Q4

• Geological hazards - gradual or sudden natural earth processes which cause injury, loss of life, property damage, loss of livelihood and services, social and economic disruption, or environmental changes.
• Some examples of Geological hazards are:

  • earthquakes
  • landslides
  • volcanic eruption
  • sinkholes
• • Landslide - A mass of rock, soil, or other debris that moves downhill
• Landslides - the movement of a mass of rock, debris, or earth down a slope.
• Major Causes of Landslides

  1. Geology
  2. Topography
  3. Morphology
  4. Human activities
• Geology – this refers to the material of the soil or rock in the area or can be the layers of earth has weakened or stiffened in some part.
• Morphology – this refers to the structure of the land. The soil or rock has weakened through loss of vegetation or root system which holds the soil in place. Another is prolonged rainfall or heavy water leakage that increases the weight of the land mass therefore as the water flows, sediments and soils also comes 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.
• The most common landslide we have experienced here in the Philippines is the rainfall-induced landslide.
• Rainfall-induced Landslide:

  occurs due to prolonged or heavy rainfall, increasing the weight of the land mass. The development of a rainfall-induced landslide may take several days but the landslide itself will only take a few minutes to cause a disaster. Rainfall-induced landslides can form debris flows when they mix with additional water and sediments from their path. It may sweep away a whole community in an instant
• impending signs of a 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)
• Early Warning System (EWS) of the Philippine Institute of Volcanology and Seismology (PHILVOCS) and Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) are monitoring systems designed to forecast events accompanying landslides in order to provide a warning about hazards
• Types of Landslide:

  1. Soil Creep Landslide
  2. Slumping Landslide
  3. Debris Flow Landslide
  4. Rock Fall landslides
• 1. Soil Creep Landslide - is a very slow downslope movement of particles that occurs in every slope covered with loose, weathered material (Britannica dictionary).
• 2. Slumping Landslide - is a downward movement of rock debris, usually the consequence of removal of buttressing earth at the foot of a slope of unconsolidated material (Britannica dictionary).
• 3. 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.
• 4. Rock Fall landslides - are sudden slides caused by heavy rain the rock on the slope loosens and then slides down the slope.
• 1. Soil Creep Landslide - is a very slow downslope movement of particles that occurs in every slope covered with loose, weathered material (Britannica dictionary).

  
• 2. Slumping Landslide - a downward movement of rock debris, usually the consequence of removal of buttressing earth at the foot of a slope of unconsolidated material (Britannica dictionary)

  
• 3. 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.

  
• 4. Rock Fall landslides - sudden slides caused by heavy rain the rock on the slope loosens and then slides down the slope.

  
• Sinkhole - a topographic depression created when groundwater dissolves the underlying limestone bedrock. Often known as "sink" or "doline,".
• Sinkhole - is a depression or hole in the ground caused by some form of collapse of the surface layer.
• Characteristics of a sinkhole:

  • 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.
• Sinkholes has two kinds -> natural or man-made
• Natural sinkholes - are caused by physical or chemical erosion. The natural flow of water may erode rock material while acidic substances may also dissolve and eventually weaken it.
• Man-made sinkholes - are 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.
• How sinkholes occur


  1. Water from rainfall seeps underneath soil through cracks and fissures

  2. Water erodes soil and forms conduit system

  3. Underground water systems increase in size as soil is carried by water through internal erosion

  4. Void filled with air with underground drainage

  5. Void clogged with clay forms depression which accumulates water and forms pond

  6. Void not clogged forms hole once cover collapses into void, filled with air or water
• Types of sinkholes:

  1. Solution sinkholes
  2. Cover Subsidence Sinkholes
  3. Cover Collapse Sinkholes
  4. Dissolution Sinkhole
  5. Artificial Sinkhole
• Solution Sinkhole - are common in areas that have thin cover of soil on the surface of the ground which exposes the bedrock to water erosion. As the bedrock erodes, particles collect in the spaces it leaves and a small depression is formed over a period, eventually forming a hole. The bedrock may collapse suddenly, or it may happen over time.
• Cover Subsidence Sinkholes - this occur when the bedrock is covered by soil and materials that are not well-knitted together. The soil in these areas are made mostly of clay or sand. Once the bedrock starts to erode, the clay or sand starts to enter through the cracks and settles into the spaces left behind, creating a cavity on the surface of the soil.
• Cover Subsidence Sinkhole - It gradually grows where the sediment covers are permeable and contain sand.
• Cover Collapse Sinkholes – occur when the bedrock is covered by a deep layer of soil and earth. A crack starts once the bedrock begins to get eroded. Weak points begin to form in the layers of soil above it. The weak points eventually become a large hole within the bedrock that cannot support the weight above it. The collapse occurs in an instant and can create large holes in a matter of minutes.
• Cover Collapse Sinkhole - It develops suddenly (over an hour period) thus, causing catastrophic damage.
• Dissolution Sinkhole - It takes years to decades to form.
• Dissolution Sinkhole - It 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.
• Dissolution Sinkhole - Over time, the chemical reaction causes small cavities to form in the limestone. These cavities enlarge as more water enters them, eventually leading to the formation of a sinkhole.
• Artificial Sinkhole - Such types of sinks may be caused by various human activities, including groundwater pumping and building.
• The impending signs of a sinkhole:

  • New cracks at the foundations of buildings and houses
  • Cracks in an area
  • Depressions at ground level
  • Rapid appearance of a crater in the ground
• Geological hazard maps - map showing the areas that are vulnerable to earthquake threats, volcanic eruptions, and landslides. It is a tool that scientists and local authorities use to anticipate any hazard that a geological event could bring.