OAS Mains Q&A: Landslides and Mass Movements

Subject: General Studies

Paper-I

Geography of India & Environment and Ecological Issues

Question

What are the different causes of Landslides? Suggest different measures to mitigate the menace of landslides and mass movements.

Sample Answer

Landslides are a regular natural hazard experienced in the hilly and mountainous areas all over the world. These are a type of “mass wasting,” which denotes any down-slope movement of soil and rock under the direct influence of gravity. The term “landslide” encompasses five modes of slope movement: falls, topples, slides, spreads, and flows. These are further subdivided by the type of geologic material (bedrock, debris, or earth). Debris flows (commonly referred to as mudflows or mudslides) and rock falls are examples of common landslide types.

Natural Causes of landslides

Landslides are caused due to several factors. Some may be natural, and some may be human induced. The natural causes of landslides include:

  • Change in Hydrologic conditions: The groundwater (pore water) pressure may be acting to destabilize the slope. Heavy rainfall adds to the slope destability.
  • Change in Vegetation: Loss or absence of vertical vegetative structure, soil nutrients, and soil structure due to forest fires or mining.
  • Removal of Surface Mass: The erosion of the toe of a slope by running river water or rainwater
  • Snowmelt: Weakening of a slope through saturation by snow melt, glaciers melting, or due to heavy rains.
  • Seismically Induced Changes: The occurrence of micro-seismic waves or tremors. This may also include earthquake-induced liquefaction which may be destabilizing the slopes.
  • Volcanic eruptions– may also cause landslides.

Human activities responsible for landslides are –

  • Deforestation & Cultivation,
  • Disturbance of the drainage patterns through cut and fill operations
  • Construction, Blasting, Mining and Quarrying
  • Vibrations from machinery or heavy traffic and movement of heavy vehicles
  • Earthwork which alters the shape of a slope and imposes new loads on the existing slopes
  • Removal of deep-rooted vegetation
  • Bushfires for clearing trees

Mitigation Measures

  • The study of landslides helps in identifying the weak zones, classifying the hill slopes in to different categories and to minimize the impacts of landslides. In this Landslide zonation becomes vital step.
  • Control the surface and sub surface drainage systems. Subsurface drainage is carried out by installing horizontal drains, vertical wells, deep trench drains, drainage galleries and drainage tunnels and weep holes. These drains are meant to remove excess subsurface water and reduce the saturation within hillside slopes.
  • It is necessary to prevent sliding or, in the case of an existing failure, to prevent a reactivation of the movement. This could be done by increased vegetation and afforestation.
  • The other common corrective measures include levelling, proper grading and drainage, and construction of retaining walls.
  • More sophisticated remedies include anchors, bolts, and dowels.

Impacts of landslides

  • Occurrence of landslides also change the general landscape or the geomorphic conditions.
  • The topography and drainage get modified due to these hazards. Landslides can destroy the forests and other resources.
  • Landslides will also damage the man-made structures like roads, railways, tunnels and buildings on the hilly regions.

Increasing human interference with nature has led to rise in the number of natural disasters. Although National Disaster Response Force under The Disaster Management Act, 2005 has conducted several successful rescue operations by providing aid and assistance to the affected state, including deploying, at the State’s request, of Armed Forces, Central Paramilitary Forces, and such communication, air and other assets, but there is a need of comprehensive efforts of all stakeholders to minimize the impact of landslides.

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