Geomorphology for Kerala PSC: MASS MOVEMENT

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Kerala PSC

Geomorphology for Kerala PSC: MASS MOVEMENT

  • Mass Movement is transferring the mass of rock debris down the slopes under the direct influence of gravity.
  • The movements of mass may range from slow to rapid, affecting shallow to deep columns of materials and include creep, flow, slide and fall.
  • Gravity exerts force on all matter, both bedrock and the products of weathering. Mass movements are very active over weathered slopes rather than over unweathered materials.
  • Mass movements are aided by gravity and no geomorphic agent like running water, glaciers, wind, waves and currents participate in the process of mass movements.
  • The mass movements do not come under erosion though the materials shifts from one place to another.
  • Materials over the slopes have their own resistance to disturbing forces.
  • Weak unconsolidated materials, thinly bedded rocks, faults, steeply dipping beds, vertical cliffs or steep slopes, abundant precipitation and torrential rains and scarcity of vegetation etc., favour mass movements.
  • The activities that precede mass movements are:
  • removal of support from below to materials above through natural or artificial means
  • increase in gradient and height of slopes
  • overloading through addition of materials naturally or by artificial filling
  • overloading due to heavy rainfall, saturation and lubrication of slope materials
  • removal of material or load from over the original slope surfaces
  • occurrence of earthquakes, explosions or machinery
  • excessive natural seepage
  • heavy drawdown of water from lakes, reservoirs and rivers leading to slow outflow of water from under the slopes or river banks

indiscriminate removal of natural vegetation.

  • The three forms of movements are Heave, flow and slide.

Landslides

  • These are relatively rapid and perceptible movements.  The materials involved in landslides are relatively dry.
  • The size and shape of the detached mass depends on:
  • The nature of discontinuities in the rock
  • The degree of weathering
  • The steepness of the slope.
  • Depending upon the type of movement of materials several types are identified in this category.
  • Slump: It is slipping of one or several units of rock debris with a backward rotation with respect to the slope over which the movement takes place.
  • Debris slide: Rapid rolling or sliding of earth debris without backward rotation of mass is known as debris slide.
  • Debris fall: It is nearly a free fall of earth debris from a vertical or overhanging face.
  • Rockslide: Sliding of individual rock masses down bedding, joint or fault surfaces is rockslide. Over steep slopes, rock sliding is very fast and destructive. Slides occur as planar failures along discontinuities like bedding planes that dip steeply.
  • Rock fall: It is free falling of rock blocks over any steep slope keeping itself away from the slope. Rock falls occur from the superficial layers of the rock face, an occurrence that distinguishes it from rockslide which affects materials up to a substantial depth.

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