DRRR

• A landslide is the very slow to rapid downward movement of a big bulk of soil, debris, rock, and garbage down a slope
• A landslide happens if the driving force (the force that cause the slope to move) is greater than the resisting force (the force that stabilize the slope and prevent movement)
• Landslides are openings or pits in the ground surface caused by the collapse in the ceiling of an underground cavity or space
• A sinkhole is formed due to the absence of external surface drainage when water gathers inside; the water would just drain into the subsurface
• Sinkholes naturally occur in areas underlain by minerals and rocks that are soluble or can be dissolved by water
• Geological hazards


  • Discuss the different geological hazards

  2. Analyze the causes of geological hazards

  3. Recognize signs of impending geological hazards
• Landslide


  Very slow to rapid downward movement of a big bulk of soil, debris, rock, and garbage down a slope
• Driving force


  The force that cause the slope to move
• Resisting force


  The force that stabilize the slope and prevent movement
• There would be no landslide if the resisting force (e.g. strength of the material, lateral confining forces due to a retaining wall) is greater than or equal to the driving force (e.g. gravity, seepage, earthquake forces)
• Reasons why driving force dominates

  • Steepness of the slope

  Weakness or weathering of geological materials

  Deforestation

  Too much loading on the slope

  Water leakage from utilities
• Triggers of landslides


  • Extreme rainfall which saturates the slope with water

  Vibrations caused by earthquakes

  Human activities
• Types of materials in landslides

  • Rock

  Earth

  Soil

  Mud

  Debris
• Types of movement in landslides

  • Fall

  Topple

  Slide

  Spread

  Flow
• Sinkhole


  Openings or pits in the ground surface caused by the collapse in the ceiling of an underground cavity or space
• Sinkhole


  Depression or hole in the ground that forms when the surface layer of soil or rock collapses, often due to the erosion of underground water or the dissolution of soluble rocks like limestone or gypsum
• Causes of sinkholes


  • Natural processes: Dissolution of soluble rocks like limestone or gypsum due to groundwater movement

  Human activities: Mining, drilling, construction

  Heavy rain or flooding

  Drought

  Changes in groundwater levels
• Types of sinkholes

  • Dissolution sinkholes

  Cover subsidence sinkholes

  Cover-collapse sinkholes
• Dissolution sinkhole


  Occurs in areas with little soil or vegetation over soluble rock, where aggressive dissolution occurs in pre-existing openings in the rock, and they typically develop gradually
• Cover-subsidence sinkhole


  Develops gradually where the covering sediments are permeable and contain sand