Chapter 1 : Restless Earth

Chapter 1 : Restless Earth

1. Crust - made from thin layers of tectonic plates

   • Mantle - solid upper part and semi-liquid lower part that can flow
     • Core - consists of a liquid outer core and solid inner core
   • Continental crust (30-60km) is thicker than oceanic crust (6-8km)
     • Oceanic crust (3.3) is denser than continental (2.7)
       • Continental - made of granite
         • Oceanic - made of basalt rock

2. Lithosphere - uppermost layer of the earth(crust and solid top layer of the mantle)

   • Asthenoshpere - the upper past of the earth's mantle, where the rocks are more fluid

3. Convection currents

   • 1. The core heats the molten rock in the mantle
     • 2. Heated rock from the mantle rises to the earth's surface
       • 3. At the surface the convection current moves the tectonic plates in the crust
         • 4. Molten rock cools and flows back to the core to be reheated

4. The core

   • Made of Iron & Nickel
     • Heat created by radioactive elements e.g uranium and thorium
       • Outer is liquid. Inner is solid

5. Plate tectonics

   • Destructive plate Boundaries
     • Example: Nazca and South American Plate
       • 2 plates collide and the denser basaltic oceanic plate is subducted under the lighter granitic continental plate
         • Many earthquakes and volcanoes
   • Constructive plate boundaries
     • Example: Eurasian and North American plates
       • Rising convection currents pull oceanic crust apart forming volcanic ridge e.g. Miid-Atlantic ridge
   • Conservative plate boundaries
     • Example: San Andreas Fault, California
       • Two plates slide past each other - causes friction between plates - extreme stress build up in the crustal rocks
         • eventually released as an earthquake
   • Collision plate Boundary
     • Example:Indo-Australian and Eurasian plates
       • Two continental plates collide and the two plates buckle
         • Earthquakes are common
           • Buckling has led to fromation of the Himilayan chain
   • Aid for diasters
     • trained volunteers - clear debris
       • clean water - prevent disease spread
         • food
           • tents + blankets
     • radio communitcation
     • medical care
     • evacuation
       • refugees (forced to move due to natural hazard)

6. volcanoes

   • shield
     • found on constructive plate boundaries
       • thin, runny lava
         • Gentle sloping sides and a wide base
           • basaltic magma - very hot - low silica and gas content
             • erupt frequently but not violently
   • composite
     • desrtuctive plate boundaries
       • viscous, sticky lava and ash
         • steep sloping sides and narrow base
           • layers of thick lava and ash
             • andesitic magma - less hot - silica and gas
               • erupt infrequenly but violently, including pyroclastic flows (mix of gas, ash and rock)
   • Montserrat, 1995
     • Tiny caribbean island - 100km2
     • volcano been dormant sice 17th century
       • very viscous lava had blocked vent
     • large amounts of ash, lava and pyroclastic flows
       • Capital city, Plymouth covered in ash
         • now become a 'ghost town' - services have relocated
     • Impacts
     • Effects
       • social
         • Population was10,500 now 5,000
         • had to permanently relocate to the north after inital evacuation by government for protection
         • some emigrated to Antigua and further afield (secondary)
       • economic
         • primary impact on econmy - devastating
           • agriculture and tourism
             • both have now slowly recovered
             • destruction of most of the island's crops (ash) - primary
     • primary - destruction of forests - fires ignited by the gas

7. Tsunami

   • triggered by earthquake/volcanic eruption happens at sea.
     • Movement of plates makes all of the water on top of this sea bed rise up
       • 2 blocks of water which move in opposite directions away from the epicentre, as huge waves

8. Impacts

   • Primary - those that take place at the time of the event itself and are directly caused by it
     • e.g. Road cracks, building collapse, landslides
   • Secondary - those that follow the vent in the hours, days and weeks after and are indirectly caused by it
     • e.g fires break out, disease spread and food/water run short

9. Earthquakes

   • Damage and loss of life
     • depends on - type of hazard, place's vulnerability to hazard, the capacity to cope and recover
   • Kashmir, 2005
     • Magnitude- 7.6 (richter scale) Epicentre - Muzaffarabad Death toll - 75,000
       • Injured - 75,000 Homeless 2.8 million Property cost - $440 million
     • Remote mountainous area
     • Normal school day - many dead were children
       • Ramadan - Many sleeping after waking for pre-dawn meal
     • Primary - landslides, falling rock, large cracks in ground
       • Secondary - Broken sewage pipes contaminated water supply and spread disease and people died of cold during harsh winter
       • Impacts
     • responses
       • short term - the army/ emergency services, tents given out by charities, Aid workers form abroad to find surivors and treat injured
         • long term - schools and hospital rebuilt, building regulations improved - reduce damage and death toll for future earthquakes
   • How ready is San Francisco?
     • Disaster waiting to happen
       • Many faults threaten city
         • San andreas and hayward - most dangerous
     • costly to make old buildings safe
       • Many buildings and critical structures in the city - not adaquately upgraded to withstand earthquakes e.g biggest hospital san francisco general, schools, bay bridge and the golden-gate bridge
     • tension becuase city governement wants to reduce taxes and also be responsible
   • Earthquake proof buildings
     • MEDC
       • More money to spend
         • pendulum - stop building sway
           • cross bracing - stop floor collapse
             • deep steel foundations - prevent collapse
     • LEDC
       • Need to use cheaper material e.g timber
         • cross braced bamboo frame
           • lightweight thatch roof not mud
             • steel rods foundation

10. Volcanoes

    • Prediction
      • Tiltmeters (detect when a volcano swells)
        • Boreholes (measure water temp.)
          • Aircraft (measures the gas)
            • Seismometers (measure tremors and earthquakes)
              • Hot springs are monitored
    • Protection
      • concrete shelters
        • evacuation routes clearly signposted
          • Concrete lahar channels divert dangerous mudflows
            • Insurance is udes so any damage can be fixed and repaired