Hazards

• Hazard


  A potential threat to human life and property caused by an event
• Major types of geographical hazard


  • Geophysical
  • Atmospheric
  • Hydrological
• Atmospheric hazards


  • Caused by atmospheric processes and the conditions created because of these, such as weather systems (e.g. wildfires)
• Hydrological hazards


  • Caused by water bodies and movement (e.g. floods)
• Incidence


  Frequency of a hazard
• Intensity


  The power of a hazard i.e. how strong it is
• Magnitude


  The size of the hazard, usually this is how a hazard's intensity is measured
• Fatalism


  The viewpoint that hazards are uncontrollable natural events, and any losses should be accepted as there is nothing that can be done to stop them
• Prediction


  Using scientific research and past events in order to know when a hazard will take place, so that warnings may be delivered and impacts of the hazard can be reduced. In some cases, hazards may also be prevented when predicted early enough.
• Mitigation


  Strategies carried out to lessen the severity of a hazard
• Management


  Coordinated strategies to reduce a hazard's effects. This includes prediction, adaptation, mitigation.

  
• Risk sharing


  A form of community preparedness, whereby the community shares the risk posed by a natural hazard and invests collectively to mitigate the impacts of future hazards.
• The Park Model


  • Graphical representation of steps carried out in hazard recovery
  • Rough indication of time frame
  • Can be used in comparing hazardous events
  • The steepness of the curve shows how quickly an area deteriorates and recovers
  • The depth of the curve shows the scale of the disaster
• The Park Model of Human Response to Hazards


  1. Relief (hours-days)

  2. Rehabilitation (days-weeks)

  3. Reconstruction (weeks-years)
• The Hazard Management Cycle

  1. Preparedness

  2. Response

  3. Recovery

  4. Mitigation

  
• Structure of the Earth

  • Inner core: Solid ball of iron/nickel, very hot due to pressure and radioactive decay
  • Outer core: Semi-molten, iron/nickel
  • Mantle: Mainly solid, rocks high in silicon
  • Asthenosphere: Semi-molten, moves due to convection currents powered by heat from core
  • Lithosphere: Broken up into plates
  • Crust: The thin top of the lithosphere, oceanic crust is dense and is destroyed by plate movement, continental crust is less dense and is not destroyed

  
• Different plate boundaries


  1. Destructive plate margin

  2. Constructive plate margin

  3. Conservative plate margin

  
• Destructive plate boundaries


  • Continental and oceanic: Denser oceanic plate subducts below the continental, leaving a deep ocean trench, built up pressure causes explosive volcanoes
  • Oceanic and oceanic: Heavier plate subducts leaving an ocean trench, built up pressure causes underwater volcanoes, lava cools and creates new land called island arcs
  • Continental and continental: Both plates are not as dense as oceanic so lots of pressure builds, ancient oceanic crust is subducted slightly but there is no subduction of continental crust, pile up of continental crust on top of lithosphere due to pressure between plates, fold mountains formed

  
• Constructive plate boundaries


  • Oceanic and oceanic: Magma rises in between the gap left by the two plates separating, forming new land when it cools, less explosive underwater volcanoes formed as magma rises, new land forming on the ocean floor by lava filling the gaps is known as sea floor spreading
  • Continental to continental: Any land in the middle of the separation is forced apart, causing a rift valley, volcanoes form where the magma rises, eventually the gap will most likely fill with water and separate completely from the main island
• Ridge push


  The slope created when plates move apart has gravity acting upon it as it is at a higher elevation. Gravity pushes the plates further away, widening the gap (as this movement is influenced by gravity, it is known as gravitational sliding).

  
• Hotspots


  Areas of volcanic activity that are not related to plate boundaries. Hot magma plumes from the mantle rise and burn through weaker parts of the crust, creating volcanoes and islands. The plume stays in the same place but the plates continue to move, which sometimes causes a chain of islands.
• Volcanic hazards


  • Spatial distribution: Along constructive or destructive plate boundaries, or located on hotspots
  • Magnitude: Vulcanicity is measured using the Volcanic Explosivity Index, the more powerful, the more explosive
  • Frequency: Volcanoes are classed as either active, dormant or extinct, an estimated 50-60 volcanoes erupt each month
  • Regularity: Volcanic eruptions are regular in that the eruptions on each type of boundary are similar, sometimes eruptions may be irregular and not fit patterns
  • Predictability: Regularity of eruptions can help estimate when eruptions will take place, but there is no definite predictions to a volcanic eruption

