March Monthly Exam

• Landslide is also called landslip
• Landslide is a ground movement on a sloping terrain
• Water is a 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.
• The hazard of landslides can be induced further or aggravated by rain.
• Areas with tropical climates such as the Philippines experience prolonged rain especially during the wet season.
• Landslides do not happen on flat grounds. Because of the angle on the ground, gravity induces the land to move downward.
• A high vulnerability to rainfall-induced hazards is characterized by areas with steep slope, dense population, and denuded ground.
• Prolonged or frequent rain can saturate the topsoil and bedrock, making the soil foundation of buildings or structures weak.
• Without plants and trees whose roots can absorb water and hold the soil together, subsequent rain water can continue to loosen up the soils that anchor the buildings.
• Eventually a heavy downpour of rain can quickly destroy these buildings and communities, giving way to landslides, mudslides or mudflow.
• Sinkholes are depressions or holes on the ground that resulted from the collapse of the surface layer of the soil
• Sinkholes occur in areas where the soil foundation is made of soft minerals and rocks such as limestone, salt beds or any acidic rocks.
• The rocks can be weakened further by frequent submersion in water, such as when there is repeated rainfall or unmanaged flood.
• The depth of sinkholes varies from a few meters to even kilometres deep.
• The rocks dissolve in water and gradually weaken, carving and forming spaces and underground passages for water. When the spaces underground become bigger and the layer of bedrock above it can no longer support the weight above it, a sudden collapse of the land surface dramatically takes place.
• The collapse of the ground can also be triggered by any type of land movement that cause vibrations such as earthquakes, volcanic activities and even human development activities such as construction and industrial activities.
• Most of the new sinkholes recently discovered are linked to land-use practices, especially groundwater pumping, ground excavation and land development.
• The topmost layer of the ground that covers the whole or cavity is maintained by the pressure of the groundwater.
• The top layer should not be built on by anything heavy or should not be even modified or touched at all.
• In urban development, however, ground modification cannot be prevented.
• 1. Springs, water seepage or water saturated grounds in areas that are not typically wet.

  2. Soil that loosens and moves away from foundations.

  3. New cracks or unusual bulges on cemented ground or walls.

  4. Underground utility lines that are broken due to vibration or tremors from the surface of the ground.

  5. Buildings, poles, walls and fences that are leaning.

  6. Sudden rapid flow of creek waters carrying more silted water.
• 1. For sinkholes, there are signs of an imminent danger in groundwater that does not provide the same amount and quality as before or has become cloudy, acidic, silted or soiled.

  2. Sign posts or poles that are leaning, slumping, sagging, slanting or bent.

  3. Ponds that have recently formed or puddles that grow or have never disappeared.
• Abney level or a laser rangefinder equipped with a tilt meter — used to measure the slope angle, soil compaction and soil strength of an area. The data determine the level of risk to landslides. The same data can also be used for future terrain alterations or guide to urban planners to plan a safer structural development in any area.
• Ground-penetrating radar or GPR — provide images of subsurface ground. It can detect the type of objects, changes in materials and void and cracks under a layer of soil; determining whether the sinkholes may occur or not because of the relatively accurate determination of the soft ground underlying the ground surface.
• Good penetration is achieved in soft layers or porous material such as dry sandy soils or massive dry materials such as lime stone. The measurement can reach up to 15 meters.
• 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.
• Dark shaded areas of the map indicate the highest susceptibility to landslides. Moderate susceptibility is green while low is yellow.
• 1. Plant more trees, grasses and other vegetation to prevent erosion and for compaction of soil.
  2. Build channels for diversion of mudflow or debris flow to direct the flow away from your property. Make sure though that the diversion does not affect your neighbor or any property and/or cause more significant damage as a result.
  3. Do not build your house on or near steep slopes, mountain edges, drainages or natural erosion valleys.
• BEFORE A LANDSLIDE

  1. Be familiar with your  surroundings. Watch for any changes in appearance or positions of theses objects. When there is a sudden debris and ri flow, this could be a good indicator of an incoming landslide.
  2. Avoid open storm-water drainage and run off as these areas are likely to receive debris and soil from higher elevations, especially if there is a storm or heavy rainfall.
  3. Be updated on news regarding the condition of your area. Be aware of the disaster plans of your local government.
  4. Learn and participate in an emergency response and evacuation plans for your community.
• DURING A LANDSLIDE

  1. Be attentive to unusual sound such as cracking objects, moving debris and rolling boulders.
  2. Stay away from the path of debris. This is more dangerous if mudflow occurs because it increases in strengths as it meets more water from ponds or streams and it could be aggravated by heavy rains.
  3. Stay on an elevated and sturdy area. Avoid low-lying area and steep slopes.
  4. If escape is not possible, curl into a tight ball and protect your head. Find a structure that can serve to protect you from the flow of debris.
• AFTER A LANDSLIDE

  1. Avoid the slide area. There is still danger of more landslides.
  2. Listen for the latest emergency information. Follow warning and instructions by the local government.
  3. If landslide is caused by rainfall, watch out for flooding as it will follow the same path taken by the debris flow.
  4. Check for injured or trapped people near the slide, and for damaged structures and other potential hazards. Report these immediately to the rescuers and authorities.
• 1. Find refuge in a stable ground or open area.
  2. Wait until the structures on and around the sinkhole stops moving. Do not attempt to go back and retrieve your belongings.

  3. Wait for the local government announcement when it is safe to go back.

   
• AFTER A SINKHOLE APPEARANCE

  1. Stay away from the sinkhole.
  2. Monitor the damages on objects. For example if the crack gets longer and wider, the sinkhole may be enlarging.
  3. Do not throw anything in a sinkhole. Anything throw into it may contaminated groundwater.
  4. Secure whenever is left of your properties and relocate to safe grounds, preferably far from this location because the same bedrock or soil profile may characterized the vicinities of the sinkhole.
• The Philippine is in the Northern Hemisphere, which is above the equator known as the Intertropical Convergence Zone (ITCZ) is where the trade winds meets.
• ITCZ is a narrow zone near the equator where northern and southern air masses converge, typically producing low atmospheric pressure.
• The ITCZ is responsible for the wet and dry season in the tropics.
• Trade winds flow in opposite directions and this is the reason that strong swirling of wind happens. As a result of this swirling movement, frequent natural hazards in the atmosphere and oceans takes place.
• ITCZ is the region that circles the Earth, near the equator, where the trade winds of Northern and Southern Hemisphere come together.