Geophysical Hazards

• Hazard- a perceived event that is a potential threat to both human and property
• Geophysical- hazards coused by land processes (e.g. volcanoes)
• Atmospheric- hazards caused by atmospheric processes and the conditions created by these (e.g. tropical storms )
• Atmospheric- hazards caused by the atmosphere, such as tornadoes, hurricanes, and lightning
• Hydrological- hazards caused by water processes (e.g. floods)
• Perceptions of hazards are dependant on lifestyle factors: socio-economic factors; past experience; education; and religion
• People can have either passive responses (fatalism and fear) or active responses to hazards (prediction, adaptation, mitigation, management and risk sharing)
• fatalism- a view that people cant influence the outcome of a natural event and therefore, nothing can be done to mitigate against them.
• Fear- people feel so vulnerable to a hazard that they cant live in that area and move to unaffected regions.
• Prediction- using scientific research and past events to deliver warnings to reduce impacts.
• Adaptation- attempting to live with hazards by adjusting lifestyle choices to reduce potential losses (e.g. earthquake drills)
• Mitigation- working to lessen the severity of a hazard or preventing its occurrence (e.g. sea walls)
• Management- analysing potential risks and implementing a coordinated approach to manage and reduce risks.
• Risk sharing- the community shares the risk posed by hazrads and invests collectively to mitigate against the impacts of future hazards. (e.g. home insurance)
• Many factors influence how people respond to hazards: frequency, distribution, intensity/magnitude, level of development.
• Distribution- where hazards occur: areas of high hazrad distribution are likely to have a lot of managment strategies (e.g. Japan investment in aseismic buildings)
• Park model- shows how people's QoL is affected by hazards and how people respond (relief, rehabilitation, reconstruction) steepness of cure shows how quickly an area recovers, depth shows the scale of the disaster.
• Relief- immediate local response (e.g. search and rescue)
• Rehabilitation- temporary restoration of services and infrastructure (e.g. temporary shelters) in first days and weeks.
• Reconstruction- permanent restoration which aims to provide the same or improved QoL than before (aseismic designs of buildings)
• Hazard management cycle- shows how the events of one hazard inform planning and preparation for the next hazard (preparedness, response, recovery, mitigation)
• Inner core:

  -solid ball

  -iron and nickle

  -radioactive decay of uranium, responsible for internal energy
• Outer core:

  • semi-molten
  • liquid iron and nickel
• Lower mantle:

  • hot and dense solid rock due to intense pressure
  • high in silicon
• Asthenosphere:

  • semi-molten plastic-type layer
  • moves due to convection currents powered by heat from the core
• Lithosphere: the rigid outer part of the earth, consisting of the crust and upper mantle
• Continental crust:

  • thicker (30-70km)
  • less dense
  • composed of granite
• Oceanic crust:

  • thinner (7-10km)
  • denser (undergoes subduction)
  • composed of basalt
• Alfred Wegner proposed the theory of continental drift; that the continents were once joined together and then separate in 1912 but was unable to suggest why
• Harry Hess found evidence of sea-flier spreading through palaeomagnetism.
• Gravitational sliding/ Ridge push:

  • constructive plate margin
  • magma rises to the surface forming new crust which expands above the surface forming an ocean ridge 2-3km above the floor
  • new crust cools and becomes denser, gravity causes it to move downslope
  • this puts pressure on the plates causing shallow earthquakes
• Slab pull:

  • Destructive plate margins
  • cold, dense oceanic plate subducts into the mantle due to its own weight
  • the sinking of the plate edge pulls the rest of the plate with it
• Convection currents:

  • lower parts of asthenosphere heat up become less dense and rise
  • cool down as they get further from the core, become denser and sink
  • the currents drag the base of plates causing them to move
• Sea-floor spreading:

  as plates diverge, magma rises and cools to form new crust causing the sea floor to get wider

  • creates mid-ocean ridges
• Destructive Oceanic-Continental:

  • (e.g. Peru-Chile)
  • denser oceanic crust subducts forming a deep sea trench (e.g. Marianas Trench)
  • oceanic crust heated by friction and melts into magma, which is less dense than continental so rises to form volcanoes
  • as one plate moves they can get stuck forming earthquakes
• Destructive Oceanic-Oceanic:

  • denser will subduct forming a deep-sea trench, earthquakes and volcanoes
  • volcanic eruptions underwater create island arcs (e.g. Mariana Islands)
• Destructive Continental-Continental:

  • neither is subducts as same density so no earthquakes or volcanoes
  • any sediment in between buckles forming fold mountains (e.g. Himalayas)
• Basaltic lava:

  • most abundant
  • comes from shield volcanoes
  • low viscosity
  • fast flowing
  • 52% SiO2 and high Fe and Mg content
• Andesitic lava:

  • strata volcanoes (composite)
  • higher viscosity than basaltic
  • slow flowing
  • lava domes commonly produced
• Rhyolitic lava:

  • composite volcanoes
  • highest viscosity
  • slowest flowing
  • greatest SiO2 content (68%)