Geological Disaster (Sinkhole & Landslide)

• Sinkhole


  A hole in the ground that forms when water dissolves surface rock
• Limestone


  • Usual type of surface rock
• Natural causes of sinkhole

  1. Dissolution of sedimentary rocks

  2. Sinkholes occur when sedimentary rocks are dissolved

  3. Dissolution can form a void of water or air
• Human causes of a sinkhole

  1. Underground water pumping

  2. Water flow alteration

  3. Erosion of the rock beneath
• Types of sinkholes

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

  • Develops abruptly (usually an hour)
  • Occur where the covering sediments contain a significant amount of clay
• Cover subsidence sinkhole


  • Develops slowly over time
  • Covering sediments are permeable and contains sand
• Dissolution sinkhole


  • Occurs in areas where the limestone was exposed directly or covered by some sediments
  • Dissolution of the surface is extensive when in direct contact with water
• Artificial sinkhole


  • Sinkholes caused by various human activities
• Signs of an impending sinkhole

  • Trees or fence posts that tilt or fall
  • Foundations that slant
  • New small ponds that appear after rain
  • Cracks in a flat ground
  • Sudden drainage of a pond
  • Dead patches of grass or plants
  • Well water that is discolored or contaminated with debris
  • Cracking or buckling of home's concrete slab
  • Presence of odd bugs like slugs, centipedes in homes
• Geological Hazards (Landslides)

  Ground movement on a sloping terrain, gravity induces the ground to move downward, aggravated by erosion
• Landslide


  Ground movement on a sloping terrain
• Soil Creep Landslide


  • Very slow (hence the term "creep") downslope movement, happens with every slope with loose, weathered soil
• Slumping Landslide


  • Characterized by a concave slump/curved plane of failure
• Debris Flow Landslides


  • Happens when the slope was saturated with water, also known as mudslides
• Rock Flow Landslides


  • When rocks slid down the slope, usually caused by heavy rain
• What are the Natural Causes of Landslides

  • Rainfall
  • Earthquakes
  • Volcanic Eruption
  • Forest Fires
  • Gravity
• Human Causes of Landslides

  • Mining
  • Clear-Cutting
• List 4 Signs of Impending Landslides

  • Earlier Landslide
  • Tension Cracks
  • Things Moving
  • Water Doing Something Different
• • Earlier Landslide: Be careful if there are slow and weak ground movement, it means the soil was loose, this could cause a second but a more massive landslide
• • Tension Cracks: Caused by stress and friction produced by movement of geologic materials, cracks found on high ground are landslide indicators
• • Things Moving- Deformation of the terrain is a red flag, obvious sign of slow ground movement are trees bended into a J-curve
• • Water Doing Something Different- Changes in water flow, if springs or wet ground can be found on a terrain that is supposed to be dry
• Soluble Rocks: Limestone, Gypsum, Salt, Carbonate Rock Formation
• Debris Flow Landslide Known as "mudslides"
• Rock Flow Landslides Known as "most dangerous landslide" caused by heavy rain
• Soil ripples


  It is the small waves or ridges on the surface.

  
• Depression


  What does cover subsidence sinkhole forms?

  
• Structural arch 


  What does cover collapse sinkhole forms?

  
• If water is altered = erosion of rock