Geological Hazards

• Geological hazard - is geological process or phenomenon that may cause loss of a life, injury or other health impacts,

  property damage, loss of livelihoods and services, social and economic disruption, or environmental damage.
• Geological hazards - are responsible for great loss of life and destruction of property.
• Landslide - is a geological phenomenon which includes a wide range of ground movement, such as rock falls, deep failure

  of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments.
• A landslide, also called "landslip", is a ground movement on a sloping

  terrain. Landslides do not happen on flat grounds.
• Natural Causes of Landslides

  • Earthquakes

  Seismic activities have always been a main cause of landslides throughout the world. When earthquakes occur on areas

  with steep slopes, oftentimes the soil slips causing landslides. Furthermore, ash and debris flows caused by earthquakes

  may also trigger mass movement of soil.

  • Heavy Rainfall

  When sloped areas become completely saturated by heavy rainfall, landslides may occur, Without the aid of mechanical

  root support the soil simply runs off when it contains too much water.
• Human Causes of Landslides

  • Clear Cutting

  This method is hazardous because it destroys the existing mechanical root structure in the area.

  • Mining

  Mining operations that use blasting techniques often cause other areas that are at the risk of sliding to slide due to

  vibrations under the soil.
• Slope movement - occurs when forces acting down-slope (mainly due to

  gravity) exceed the strength of the earth materials that compose the slope.
• Earthquake shaking and other factors can also induce landslides underwater. These landslides are called submarine

  landslides.
• Submarine landslides - sometimes cause tsunamis that damage coastal areas.
• Sinkholes - are depressions or holes on the ground that resulted from the collapse of the surface layer of the soil.
• In areas that are susceptible to landslides, an Abney level or a laser rangefinder equipped with a tiltmeter

  is used to measure the slope angle, soil compaction, and soil strength of an area.
• Sinkholes are validated using ground-penetrating radar to provide images of subsurface ground.
• Water - natural agent for erosion, and if rain or any source of water

  frequently flows down a sloping area, the gravitational descent of

  loosened soil makes it possible for landslides to occur.
• water, wind, and ice - 3 forces of erosion
• A high vulnerability to rainfall-induced landslide hazards is

  characterized by areas with steep slope, dense population, and

  denuded ground.
• Landslides can be triggered by rainfall,

  snowmelt, changes in water level, stream erosion, and changes in ground water, earthquakes, volcanic activity,

  disturbance by human activities, or any combination of these factors.
• Landslides can move slowly, (millimeters per year) or can move quickly and disastrously, as is the case with debris flows.

  Debris flows can travel down a hillside at speeds up to 200 miles per hour (more commonly, 30 - 50 miles per hour),

  depending on the slope angle, water content, volume of debris, and type of earth and debris in the flow.
• Sinkholes

  occur in areas where the soil foundation is made of soft minerals and rocks such as limestone, salt beds, or any acidic

  rocks.
• Natural sinkholes occur due to erosion of underground water.
• Geological hazards


  Hazards caused by geological processes
• Good penetration is achieved in

  soft layers or porous materials such as dry sandy soils or massive dry materials such as limestone. The measurement can

  reach up to 15 meters. This is why the GPR is a good tool in determining whether sinkholes may occur or not because of

  the relatively accurate determination of the soft ground underlying the ground surface. The GPR has been widely used in

  mapping sinkholes in Bohol and Cebu, where both showed the presence of sinkholes during an earthquake event in 2013.
• Areas that have the highest vulnerability to rainfall-induced landslides have already been identified by the MGB of the

  Department of Environment and Natural Resources (DENR) through their Geohazard Mapping and Assessment Program.

  This program is an ongoing priority project of the DENR designed to provide accurate and detailed profile of the terrain

  of the Philippine soils. The maps generated from this project have combined landslides and flooding hazards as these two

  are the most common geologic issues in sloping areas during rainfall.
• Top 10 Most Landslide Prone Provinces of the Philippines

  1. Marinduque
  2. Rizal
  3. Cebu
  4. La Union
  5. Southern Leyte
  6. Benguet
  7. Nueva Viscaya
  8. Batangas
  9. Mountain Province
  10. Romblon
• Causes of Geological Hazards

  According to Kusky (2003), there are several causes of geological hazards namely;

  1. The slow but steady movement of tectonic plates on the surface of the earth causes many geologic hazards either

  directly or indirectly. Plate tectonics control the distribution of earthquakes, the location of volcanoes, and the uplifting of

  mountain ranges;
• 2. Earth surface processes, including river flooding, coastal erosion, and changing climate zones are parts of natural earth

  cycles but are considered hazardous to humans because we have not adequately understood the cycles before building on

  exposed coastlines and in areas prone to shifting climate zones; and
• 3. The kind of materials, such as clay that dramatically expands when wetted and sinkholes that develops within

  limestone.
• Mitigation Strategies to Prevent Loss of Lives and Properties

  1. Restricting Development in Landslide-Prone Areas. Land use planning is one of the most effective and economical

  ways to reduce landslide losses by avoiding the hazard and minimizing the risk. This is accomplished by removing or

  converting existing development or discouraging or regulating new development in unstable areas.
• 2. Codes for Excavation, Construction, and Grading Codes. Excavation, construction, and grading codes have been

  developed for construction in landslide-prone areas. There is no nationwide uniform code to ensure standardization

  instead, State and local government agencies apply design and construction criteria that fit their specific needs.
• 3. Protecting Existing Development. Stability of a slope can be increased by removing all or part of a landslide mass, or

  by adding earth buttresses placed at the toes of potential slope failures. Restraining walls, piles, caissons, or rock anchors,

  are commonly used to prevent or control slope movement. In most cases, combinations of these measures are used.
• 4. Monitoring and Warning Systems. Monitoring and warning systems are utilized to protect lives and property, not to

  prevent landslides. However, these systems often provide warning of slope movement in time to allow the construction of

  physical measures. Site-specific monitoring techniques include field observation and the use of various ground motion

  instruments, trip wires, radar, laser beams, and vibration meters. Data from these devices can be telemetered for real-time

  warning.
• 5. Landslide insurance and compensation for losses. Landslide insurance would be a logical means to provide

  compensation and incentive to avoid or mitigate the hazard. Landslide insurance coverage could be made a requirement

  for mortgage loans. Controls on building, development, and property maintenance would need to accompany the

  mandatory insurance. Insurance and appropriate government intervention can work together, each complementing the

  other in reducing losses and compensating victims.