Chapter 8
Subsidence and Collpase
  • Downward settling or sinking of earth surface
  •  Destructive, BUT very slowly like landslide
  •  YET costs US some 10s of millions of $/ year

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    Causes of Subsidence

    1.  Natural
    2.  Human induced
    Natural: Earthquakes, volcanic Activities, Dissolution of CaCO3, dolomites, salts

     Earthquakes cause subsidence by

    1. Displacement along faults e.g. in Alaska (up to 1m)
    2.  Ground shaking to cause liquifaction of soil e.g., MISSISSIPPI R. Valley
    Volcanic Activities cause subsidence by emptying magma chambers

    (Figure here)

    Dissolution of CaCO3 results in Caves and Caverns that may collapse to depressions => SINK HOLES

    (Figure here)

    Human Induced Subsidence

  •  From disturbance of environment by humans
    1.  Groundwater pumping
    2.  Extraction of oil and gas
  • Costly/Expensive
  •  Cost US 10s of millions $/year
  •  Change drainage patterns previously in place to protect people, plants, animals

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    Classification of Subsidence

  •  According to depth of initiation
    1.  DEEP SUBSIDENCE: at considerable depth
    2. SHALLOW SUBSIDENCE: close to ground surface
    Shallow subsidence could be:
    1. Collapsing Soil OR Hydro-compaction:
      2. (Figure here)
    2. Sinkhole Collapse:
      3. (Figure here)

      (Figure here)

    3.  Shallow Mines:
    e.g. of Major Subsidence/Collapse Events
    1. Many homes in Florida suddenly disappeared
    2. Failure of Balduir (??) Hill Dam
    3. Subsidence in Mexico City
    MITIGATION
  • Difficult because possible areas cannot all be predicted in advance
  •  We learn mover about collapse/subsidence from occurrences
  •  BEST STRATEGY:
    • *Control water table levels READ UP

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