Hazards

• Hazard

  An extreme natural event that can cause loss of life, extreme damage to property and disrupt human activity
• Types of hazards

  • Geophysical
  • Hydrological
  • Atmospheric
• Characteristics of hazards

  • Clear origins or causes
  • Distinctive effects
  • Little or no warning
  • Exposure may be involuntary
  • Damage takes place shortly after the hazard, but impacts may last long into the future
  • Scale and impact requires an emergency response
• Disaster

  When a hazardous event and a vulnerable population combine
• There is no universal agreement on the difference between a disaster and a hazard</b>
• A natural hazard only has the potential to cause loss of human life, when it does not it is just a natural event
• The UN's criteria for it to be classified as a disaster are: 10+ people killed, 100+ are affected, a state of emergency is declared or international assistance is called for
• In 1990, Swiss Re Insurance defined a disaster as an event where at least 20 people die, or insured damage of at least $16 million USD is caused
• Disaster

  Causes 'significant' impact on a vulnerable population
• Factors influencing the relationship between a hazard and a disaster

  • Natural
  • Economic
  • Social
  • Political
  • Geographical
  • Technological
  • Environmental
• Natural factors

  • Magnitude
  • Frequency
  • Duration
  • Areal extent
  • Spatial concentration
  • Speed of onset
  • Regularity
• Earthquake magnitude is now measured in Moment Magnitude Scale (MMS), a modification of the earlier Richter scale
• The extent of damage from earthquakes is measured with the Mercalli Scale
• Volcano magnitude is measured using the VEI Index, related to the type of lava (basaltic or andesitic) and the type of boundary
• Hurricanes are measured using the Saffir-Simpson Hurricane Scale, which measures from 1 to 5, 5 the most severe, based on peak wind speeds
• People living in the Asia-Pacific region are 5x more likely to be affected by a natural disaster than those elsewhere
• Between 1995 and 2015, America, China and India had the most natural disasters
• The annual number of disasters has been rapidly increasing since 1900, peaking at over 400 many years since 2000
• Droughts caused the most deaths in the early 20th century, such as the 1928 Chinese Drought killing 3 million
• Deaths from natural disasters have been decreasing since the 1920s
• Hazard perception

  • Acceptance
  • Fear
  • Adaption
  • Fatalism
• Examples of hazard perception

  • 30% of Americans cite climate change as a motivator to move in 2023
  • Japan has put up sea walls after the 2011 earthquake
  • Only 4,000 people moved back to Paradise after the 2018 wildfire
• Responses to hazards and management

  • Modifying the loss (adaptation)
  • Modify vulnerability (adaptation)
  • Modify the event (mitigation)
  • Modify the cause (mitigation)
• Hazard Management Cycle


  A general plan for recovery and preparation for a hazard
• Park Model / Disaster Management Curve


  Useful to compare and contrast different hazards and pinpoint different responses needed at different stages
• The Hazard Management Cycle and Park Model / Disaster Management Curve are generalised and do not account for differences in development or the fact that some places may never return to 'normal'
• Plate tectonic theory


  The Earth's crust is split into 7 large plates and several smaller ones, all of which slowly move along Earth's surface
• Evidence of continental drift


  • The east coast of South America and West Africa seem to fit together
  • Rock layers in the Appalachian Mountains match those of the Caledonian Mountains in Scotland
  • Rocks in Alaska have fossils of palm tree leaves despite the cold climate, suggesting it was once at lower latitudes and more tropical
  • Karoo strata in South Africa match the Santa Catarina rocks in Brazil
• Paleomagnetism


  Provides evidence of seafloor spreading by examining the polarity of rocks
• Convection currents

  Heat from the core heats the base of the mantle, causing hot rock to rise, cool, and sink, repeating the process and moving the plates
• Gravitational sliding


  Ridge push and slab pull, where the force of gravity moves the plates
• Parts of Earth


  • Crust
  • Lithosphere
  • Asthenosphere
  • Mantle
  • Outer core
  • Inner core
• Continental vs oceanic crust

  • Continental
  • Oceanic
• Types of plate boundaries

  • Destructive
  • Constructive
  • Conservative
  • Collision
• The vast majority of earthquakes happen at plate boundaries
• Richter scale

  Measures maximum wave amplitude, not total energy released
• Moment magnitude (Mw)

  Measures the energy released and the amount of movement by rock and the area of the fault
• Mercalli scale


  Measures the intensity of the earthquake event
• Types of waves


  • Primary waves (P waves)
  • Secondary waves (S waves)
  • Love wave
  • Rayleigh wave
• Locating earthquakes


  The time between first P and S waves on a seismogram is used to determine the distance from the epicentre