MODULE 4

• The Philippines is under continuous threat from various types of natural hazards
• Every Filipino must understand the science behind such phenomena
• Natural hazards discussed in this module

  • Earthquake
  • Volcanic
  • Landslide
  • Flood
• Body forces


  Forces acting within the Earth's interior
• Surface forces


  Forces acting on the Earth's surface
• Stress


  Force per unit area
• Strain


  Deformation of a material in response to stress
• Stages of deformation as stress increases

  • Elastic deformation
  • Plastic deformation
  • Fracture
• Brittle material


  Material that breaks or fractures when stressed
• Ductile material


  Material that deforms plastically when stressed
• Types of folding


  • Anticline
  • Syncline
  • Monocline
• Types of fault movement

  • Normal fault
  • Reverse fault
  • Strike-slip fault
• Epicenter


  Point on the Earth's surface directly above the focus of an earthquake
• Focus


  Point within the Earth where an earthquake originates
• Seismology


  Study of earthquakes and the propagation of seismic waves
• Types of seismic waves

  • Primary (P) waves
  • Secondary (S) waves
  • Surface waves
• Magnitude


  Measure of the energy released by an earthquake
• Intensity


  Measure of the shaking produced by an earthquake at a particular location
• Earthquake hazards


  • Ground shaking
  • Liquefaction
  • Landslides
  • Tsunamis
• Examples in the Philippines of earthquake hazards
• Earthquake hazard


  Potential for an earthquake to cause damage
• Earthquake risk


  Likelihood of an earthquake causing damage
• Factors determining intensity of ground shaking

  • Magnitude
  • Distance from epicenter
  • Local geology
• Paleoseismology


  Study of past earthquakes using geological evidence
• Seismic gaps


  Regions along a fault where no earthquakes have occurred for a long time
• Short-term prediction of earthquakes is unsuccessful
• Steps to mitigate earthquake impacts

  • Earthquake-resistant building design
  • Early warning systems
  • Disaster preparedness plans
• Steps to take before, during and after an earthquake

  • Before: Prepare emergency kit, identify safe places
  • During: Drop, cover, hold on
  • After: Check for injuries, turn off utilities, evacuate if necessary
• Most deaths from the volcanic eruptions discussed were caused by volcanic activity
• The eruptions discussed introduced scientists to new volcanic phenomena they had not previously observed or understood
• Major types of magma

  • Felsic
  • Intermediate
  • Mafic
• Major gases in magma

  • Water vapor
  • Carbon dioxide
  • Sulfur dioxide
• Viscosity


  Measure of a fluid's resistance to flow
• Block


  Large, angular fragment of rock ejected during a volcanic eruption
• Bomb


  Rounded, solidified fragment of lava ejected during a volcanic eruption
• Ash


  Fine fragments of rock, minerals, and volcanic glass ejected during a volcanic eruption
• Eruption column


  Vertical column of gas and ash erupted from a volcano
• Pyroclastic flow


  High-density mixture of hot gas and volcanic materials that travels rapidly down the slopes of a volcano
• Lateral blast


  Explosive outward movement of gas and rock from the side of a volcano
• Ash fall deposits can be distinguished from pyroclastic flow and surge deposits