Geological Hazards

• Geological hazards


  Adverse geologic conditions capable of causing widespread damage or loss of property and life
• Geological hazards


  • Arise from both long-term and short-term geological processes
• Landslide


  Ground movement on a sloping terrain
• Landslides do not happen on flat ground because of the angle on the ground, gravity induces the land to move downward
• Landslides are 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
• Soil Creep Landslide


  Very slow downslope movement of particles that occurs in every slope covered with loose, weathered material
• Slumping Landslide


  Downward movement of rock debris, usually the consequence of removal of buttressing earth at the foot of a slope of unconsolidated material
• Debris Flow Landslide


  Landslide of water-soaked mass of rock and soil that slides down the slope when the slope becomes saturated with water
• Rock Fall Landslide


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


  Topographic depression created when groundwater dissolves the underlying limestone bedrock
• Sinkholes


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


  1. Water from rainfall seeps underneath the soil through cracks and fissures

  2. Water erodes the soil and forms a conduit system

  3. Underground water systems increase in size as the soil is carried by the water through internal erosion

  4. Can form a void filled with air with an underground drainage
• Cover Collapse Sinkhole


  Develops suddenly (over an hour period) thus, causing catastrophic damage
• Cover Subsidence Sinkhole


  Gradually grows where the sediment covers are permeable and contain sand
• Dissolution Sinkhole


  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


  May be caused by various human activities, including groundwater pumping and building
• Causes of landslides


  • Climate
  • Earthquakes
  • Weathering
  • Erosion
  • Volcanic eruption
  • Forest fires
  • Gravity
• Human causes of landslides


  • Mining
  • Clear cutting
• Rainfall-induced landslides are the most common and widespread damaging landslides in the Philippines, with an average of 20 typhoons each year due to prolonged or heavy rainfall
• Most rainfall induced landslides are shallow (less than a few meters deep), thin, and move quickly
• Dissolution of sedimentary rocks

  Sinkholes occur when sedimentary rocks are dissolved, forming a void of water or air
• Underground water pumping


  Pumping water underneath the ground causes drainage to alter their flow which causes the soil to be eroded by water
• Broken pipes underneath the ground can also cause internal erosion making a void underneath the ground
• Altering drainage systems cause water to branch into other routes where there is soluble rock can cause erosion through the flow of water