 1991: 15 killed

63. Bhutan after monsoon

67. NZ west coast

68. NZ landslide hazard

69. How to trigger a landslide Make slope steeper –undercut it –add material Add weight to the slope Add water to the slope (very effective) Remove vegetation Provide vibrations and shocks

70. Aberfan 1966 Coal-mine waste dump collapses on Welsh village Destroyed several homes and primary school during morning assembly Killed 140+, –including 111 children

74. Aberfan 1966 Hazard noted in 1920s Mine dump not engineered Receiving wet slurry in 1966 Village and primary school in harm’s way School principal had complained of the dangers, her protests were ignored

75. Reducing landslide risks Careful settlement siting Slope stabilisation Slope drainage modification Slope vegetation Revetments, slope freezing (temporary)

78. Reducing avalanche risks Trigger avalanches at safe times –smaller avalanches –with explosives, artillery Defensive structures Careful settlement siting

79. Avalanche defences