GEOLOGICAL HAZARDS

• The expansion and development of cities has led to an increase in impact and damage due to geological hazards
• Most of the geological hazards are related to natural conditions, although some may be due to human activities
• Types of geological hazard

  • Landslide
  • Sinkhole
• Landslide


  • A ground movement on a sloping terrain. It does not happen on flat ground because of the angle on the ground, gravity induces the land to move downward. It is aggravated by rain because water is a natural agent for erosion. If rain or any source of water frequently flows down a sloping area, the gravitational descent of loosened soil makes it possible for landslide to occur
• Types of landslide


  • Slumping landslide
  • Debris flow landslide
  • Rock fall landslide
  • Soil creep landslide
• Debris flow landslide


  • Happens when the slope becomes saturated with water, this then triggers a landslide of water-soaked mass of rock and soil that slides down the slope
• Rock fall landslide


  • Sudden slides caused by heavy rain that loosens the rock on the slope and then slides down the slope
• Sinkhole


  A topographic depression created when groundwater dissolves the underlying limestone bedrock. Often known as "sink" or "doline"
• Sinkhole


  • Occur in areas where the soil foundation is made of soft minerals and rocks such as limestone, salt beds, or any acidic rocks. The depth of sinkholes ranges from a couple of meters to several mile deep
• How sinkholes occur


  Water seeps underground through cracks and fissures, eroding soil and creating conduit systems. This can lead to the formation of voids which can either be filled with air or water, depressions that accumulate water and form ponds, or holes filled with air or water once the ground collapses into the void
• Cover subsidence sinkhole


  • It gradually grows where the sediment covers are permeable and contain sand
• Dissolution sinkhole


  • It occurs in areas where calcareous is exposed on the ground or where thin layers of soil and permeable sand are also covered. Limestone or dolomite dissolution is most intense when the water first reaches the rock surface
• Artificial sinkhole


  • Such types of sinks may be caused by various human activities, including groundwater pumping and building
• Natural causes of landslides

  • Climate
  • Earthquake
  • Weathering
• Weathering


  It is the natural procedure of rock deterioration that leads to weak, landslide susceptible materials. It is brought about by the chemical action of water, air, plants and bacteria. When the rocks are weak enough, they slip away causing landslides
• Human causes of landslides

  • Mining
  • Clear cutting
• Cable and reduction in overall weight of soil mass


  • Reduced solution of materials and less powerful freefall activity
  • A significant upsurge in precipitation or ground saturation would dramatically increase the level of ground water
  • When slowed areas are completely saturated with water, landslides can occur
  • If there is absence of mechanical root support, the soils start to run off
• Weathering


  • The natural procedure of rock deterioration that leads to weak, landslide susceptible materials
  • It is brought about by the chemical action of water, air, plants and bacteria
  • When the rocks are weak enough, they slip away causing landslides
• Gravity


  • Steeper slopes coupled with gravitational force can trigger a massive landslide
  • Steeper slopes can also cause the debris to move farther from the foot of the area
• Human cause of landslide

  • Mining
  • Clear cutting
• Mining


  • Activities that utilize blasting techniques contribute mightily to landslides
  • Vibrations emanating from the blasts can weaken soils in other areas susceptible to landslides
  • The weakening of soil means a landslide can occur anytime
  • Earthwork alters the shape of a slope, imposing new loads on an existing slope
• Clear cutting


  • It is a technique of timber harvesting that eliminates all old trees from the area
  • This technique is dangerous since it decimates the existing mechanical root structure of the area
  • It changes the amount of water infiltrating the soil
• Dissolution of sedimentary rocks

  • Sinkholes occur when sedimentary rocks are dissolved
  • When these rocks are dissolved, it can either form a void of water or air
  • A void filled with air forms a hole and a void filled with underground water makes a lake or a pond
  • Sinkholes can be in the form of holes or depressions on the ground