Drrr

• 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 of the geological hazards are related to natural conditions, although some may be due to human activities
• Landslides


  Ground movement on a sloping terrain
• Sinkholes


  Topographic depression created when groundwater dissolves the underlying limestone bedrock
• As a student you need to be aware of the different types of landslides and sinkholes in order to be prepared for the danger that it may cause
• Landslide


  1. Gravity induces the land to move downward

  2. Water is a natural agent for erosion

  3. 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

  • High vulnerability to landslide hazards especially during heavy rains
• Areas with


  • Steep slope
  • Dense population
  • Denuded terrain
• 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
• Types of Landslide


  • Soil Creep Landslide
  • Slumping Landslide
  • Debris Flow Landslide
  • Rock Fall landslides
• 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


  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 landslides


  Sudden slides caused by heavy rain 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
  • 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

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

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

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

  6. Otherwise it forms a hole once the cover collapses into the void which can be either filled with air or water
• 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
• Causes of Landslide


  • Natural causes: Climate
  • Earthquakes
  • Weathering
  • Flooding
  • Volcanic Activity
  • Forest Fires
  • Gravity

  Human causes: 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
• Rainfall can be a cause for landslides, but soil conditions are also very critical
• The features of precipitation occurrences, including the accumulated volume of rainfall, length and severity, and the slope of the terrain show the greatest effect on the stability of the slope and the rate of occurrence of landslides and debris
• The precipitation-induced landslide depends on the type of land covered and the type of soil
• Soil Creep Landslide


  The level of creep induced by one rainfall has a strong association with the amount of rainfall and changes in soil moisture
• Debris Flow Landslide


  Colluvial landslide in a debris flow valley is a common occurrence that is quickly caused by rainfall. The direct destructiveness of this type of landslide is limited, but if failure occurs, the resultant blockage of the channel can lead to a series of magnified secondary hazards
• Natural Causes of Sinkhole

  • Dissolution of sedimentary rocks
• Human Causes of Sinkhole

  • Underground water pumping
  • Broken pipes underneath the ground
• Cover Collapse Sinkhole


  Develop abruptly (over a period of hours) and thus cause catastrophic damages. They occur where the covering sediments contain a significant amount of clay
• Cover Subsidence Sinkhole


  Develop gradually where the covering sediments are permeable and contain sand
• Dissolution Sinkhole


  Occur in areas where limestone is exposed at land surface or also is covered by thin layers of soil and permeable sand. Dissolution of the limestone or dolomite is most intensive where the water first contacts the rock surface
• Sinkholes


  • Can be caused by internal erosion making a void underneath the ground
  • Can be caused by altering drainage systems causing water to branch into other routes where there is soluble rock
• Types of sinkholes


  • Cover collapse sinkhole
  • Cover subsidence sinkhole
  • Dissolution sinkhole
  • Artificial sinkhole
• Cover collapse sinkhole


  • Develop abruptly (over a period of hours) and thus cause catastrophic damages
  • Occur where the covering sediments contain a significant amount of clay
  • Over time, surface drainage, erosion, and deposition of sinkhole into a shallower bowl-shaped depression