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Landslides, Part 2

Landslides, Part 2. Beverly Hills slide, Feb 2005. Outline. Slide examples Flows Avalanches. Block Slide. The rapid movement of large blocks of detached bedrock sliding more or less as a unit. Block Slide. Debris Slide.

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Landslides, Part 2

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  1. Landslides, Part 2 Beverly Hills slide, Feb 2005

  2. Outline • Slide examples • Flows • Avalanches

  3. Block Slide The rapid movement of large blocks of detached bedrock sliding more or less as a unit.

  4. Block Slide

  5. Debris Slide Rock material and soil move largely as one or more units along planes of weakness.

  6. Debris Slide

  7. 1925 Gros Ventre Slide, Wyoming

  8. 1925 Gros Ventre Slide, Wyoming

  9. 1925 Gros Ventre Slide, Wyoming

  10. 1925 Gros Ventre Slide, Wyoming

  11. 1925 Gros Ventre Slide, Wyoming

  12. 1925 Gros Ventre Slide, Wyoming

  13. Gros Ventre Slide, Wyoming

  14. Vaiont Reservoir Slide Debris slide caused reservoir wall to collapse, sent water downstream Fig. 12.17

  15. Lateral Spreading

  16. Turnagain Heights, Alaska

  17. Flows • Mass movements behave like fluids • Materials include boulders, sand, ice, mix • Speed varies - barely moving to ~200 mph • Various types of flow, depending on material, slip surface

  18. Loess Flow • Dry flows of fine silt deposits • Example: 1920 China • 160 by 275 km hill of loess flowed after earthquake • Killed ~200,000 people by burying villages very rapidly

  19. Earth Flow • A fluid movement of relatively fine-grained material (soils, clays)

  20. Earthflow

  21. Debris Flow • A fluid mass movement of rock fragments supported by a muddy matrix. May move a speeds of up to 100 km/hr!

  22. Mudflow • A flowing mass of material (mostly finer than sand, along with some rock debris) containing a large amount of water. • May travel large distances and high speeds • Can carry particles as large as a house!

  23. Debris Avalanche • Fast (up to 280 km/hr) downhill movements of soil and rock, usually occurring in humid mountainous regions

  24. Mountain region in Peru, before a Mw 7.7 occurred in the subduction zone offshore Mt Huascaran, Peru (before 1970)

  25. Mt Huascaran, Peru (after 1970)

  26. Combination of Processes: Mt. Huascaran

  27. Snow Avalanches • Snow has same pull from gravity • Can fail in creep, fall, slide, flow • Snowfall, wind-blown snow load slope towards failure • Also skiers

  28. Snow Avalanche • Large events - slab of snow breaks away • Occurs because each layer of snow has different properties • Layers deposited at different times, vary in strength, hardness, density, thickness

  29. Snow! Can travel at very high speeds, trapping skiers

  30. Ways to Reduce Losses Due to Landslides Include: • Avoid construction in areas prone to mass movement • Build in a way that does not make naturally stable slope unstable • Engineer water drainage to prevent strata to become water saturated and prone to fail

  31. Note dipping beds undercut by excavation for house

  32. Failure occurs when water-saturated strata slide along slippery clay unit, breaching thin retaining wall Box 12.1

  33. Submarine Movements • Same types of failures occur underwater • Example: Hawaii has significant slumps, debris avalanches • Volcanic flank collapse - whole side of volcano falls off • Leads to tsunami

  34. Hawaii

  35. Big Island, Hawaii • Motion along blocks near Kilauea today!

  36. Next Time • Subsidence and review for midterm

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