DRRR_1

• Geological hazards


  Gradual or sudden natural earth processes that cause injury, loss of life, property damage, loss of livelihood and services, social and economic disruption, or environmental damages
• Landslide


  Rock, dirt, or debris falling down a sloping section of land
• Three major causes of landslides


  • Geology
  • Morphology
  • Human activity
• Natural causes of landslides


  • Climate
  • Earthquakes
  • Weathering
  • Erosion
  • Volcanic eruption
  • Forest fires
  • Gravity
• Geology


  • Material of the soil and rock in the area
  • Layers of the earth have weakened or stiffened in some parts
• Morphology


  • Structure of the land
  • Soil or rock has weakened through the loss of vegetation or root system which holds the soil in place
  • Prolonged rainfall or heavy water leakage increases the weight of the land mass therefore, as the water flows, sediments and soils come with it
• Human activity


  • To make way for agriculture and construction, trees are needed to be cut down
  • Irrigation, deforestation, and excavation can weaken the integrity of the earth
• Climate


  • Long-term climatic changes can significantly impact soil stability
  • Reduction in precipitation leads to lowering of the water table and reduction in overall weight of soil mass, reduced solution of materials, and less powerful freeze-thaw activity
  • Significant upsurge in precipitation or ground saturation would dramatically increase the level of groundwater
  • When completely saturated with water, landslides can occur
  • If mechanical root support is absent, the soil starts to run off
• Earthquakes


  • Any moment tectonic plates move, the soil covering them also move along
  • When earthquakes strike areas with steep slopes, on numerous occasions, the soil slips leading to landslides
  • Ash and debris flows instigated by earthquakes could also cause mass soil movement
• Weathering


  • Natural procedure of rock deterioration that leads to weak-landslide susceptive materials
  • It is brought about by the chemical action of water, air, plants, and bacteria
  • When the rocks are weak enough, they slip away causing landslides
• 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 eruption


  • If 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 fires

  • Burns vegetation that holds soil in place
  • The risk of landslides prevails for up to 20 years in dry climates
  • Wildfires removes the protective ability of vegetation which increases runoff, erosion, and debris flow because the water cannot penetrate through the soil thus carrying the debris downslope
  • Burrowing insects also play a role by aerating the soil destabilizing it during a wildfire because they tend to seek for cooler soil to survive
• Gravity


  Steeper 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
• Mining


  • Mining 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 at anytime. Earthwork alters the shape of a slope, imposing new loads on an existing slope
• Clear-cutting

  • A technique of timber harvesting that eliminates all odd trees from the area
  • This is a dangerous since it decimates the existing mechanical root structure of the area. It changes the amount of water inflitrating the soil
• Rainfall-induced landslide


  • Occurs due to prolonged or heavy rainfall, increasing the weight of the land mass
  • It may take several days but the landslide itself will only take a few minutes to cause a disaster
  • Can form debris flows when they mix with additional water and sediments from their path and may sweep whole community in an instant
• Impending signs of rainfall-induced landslide


  • Unusual noises, such as breaking trees, or knocking boulders together, can mean moving debris
  • As the landslide nears, a slight rumbling sound that rises in amplitude is noticeable
  • Rapid rise in water levels of the creeks, likely followed by increased turbidity (soil content)
• Soil creep landslide


  • Is a very slow downslope movement of particles that occurs in every slope covered with loose, weathered material
  • The level of creep induced by one rainfall has a strong association with the amount of rainfall and changes in soil moisture
  • For the valley-head slope, the dirt creeps down and accumulates a hollow portion of the head at the bottom of the bottleneck, under which the dirt is compressed and forms a wave-shaped soil
• Slumping landslide


  A downward movement of rock debris, usually the consequence of removal of buttressing earth at the foot of a slope of unconsolidates 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
  • 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
  • For this cause, it is important to explore the possible response of this type of landslide to rainfall
• Rock fall landslides


  Sudden slides caused by heavy rain in the rock on the slope loosens and then slides down the slope
• Sinkhole


  • A depression or hole is caused by the collapse of the surface layer of the ground
  • Water is the primary cause of most sinkholes when it dissolves soluble rocks such as limestone, dolomite, and gypsum
• Two kinds of sinkholes


  • Natural sinkholes
  • Man-made sinkholes
• Natural sinkholes


  • Caused by physical or chemical erosion
  • Water may erode rock minerals while acidic substances may also dissolve and eventually weaken it
• Man-made sinkholes


  • Caused by drilling, mining, road construction and broken water or underground pipes
  • Water may penetrate through mud and rocks and eventually erode the ground underneath
• Types of sinkholes

  • Solution sinkholes
  • Cover subsidence sinkholes
  • Cover collapse sinkholes
  • Artificial sinkhole
• Solution sinkholes

  • 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
  • Aggressive dissolution also occurs where flow is focused in joints, fractures, and bedding planes, and in the zone of water-table fluctuation where groundwater is in contact with the atmosphere
  • Solution sinkholes are generally small in size and also slow to develop
• Cover subsidence sinkholes

  Develop gradually where the covering sediments are permeable and contain sand. In areas where cover material is thicker or sediments contain more clay, cover-subsidence sinkholes are relatively uncommon and therefore may not be seen frequently. They are smaller and thus may go undetected for long periods
• Cover collapse sinkholes


  Develop abruptly (over hours) and thus cause catastrophic damages. They 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
• Artificial sinkhole


  Caused by various human activities, including groundwater pumping and construction activities. However, the most common activities that result in artificial sinkholes are mining, drilling, considerable changes in weight, as well as a tremendous increase in water flow, such as a construction of an artificial pond
• Impending signs of a sinkhole


  • New cracks at the foundations of buildings and houses
  • Crack in an area
  • Depressions at ground level
  • Rapid appearance of crater in the ground