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Geophysical hazards (KWH 2001) (Geophysical systems Big question: How do…

- - - - Caused by the high temperature
        at the core of the earth, plates are
        heated up, become less dense and
        rise. The same plate will lose heat
        when further away from the core
        and fall, which forms a convection current
    - - The plunging of one plate beneath another often due
        to collision of two plates. The denser plate will subduct
        under the less dense plate. Note:
        1) Oceanic subducts under continental
        2) Oceanic subducts under denser oceanic
        3) Continental does not subduct** when colliding
        with continental (both will fold instead)
    - - The core of the earth is about
        the temperature at the surface
        of the sun, at 5430 degree Celsius.
        This causes plates on at the surface
        of the earth to undergo convection
    - - A small area of unusually high heat flow.
        The high heat may cause plates to split
        apart, causing rifting. This can also cause
        hotspots (volcano that is not on plate
        boundary) to form. E.g. Hawaiian hotspot)
    - - Occurs at constructive plate
        boundaries (where land is formed) due
        continuous rift faulting and hardening
        of magma in the gaps formed.
  - - - 1) No explosive activity, no fragments
        ejected during eruption
        2) Non viscous, runny and hot lava rich
        with magnesium and iron when cooled
        3) Lava flows great distances and forms
        gently sloping sides, shallow crater and
        large circumference
    - - 1) Very explosive activity that will eject
        volcanic material during eruption (e.g.
        ash, sulfur, magma, crater materials)
        2) Made up of alternating layers of ash
        and cooled lava. Slope of 3 degree at top
        and 5 degree at the base.
        3) Very viscous lava that can clog the vent
        and increase pressure in the volcano.
    - - 1) Formed by accumulation of fragments
        of solid materials.
        2) Not very high, with an average height
        of 300 m
        3) Eruptions are violent, with cinders, ash
        and other fragments getting ejected.
    - - Lahars: Occurs when lava mixes with
        liquid, usually due to rain/water body near
        the volcano during eruption. Lahars can
        move up to 10 m/s and go up to 140 m deep
        Caused by: All three types of volcanoes
      - Pyroclastic flow: A fast-moving current of
        hot gas and volcanic matter that is capable
        of reaching speeds up to 700 km/h. The
        gases can reach temperatures of about 1,000 °C.
        Caused by: Strato volcano/Cinder volcano (small scale)
      - Landslides:Large masses of wet or dry
        rock and soil that fall rapidly. If the landslide
        is large enough and contains a high-enough
        percentage of water, it may transform into a lahar
        Caused by: Strato volcano
      - Small ash particles: Can travel up to 31 km
        radius away from the volcano. The small
        particles can enter the lungs and cause
        respiratory problems
  - - - Shallow-focus earthquakes:Occur
        relatively close to the ground surface.
        Deep-focus earthquakes: Occur at
        considerable depth under the ground.
        Shallow focus has potential to do more
        damage as less force generated is absorbed
        by overlaying material
    - - The point on the surface, directly above
        the center of the focus. This is the area
        where the earthquake is the strongest
        
        Diagram showing epicenter and focus
    - - P-waves: Longitudinal waves, travels the fastest
        and can travel through solids and liquids.
        S-waves (secondary wave): Transverse waves (distortional),
        travel slower than P waves and cannot travel through
        liquid. Cause more damage than P-waves
        Both waves can be transformed into Love and Rayleigh
        waves upon reaching the crust.
        Love waves: Causes crust to move sideways
        Rayleigh waves: Causes crust to move up and down
        Both waves travel slowly through the crust but cause
        the most damage.
    - - Tsunami
        
        Series of waves in a water body caused by
        the displacement of a large volume of water
        during an earthquake (can reach up to 3 m)
      - Transverse faults
        
        Occurs at a transform boundary, where
        the two plates slide past each other
      - Liquefaction
        
        Occurs when saturated soil substantially
        loses strength and stiffness in response
        to an applied stress during an earthquake
      - Landslide
        
        Large masses of wet or dry rock and
        soil that fall rapidly. Caused by too
        much sheer stress on the land mass
    - - Dam building/resource extraction (e.g. fracking)
        requires digging deep into the ground. The
        disposal of chemicals into deep wells in the
        ground can also destabalise rocks and reactivate
        underground faults
  - - - Affected by:
        1) Sheer strength
        Internal resistance of the slope. Can be increased
        through planting vegetation or using gabions
        2) Sheer stress
        Load that is placed on the slope. Increased by
        movement of the mass (e.g. earthquakes/volcano
        eruptions
- - - - 1) Levels of wealth and development
        Affects quality of life, ability to afford
        insurance and money to restore
        quality of life after a disaster.
        2) Construction styles and building codes
        3) Access to technology to predict and
        warn citizens of an incoming hazard for
        better preparation.
    - - 1) Nature of society: Ability of government
        to procure and administer aid during and
        after a geophysical event
        2) Effectiveness of lines of communication
        3) Availability and readiness of emergency
        personnel
    - - 1) Gender: Women are normally carers
        for their children/parents and may feel
        responsible for them after the disaster
        2) Education: Increases the awareness
        and potential impact of a hazard event.
        Drills are also important to prepare for
        the hazard event.
    - - 1) Population density
        2) Ratio of elderly and young children
        in the population
        3) Number of people who are disabled
        4) Migrants: Unfamiliarity with the location
        5) Cultural factors: Affects extent of trust
        in government, scientists and influential
        figures