Understanding Landslide Types, Factors, and Prevention

Posted on Mar 5, 2025 in Geology

Landslides are movements of materials down a slope. They occur on hillsides and slopes due to the force of gravity. The main types of movements are landslides, flows, and avalanches.

Controlling Factors of Landslides

The factors can be internal and external:

  • Internal Factors:
    • Intrinsic:
      1. Lithological: Rock type, degree of consolidation, thickness of mulch and soil.
      2. Structural: Failures, diaclases, bedding planes.
    • Extrinsic:
      1. Environment: Climatic, freeze-thaw cycle, changes in vegetation type, water table changes.
      2. Morphological: Angles of slope steepness.
  • External Factors: Increased water content, vibrations, or human activities (logging, fires).

Slides

Slides are movements of rock or soil on a surface of rupture, where the displaced material is differentiated from the stable material. The displaced ground does not separate at any time from the stable ground. Types of slides include:

  • Planar Slide: If the materials slip on a plane.
  • Rotational Slide: If the materials slip on a curved surface. For example, in the town of Olivares, a rotational slide occurred where 18 hectares of clay moved at a speed of 2 meters per hour, displacing part of the town.
  • Block Slide: Blocks that slip on soft ground (wet clay).

Landslides

Landslides are movements of rock fragments individually. The displaced ground travels for all or part of the time in the air. They may be scarce, in which case they are called falls, or numerous, in which case they are called avalanches. Types of detachments include:

  • Block Falls: The materials follow a path wholly or partly in the air.
  • Detachments by Mismatch: Erosion of lower layers causes vertical cracks, which in turn result in vertical drops of blocks.
  • Toppling Failures: Inconsistent stone materials on layers erode and overturn the superior materials.
  • Subsidence and Collapse: Subsidence phenomena are slow movements of terrain due to compaction of the territory or extraction of fluids from inner layers. Collapses are the sudden collapse of a limestone cave due to dissolution or karstification.

Flows

Flows are displacements of unconsolidated material with high water content, which behaves like a viscous fluid:

  • Creep: The gradual decline of the mantle of alteration, which affects only the uppermost layer of the slopes and altered clay, affecting a large area.
  • Mudflows or Solifluction: Formed by soft and loose materials from water-soaked clays: clay flows, valley flows, torrential bursts, and drag. When puffs occur in periods of hydration (rain) and contractions and cracking during periods of dryness, they are called expansive soils.

Prediction and Prevention of Landslides

Preventive Measures:

  • Spatial Prediction: Risk mapping.
  • Temporal Prediction: Studies of precursors that allow detection of instabilities: forms of erosion and deposit, deformation in vegetation, poles, or fences. Instruments that can be used include crack expansion meters, geophones for vibrations, photoelectric cells in anchorage, etc.

Corrective Measures:

  • Land use systems to prevent occupation of risk areas and activities that induce increased risk.
  • Drainage by ditches, pits, or trenches to reduce runoff and waterlogging.
  • Slope modifications to increase the resistance of the terrain: injection of cohesive materials, steel bars.
  • Retaining structures: Containment walls or buttresses, netting.
  • Guidance of small falls.
  • Reforestation with herbaceous plants or fast-growing trees on hillsides.