  
• Hazards caused by volcanoes


  • Lava flows
  • Lahars (mudflows)
  • Floods
  • Tephra
  • Toxic gases
  • Acid rain
  • Nuées ardentes/pyroclastic
• Volcanic eruptions


  • Regular - eruptions on each type of boundary are similar (e.g. eruptions on destructive boundaries will regularly be more explosive than at constructive boundaries)
  • Irregular - eruptions may not fit patterns

  
• Predictability of volcanic eruptions


  • Regularity of eruptions can help estimate when eruptions will take place (i.e. every 10 years)
  • Seismic activity, gases releasing, elevation etc. can all indicate an imminent eruption, but there is no definite predictions to a volcanic eruption

  
• Hazards caused by volcanoes


  • Lava flows
  • Lahars (mudflows) - caused by a number of reasons, usually by melting ice at high latitudes
  • Floods - from melting ice sheets or glaciers at high latitudes
  • Tephra - any type of rock that is ejected by a volcano
  • Toxic gases - released during some eruptions
  • Acid rain - caused when gases such as sulfur dioxide are released into the atmosphere
  • Nuées ardentes/pyroclastic flows - clouds of burning hot ash and gas that collapses down a volcano at high speeds
• Primary effects


  • Ecosystems damaged through various volcanic hazards
  • Wildlife killed
  • Businesses and industries destroyed or disrupted
  • People killed
  • Homes destroyed from lava/pyroclastic flows
  • Government buildings and other important areas destroyed or disrupted
• Secondary effects


  • Water acidified by acid rain
  • Volcanic gases contribute to greenhouse effect (global warming)
  • Jobs lost
  • Profit from tourism industry
  • Fires can start which puts lives at risk
  • Mudflows or floods
  • Trauma
  • Homelessness
  • Conflicts concerning government response, food shortages, insurance etc.
• Responses to volcanic hazards


  • Preventing them directly
  • Being prepared for the next hazard
  • Mitigating the effects of the hazard
  • Completely adapting your lifestyle to limit the hazard's effects
• Plates do not move in fluid motions
• Seismic events


  • At any boundaries, plates become stuck due to the friction between plates
  • The pressure builds so much that it cannot be sustained and the plates eventually give way
  • The pressure is released quickly, causing a jolting motion in the plates
  • This jolt is responsible for seismic movement spreading throughout the ground
  • The focus is the point underground where the earthquake originates from
• Spatial distribution of seismic events

  Along all boundaries
• Magnitude of seismic events


  • Seismicity is measured using the logarithmic Richter Scale which is a measure of the strength of seismic waves
  • The Mercalli Scale is also used, which is a rate of the destruction caused
• Frequency of seismic events


  • Earthquakes are frequent around the world and occur every day at boundaries
  • Hundreds of smaller magnitude earthquakes that cannot be felt by humans occur every day, whereas the larger earthquakes are less frequent
• Regularity of seismic events

  Earthquakes follow no pattern and are random so there is irregularity between events
• Predictability of seismic events

  • Earthquakes are almost impossible to predict
  • Microquakes may give some indication but the magnitude cannot be predicted as how strong they are is random
• Hazards caused by seismic events


  • Shockwaves (seismic waves) - energy released from the sudden jolt that vibrates through the ground
  • Tsunamis - caused when water is displaced from plates moving underwater, creating a large wave
  • Liquefaction - When soil is saturated, the vibrations of an earthquake cause it to act like a liquid
  • Landslides and avalanches
• Primary effects of seismic hazards


  • Earthquake can cause fault lines which destroy the environment
  • Liquefaction
  • Businesses destroyed
  • Buildings collapse, killing/injuring people and trapping them
  • Government buildings destroyed
• Secondary effects of seismic hazards


  • Radioactive materials and other dangerous substances leaked from power plants
  • Saltwater from tsunamis flood freshwater ecosystems
  • Soil salinisation
  • Economic decline as businesses are destroyed (tax breaks etc.)
  • High cost of rebuilding and insurance payout
  • Sources of income lost
  • Gas pipes rupture, starting fires which can kill
  • Water supplies are contaminated as pipes burst, spreading disease and causing floods
  • Tsunamis which lead to damaging flooding
  • Political unrest from food shortages or water shortages
  • Borrowing money for international aid
  • Can be initial chaos and 'lawlessness' e.g. looting
• Tropical storm


  A low pressure, spinning storm with high winds and torrential rain