[1.4] Natural Disasters in the Philippines

• natural disasters

  • Adverse events brought by the natural processes of the earth.
  • Its origins may be atmospheric, geological, or hydrological
• natural disasters experienced in the Philippines

  • earthquakes
  • floods
  • typhoons
  • volcanic eruptions
  • tsunamis
  • landslides
• earthquakes


  Weak or violent shaking of the ground due to the sudden movement of rock materials below the surface of the earth.
• hypocenter


  the point within the earth where an earthquake rupture starts
• epicenter


  the point directly above it at the surface of the Earth
• magnitude


  calculated through an instrument called a seismograph
• seismograph


  instrument used to calculate the magnitude
• Magnitude is represented by Arabic Numbers.
• intensity


  refers to the strength of an earthquake as perceived and felt by people in a certain locality
• Intensity is represented by Roman Numerals.
• Intensity Scale: I (use Roman Numerals)

  Shaking: Scarcely Perceptible


  Perceptible to people under favorable circumstances. Delicately balanced objects are disturbed slightly. Still Water in containers oscillates slowly.
• Intensity Scale: II (use Roman Numerals)

  Shaking: Slightly Felt


  Felt by few individuals at rest indoors. Hanging objects swing slightly. Still Water in containers oscillates noticeably.
• Intensity Scale: III (use Roman Numerals)

  Shaking: Weak



  Felt by many people indoors, especially on the upper floors of buildings. Vibration is felt like one passing of a light truck. Dizziness and nausea are experienced by some people. Hanging objects swing moderately. Still water in containers oscillates moderately.
• Intensity Scale: IV (use Roman Numerals)

  Shaking: Moderately Strong


  Felt generally by people indoors and by some people outdoors. Light sleepers are awakened. Vibration is felt like the passing of a heavy truck. Hanging objects swing considerably. Dinner, plates, glasses, windows, and doors rattle. Floors and walls of wood-framed buildings creak. Standing motor cars may rock slightly. Liquids in containers are slightly disturbed. Water in containers oscillates strongly. A rumbling sound may sometimes be heard.
• Intensity Scale: V (use Roman Numerals)

  Shaking: Strong


  Generally felt by most people indoors and outdoors. Many sleeping people are awakened. Some are frightened, and some run outdoors. Strong shaking and rocking were felt throughout the building. Hanging objects swing violently. Dining utensils clatter and clink; some are broken. Small, light, and unstable objects may fall or overturn. Liquids spill from filled open containers. Standing vehicles rock noticeably. The shaking of leaves and twigs of trees are noticeable.
• Intensity Scale: VI (use Roman Numerals)

  Shaking: Very Strong


  Many people are frightened; many run outdoors. Some people lose their balance. motorists feel like driving with flat tires. Heavy objects or furniture move or may be shifted. Small church bells may ring. Wall plaster may crack. Very old or poorly built houses and man-made structures are slightly damaged though well-built structures are not affected. Limited rockfalls and rolling boulders occur in hilly to mountainous areas and escarpments. Trees are noticeably shaken.
• Intensity Scale: VII (use Roman Numerals)

  Shaking: Destructive


  Most people are frightened and run outdoors. People find it difficult to stand on the upper floors. Heavy objects and furniture overturn or topple. Big church bells may ring. Old or poorly built structures suffer considerable damage. Some well-built structures are slightly damaged. Some cracks may appear on dikes, fish ponds, road surfaces, or concrete hollow block walls. Limited liquefaction, lateral spreading, and landslides are observed. Trees are shaken strongly.
• liquefaction


  process by which loose saturated sand loses strength during an earthquake and behaves like liquid
• Intensity Scale: VIII (use Roman Numerals)

  Shaking: Very Destructive


  Many well-built buildings are considerably damaged. Concrete dikes and foundations of bridges are destroyed by ground settling or toppling. Railway tracks are bent or broken. Tombstones may be displaced, twisted, or overturned. Liquefaction and lateral spreading cause man-made structures to sink, tilt, or topple. Numerous landslides and rockfalls occur in mountainous and hilly areas. Boulders are thrown out from their positions, particularly near the epicenter. Fissures and faults rapture may be observed.
• Intensity Scale: IX (use Roman Numerals)

  Shaking: Devastating


  People are forcibly thrown to the ground. Many cry and shake with fear. Most buildings are totally damaged. bridges and elevated concrete structures are toppled or destroyed. Numerous utility posts, towers, and monuments are tilted, toppled, or broken. Water sewer pipes are bent, twisted, or broken. Landslides and liquefaction with lateral spreading and sand boils are widespread. the ground is distorted into undulations. Boulders are commonly thrown out. River water splashes violently on slops over dikes and banks.
• Intensity Scale: X (use Roman Numerals)

  Shaking: Completely Devastating


  Practically all man-made structures are destroyed. Massive landslides and liquefaction, large-scale subsidence and uplifting of land forms, and many ground fissures are observed. Changes in river courses and destructive seiches in large lakes occur. Many trees are toppled, broken, and uprooted.
• flood


  a rise, usually brief, in the water level in a stream to a peak from which the water level recedes at a slower rate
• causes of floods

  • natural
  • artificial
• meteorological events

  • An intense and prolonged rainfall spells.
  • Unusually high coastal and estuarine waters due to storm surges, seiches, etc.
• seismic activities

  • Tsunamis (seismic sea waves).
  • Sinking of land due to earthquakes reduces the elevation of land areas.
  • The uplifting of lake and river beds from seismic causes sometimes results in the overflowing of these bodies of water.
• astronomically-influenced phenomena

  • High tides coinciding with the occurrence of heavy rainfall.
• blasting

  • Causes landslides in the slopes of hills and mountains which may result in the unintentional damming of rivers and streams.
• construction of temporary dams

  • Produces an impediment to the flow of a river or stream which then results in an overflow.
• failure of hydraulic and other control structures

  • Accidents like the breaking of a dike result in the entry of an enormous quantity of water into a protected area.
• mismanagement of hydraulic structures

  • May necessitate an untimely and sudden release of large amounts of excess water.
• denudation of forest and watershed areas

  • Alter the ecological system in a river basin will have an impact on the hydrology of the catchment.
• types of floods

  • minor flooding
  • major flooding
  • flash flood
• minor flooding


  Floodwater is usually shallow and there may not be a perceptible flow.
• major flooding


  Flooding is relatively deep in most parts of the stricken areas and there is a highly perceptible current as the flood spreads to other areas.
• flash flood


  Develops in less than six hours due to the extremely short concentration time of the drainage catchment in hilly and mountainous terrains where the slope of the river is rather steep.
• typhoon


  a mature tropical cyclone that usually develops in the Pacific Ocean
• Pacific Ocean


  where typhoons are usually developed
• tropical depression


  A tropical cyclone with maximum sustained winds of up to 61 kilometers per hour (kph) or less than 33 nautical miles per hour (knots).
• tropical storm


  A tropical cyclone with a maximum wind speed of 62 to 88 kph or 34 - 47 knots.
• severe tropical storm


  A tropical cyclone with a maximum wind speed of 89 to 117 kph or 48 - 63 knots.