Restless Earth

Restless Earth

The Earth
1. Lithosphere
  1. Continental Crust
    1. Solid
      1. Granite
        Up to 900 degrees
    2. Makes up most of the land area of the Earth
      1. Between 25-80 km thick
  2. Oceanic Crust
    1. Solid
      1. Basalt
        Up to 900 degrees
    2. 6-8 km thick
2. Mantle
  1. Asthenosphere
    1. Partially Molten
      1. Periodotites
        1000-1600 degrees
  2. Mantle
    1. Solid
      1. Silica-based minerals
        1600-4000 degrees
3. Core
  1. Outer core
    1. Liquid:Very dense
      1. Iron/Nickel
        4000-5000 degrees
  2. Inner core
    1. Solid: Very dense
      1. Iron/Nickel
        4000-5000 degrees
Tectonic Activity
1. High temperatures in the core are caused by radioactive decay
  1. These create rising limbs of material, called convection currents.
    1. These cool and spread out as they rise before sinking again
      1. Some of this material moves in sheets creating movement in the crust
        This is pulled apart, creating new crust
        In some places it rises, creating hotspots.
Plate Boundaries
1. Destructive Margins
  1. Where Oceanic plates collide with Continental plates
    1. The denser basaltic oceanic plate sinks beneath the constructive
      1. This is subduction
        This creates a deep ocean trench
        As the oceanic plate is subducted into the mantle, pressure and temperature increase.
        Lightweight materials rise to the surface, forming volcanoes
        Long chains of volcanoes (volcanic arcs) are located about subducted plates
        Usually above where plates have reached a depth of 100 km
        The collision also lifts and buckles the continental plate
        This creates fold mountains
    2. EG: Nazca and South American Plates
2. Constructive Margins
  1. Formed by rising magma splitting the continental crust, forming new oceans,
    1. EG: Mid-Atlantic Ridge
3. Conservative Margins
  1. Where plates slide past each other or move in the same direction at different speeds.
    1. No crust is formed or destroyed
      1. No volcanoes formed
    2. Causes strain
      1. Earthquakes are frequent and often large
        EG: San Andreas Fault
Hazards and Causes
1. Impacts depend on
  1. Size of event
  2. Vulnerability of population
  3. How prepared the country was
2. Where they occur
  1. Volcanic eruptions generate earthquakes
  2. Earthquakes occur on conservative margins
  3. Not all volcanoes or earthquakes occur on plate boundaries
    1. Some do so at hotspots
3. Types of Volcano
  1. Composite
    1. Steep sided, small area, alternate layers of ash and lava
      1. Viscous/sticky
      2. Flows Slowly
      3. Often freezes in central vent
      4. Granatic or andesitic magma
      5. Infrequent unpredictable explosions
      6. Pressure builds up over time
  2. Shield
    1. Gentle slopes
    2. Large area
    3. Almost all lava
    4. Fluid flows quickly from many fissures
    5. Basaltic magma
    6. Very frequent gentle eruptions
4. Earthquakes can't be predicted so are genererally more dangerous
  1. Both volcanoes and earthquakes can cause tsunamis
    1. Tsunamis
      1. Are a series of destructive ocean waves
        Travel at up to 900 km /h
        Can be up to 20-30 m high
        EG: Indian Ocean tsunami of 2004 26th December killed 250,000 people in 14 countries.
5. Impacts of Earthquakes
  1. Factors controlling the severity
    1. The magnitude of the Earthquake on the richter scale
    2. The depth. (Shallow are more destructive)
    3. The distance from the epicentre
    4. The time of day
    5. The level of preparedness
    6. Quality of emergency services
Predicting and Preparing for Hazards
1. Predicting
  1. Bulging of volcanoes can be measured
2. Preparing
  1. Tsunami warning sirens help evacuate people
  2. Evacuation routes can be planned
  3. Mitigation
    1. Hazard resistant buildings
      1. Make foundations deep but allow movement
      2. Build in shock absorbers
      3. Cross bracing prevents floors collapsing
      4. Reduce roof weight
      5. Use lighter bricks
      6. Strengthen wall corners with wire mesh and cement
    2. Disaster kits
    3. Landuse Planning

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