DRRM 4/22

• The Philippines


  • Located in an archipelago
  • Mountainous terrains
  • Often visited by typhoons which bring heavy rain
• The two conditions (mountainous terrains and typhoons) combined in the most unfavorable manner

  May cause landslides and sinkholes which are potential geologic hazards due to the topographic and geologic composition of land
• Landslides and sinkholes


  Soil collapsing downward, but they have different types and characteristics based on composition
• Geological hazards


  • Natural phenomena that cause major problems around the world
  • The expansion and development of cities has led to an increase in impact and damage due to geological hazards
  • Most are related to natural conditions, although some may be due to human activities
• Landslide


  Ground movement on a sloping terrain, does not happen on flat ground
• Landslides


  • 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
  • Structures built on steep-slope mountains have a high vulnerability to landslide hazards especially during heavy rains
  • Areas with steep slope, dense population and denuded terrain are distinguished by a high susceptibility to rainfall-induced landslide hazards
  • Long or regular rain may saturate the topsoil and the bedrock, weakening the soil base of buildings or structures
  • Without plants and trees whose roots can absorb water and hold the soil together, subsequent rain water can continue to loosen up the soil that anchors the buildings
  • A heavy downpour of rain can quickly destroy these buildings and communities, giving way to landslides, mudslides, or mudflows
• Landslide can be considered as a disaster
• Types of Landslides


  • Soil Creep
  • Slumping Landslide
  • Debris Flow Landslide
  • Rock Fall Landslide
• 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 as a unit, usually along a curved plane of failure. The removed mass of soil and rock leave an abrupt drop-off at the top of the landslide known as a scarp.
• 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; the rock on the slope loosens and then slides down the slope.
• Types of Landslides


  • Soil Creep
  • Slumping
  • Debris Flow
  • Rock Fall
• Sinkhole


  A topographic depression created when groundwater dissolves the underlying limestone bedrock, often known as "sink" or "doline"
• Sinkholes


  • 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


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

  2. As water passes through these cracks and fissures, it erodes the soil and forms a conduit system, these underground water systems increase in size as the soil is carried by the water through internal erosion

  3. This can either form a void filled with air with an underground drainage

  4. If the void is clogged with clay, then it forms a depression which then accumulates water and forms a pond

  5. Otherwise, it forms a hole once the cover collapses into the void which can be either filled with air or water
• Sinkholes can be considered as a disaster

  
• Types of Sinkholes


  • Cover Collapse Sinkhole
  • Cover Subsidence Sinkhole
  • Dissolution Sinkhole
  • Artificial Sinkhole

  
• 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


  Such types of sinks may be caused by various human activities, including groundwater pumping and building
• Types of Sinkholes


  • Cover Collapse
  • Cover Subsidence
  • Dissolution
  • Artificial Sinkhole