Landslides

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Landslides
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Mass Wasting

• Downslope movement of earth materials
• Generally gravity driven
• Generally result from undercutting of a slope
• Either natural or human induced
• Landslides
• General term for all types of mass wasting

Not to be confused with mass wasted
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Landslide Factors

• Steepness of slope
• Steep slopes are generally unstable
• Vegetation
• Roots hold soil together and absorb water
• Vegetated slopes generally more unstable than
  non-vegetated

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Landslide Factors Continued...

• Water
• Sandcastle analogy
• Nature of unconsolidated stuff
• Angle of reposemaximum slope at which loose
  material remains stable
• Higher for angular rocks

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Landslide Factors Continued...

• Type of rock and orientation of rock layers
• Sedimentary rocks dipping in same direction of
  slope bad
• Sedimentary rocks dipping in the opposite
  direction of slope good

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Landslide Factors Continued...

• Earthquakes and volcanoes
• Earthquakes can destabilize slopes
• A volcanic eruption can melt glaciers at
  summitcreating a landslide

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Youre just my type.

• Flow
• Loose, unconsolidated sediment/soil moves in a
  fluid-like way
• Slide
• Movement of a coherent block of material along a
  fracture
• Fall
• Rapid, free-fall motion

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Types of Mass Wasting
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Flows
Natural creep

• Creep
• Slow downhill flow of rock or soil under the
  influence of gravity
• Very slow1cm/yr
• Shallow stuff moves more quickly than deeper
  stuff
• Pistol butt trees and leaning fences

Human creep
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Flows mudflows

• A flow composed entirely of fine-grained sediment
• Lobe shaped deposits
• Can be wicked fast60mph
• Two types
• Laharvolcanic ash mobilized by water
• Jokulhlauplarge release of water from a
  sub-glacial lake

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The Armero Tragedy

• Armero, Columbia 1985
• Small eruption from nearby volcano, Nevado del
  Ruiz melted the glacier on top of the volcano
• Water from the glacier mixed with volcanic ash
  creating a lahar
• People can evacuate if they feel like it
• 29,000 people killed
• 80 yrs previous, town buried by mud flows

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Slides

• Slump
• Occurs when blocks of material slide downhill
  over a curved fracture
• Rotated trees
• Jumbled, hummocky front
• Rockslide ( aka rock avalanche
• Bedrock slides downslope over a fracture plane
• Breaks upjumbled chaotic mess of rock
• Fast 500 km/hr

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Rockfall

• Individual blocks plummet in a free fall from a
  cliff or steep mountainside

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Lituya Bay, AlaskaRock Fall Example

• July 9, 1958
• 8.0 earthquake on Fairweather Fault
• Rock fall (slide?) from face of Gilbert Inlet
  slams into Lituya Glacier removing 1,300 ft (1km
  fall)

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• Total volume 30 million m3
• Wave was generated 1720 tall (525m) which
  swashed back and forth due to the Bays shape
• 100 ft (30m) tall when reaches inlet

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• Out of 6 boaters in the bay, 2 killed, 2 tossed
  over the spit into the Pacific, two completely
  unharmed

• 8X greater than any tsunami
• Speed of wave 97-130 mph

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Lituya Bay Images

• Tsunami inundates 13 km2 of woodland
• Sharp line of tree inundation measure of wave
  height
• Wave travels 1.1 km inland

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Landslide Prevention Intro

• Consequences of construction
• Land more susceptible to mass wasting
• Undercuttingremoving support for upper part of
  slope
• Vegetation removal
• Weight of buildings
• Irrigationadding water

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Landslide Prevention 1

• Preventative measures
• Retaining walls with drain pipes
• Terraces
• Planting fast growing grasses and shrubs
• Sloping sheds or tunnels
• Building roads in low landslide risk areas

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Landslide Prevention 2

• Radio-transmitted, real-time monitoring of areas
  that are prone to landslides
• Especially places where roads might be affected
• Bedrock stitching
• Basically drilling holes into bedrock and
  reinforcing with concrete and steel cable
• Education