GEOLOGICAL HAZARDS (2)

• 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
• Landslide


  A movement of ground, typically down a slope, caused by several factors including slope angle, gravity, and water-induced erosion
• Landslides commonly occur in sloping areas where water flows frequently, loosening the soil and making it susceptible to gravitational pull
• Types of landslide


  • Soil Creep Landslide
  • 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, usually the consequence of removal of buttressing earth at the foot of a slope of unconsolidated material
• 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 depression in the ground that is resulted from the collapse of the surface layer of the soil
• Types of sinkhole


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


  • Sudden collapse of the ground causing catastrophic damage. It develops over an hour
• Cover Subsidence Sinkhole


  • Develop gradually in areas where the covering sediments are permeable and sandy. These sinkholes are small and can go unnoticed for long periods
• Dissolution Sinkhole


  • Occur in areas where limestone is exposed at land surface or is covered by thin layers of soil and permeable sand. Aggressive dissolution also occurs where flow is focused in pre-existing openings in the rock
• Artificial Sinkhole


  • These types of sinkholes can be caused by various human activities, including groundwater pumping and construction activities
• There are different causes of landslide and sinkhole. Any of the triggers are only caused by a triggering element
• Long-term climatic change


  Can significantly impact soil stability. A general reduction in precipitation leads to lowering of water table and reduction in overall weight of soil, reduced solution of material and less powerful freeze-thaw activity
• Earthquakes


  Contribute to landslides worldwide by causing movement of tectonic plates, which also moves the overlying soil. Particularly in areas with steep slopes, earthquakes often result in soil slippage and landslides. Additionally, ashen debris flows triggered by earthquakes can cause significant soil displacement
• Weathering


  It is the natural procedure of rock deterioration that leads to weak, landslide-susceptive materials. It is brought about by the chemical action of water
• EROSION

  Erosion caused by sporadic running water such as streams, rivers, wind, currents, ice and waves wipes out latent and lateral slope support enabling landslides to occur easily.
• • Volcanic eruptionIf an eruption occurs in a wet condition, the soil will start to move downhill instigating a landslide. Stratovolcano is a typical example of volcano responsible for most landslides across the globe. Volcanic gases partially dissolve in groundwater which turns into acidic hydrothermal systems that weakens rock by altering minerals to clay.
• • Forest firesBurns vegetation that holds soil in place.
• • GravitySteeper 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.
• 1. MiningMining 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 cuttingClear cutting 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.
• 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.
• UNDERGROUND WATER PUMPING 

  Pumping water underneath the ground causes drainage to alter their flow which causes the soil to be eroded by water
• DISSOLUTION OF SEDIMENTARY ROCKS 

  When sediment and rocks are dissolveds holes or depression in the ground can be formed