Geography topic 1

• Tectonic hazard

  Anything that threatens human life or infrastructure because of the processes of plate boundaries and the movement of them
• The most powerful earthquakes occur at conservative plate boundaries
• Ocean fracture zone (OFZ)

  Earthquake activity along mid-ocean ridges
• Continental fracture zone (CFZ)

  Earthquake activity along mountain ranges
• The Pacific Ring of Fire is a very active area for volcanoes and earthquakes
• Intraplate earthquakes

  Earthquakes that occur inside the plate margins, usually weaker
• Volcanic hotspots

  Fractures in the crust where there is a magma plume rising through, creating islands over time
• Constructive margins

  1. Plates move apart, allowing magma to rise

  2. Can be oceanic-oceanic or continental-continental

  3. Eruptions are usually effusive and not very damaging
• Destructive margins

  1. Oceanic plate subducts under continental plate

  2. Forms mountain ranges, large earthquakes, and violent volcanic eruptions

  3. Can also be oceanic-oceanic or continental-continental
• Conservative margins

  1. Plates slide past each other, causing frequent shallow earthquakes

  2. Only occur between oceanic and continental plates
• Earth structure

  Crust, lithosphere, asthenosphere, mantle, outer core, inner core
• Mantle convection

  Convection currents in the mantle that drive plate movement
• Alfred Wegener's theory of continental drift proposed that all continents were once part of a supercontinent called Pangea
• Paleomagnetism theory shows patterns of the Earth's magnetic field on the seafloor, proving seafloor spreading
• Subduction


  Denser oceanic plate sinks under lighter continental plate, causing earthquakes and volcanoes
• Gravitational sliding


  Occurs at constructive margins, where rising magma creates a slight slope for the plates to slide apart
• Slab pull

  The dense, cold oceanic plate pulls itself into the mantle as it subducts
• Constructive margin hazards

  1. Shallow, low-magnitude earthquakes

  2. Small, slow, effusive volcanoes with low gas content
• Destructive margin hazards

  1. Deep, high-magnitude earthquakes

  2. Violent, explosive volcanoes
• Plate boundary activities

  • Shallow earthquakes
  • Low magnitude earthquakes
  • Small, slow volcanoes
  • Low gas content volcanoes
  • High viscosity volcanoes
• Destructive margin (oceanic and continental)

  • Large earthquakes up to 9 magnitude
  • Frequent, violent volcanic eruptions
  • Composite volcanoes with high gas and silica content
• Destructive margin (oceanic and oceanic)

  • Frequent earthquakes but not as large as oceanic-continental
  • Violent volcanic eruptions
  • Creates volcanic islands
• Collisional margin (continental and continental)

  • Large shallow fault lines
  • High magnitude earthquakes
  • No volcanic eruptions
• Conservative margin

  • High magnitude shallow earthquakes
  • Very destructive
• Primary waves (P waves)

  Fastest seismic waves, cause least damage
• Secondary waves (S waves)

  Arrive after P waves, shake ground violently, cause damage
• Love waves (L waves)

  Arrive last, travel horizontally, cause significant damage including crustal fracturing
• Crustal fracturing


  • Buckling and cracking of Earth's surface, primary earthquake hazard
• Liquefaction


  • Soil loosening and water rising through cracks, secondary earthquake hazard
• Landslides


  • Soil and sediment dislodging and falling downhill, secondary earthquake hazard
• Pyroclastic flows


  • Dense, fast-moving, hot ash and gas clouds, primary volcanic hazard
• Ash fall


  • Ash particles falling and damaging vegetation, buildings, water sources, primary volcanic hazard
• Lava flows


  • Extensive areas covered in destructive lava, primary volcanic hazard
• Gas eruptions


  • Poisonous gases released, primary volcanic hazard
• Lahars


  • Volcanic mudflows, secondary volcanic hazard
• Jökulhlaups


  • Flooding from melting glaciers, secondary volcanic hazard
• Tsunami


  Large, fast-moving ocean waves caused by submarine earthquakes, volcanic eruptions, or landslides
• Earthquake is when two plates move past one another, causing friction between rocks which builds up energy until it suddenly releases as an earthquake.
• Natural hazard


  A natural event that has the potential to harm people, property, and society
• Natural disaster


  The realization or the impact of the natural hazard itself, the harm that has occurred and the damage that has been done