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What is Mass Wasting?

What is Mass Wasting?. Rapid types Slow types. Selected Landslides. DATE LOCATION TYPE DEATHS 1556 China Landslides-earthquake triggered 1,000,000 1806 Switzerland Rock slide 457 1920 China (Kansu) Landslides-earthquake triggered 200,000

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What is Mass Wasting?

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  1. What is Mass Wasting? Rapid types Slow types

  2. Selected Landslides DATELOCATIONTYPE DEATHS 1556 China Landslides-earthquake triggered 1,000,000 1806 Switzerland Rock slide 457 1920 China (Kansu) Landslides-earthquake triggered 200,000 1963 Italy (Vaiont Dam) Landslide-subsequent flood 2,000 1966 U. K. (Wales) Debris flow-collapse of mining-waste 144 1970 Peru (Mt. Huascaran) Rockfall & debris avalanche 25,000  earthquake triggered 1972 USA (WV) Landslide & mudflow-collapse of 400 mining-waste 1979 Indonesia (Sumatra) Landslide 80 1980 USA (Washington) Avalanche and mudflow 63 1989 Tadzhikistan Mudflow-earthquake triggered 274 1996 Brazil (Recife) Mudflow 49 1999 Venezuela Mudflow 10,000

  3. Why Should You Study Mass Wasting?

  4. 3 Factors Influencing Mass Wasting: • Shear strength of slope mat. • Angle of repose • Gravity

  5. Gravitational forcesexceedresisting forces Dynamic equilibrium

  6. 5 Causes of Mass Wasting:

  7. Slope Angle {Steep slope = _________ stability} • Oversteepening slopes:

  8. Highway excavations remove support often resulting in slope failure. Pan-American Highway, Mexico

  9. Weathering & Climate • Weathering decomposes & disintegrates rock, ____________shear strength & ____ mass wasting. • Mass movement ______________ in deeply weathered material. (prevalent in tropics) • Deserts Lack of vegetation (_______________) & cloudbursts frequently produce rapid mass wasting (i.e., mudflows).

  10. Water Content Slope stability  How does water affect slope stability?

  11. Vegetation Golden State Freeway,1987

  12. Overloading… • Under natural conditions, a slope’s load is supported by friction of grain-to-grain contacts w/in slope material. • Overloading __________________________________ w/in slope material. • Dec. shear strength

  13. Triggering Mechanisms Most common: In highly unstable slopes: La Conchita, Ca.1995

  14. Types of Mass Movements Falls Rockfalls Slides Slump Rockslides Flows Mudflow Debris flow Earthflow Creep Complex movements

  15. Rockfalls: (_________________________) Slopes are sometimes covered w/ wire mesh to reduce the hazard. Hawaii

  16. A B Slides Slumps Rock slides

  17. Flows Earthflows Baraga, Michigan

  18. Mudflows Debris flows Estes Park, Colorado

  19. Creep Effects: Marathon, TX

  20. Complex movements {combo of several types} Debris avalanches  1970  killed 25,000 in Yungay & Ranrahirca Peru, 1970

  21. Recognize & Minimize Effects of Mass Movement • Geologic investigation identifies • Analysis of a material’s properties (composition, susceptibility to weathering, cohesiveness, & ability to transmit fluids) (Info is used to assess risks before construction begins.)

  22. Dewatering Ways to dewater: • Perforated drainpipes inserted horizontally into slopes are used to reduce the amt of water w/in slope material. Pt. Fermin, CA

  23. How Can We Minimize Mass Movement? Cut-and-Fill method

  24. How Can We Minimize Mass Movement? Benching

  25. How Can We Minimize Mass Movement? Retaining walls Most successful when:

  26. How Can We Minimize Mass Movement? Rock bolts Brisbane, Aust..

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