Tectonic hazards

• Tectonic plates


  Huge floating plates that make up the Earth's surface and are constantly moving
• Earth's surface divided into tectonic plates


  1. The Earth's crust (outer layer) is divided into slabs called tectonic plates

  2. Plates float on the mantle (layer of semi-molten rock)
• Types of crust


  • Continental crust (thicker, 30-50 km, less dense)
  • Oceanic crust (thinner, 5-10 km, more dense)
• Plates moving


  Caused by convection currents in the mantle
• Plate margins/boundaries


  Places where plates meet
• Types of plate margins

  • Destructive
  • Constructive
  • Conservative
• Destructive margins


  • Two plates moving towards each other
  • Oceanic plate subducted (forced down into mantle) and destroyed, creating gas-rich magma
  • Volcanoes and ocean trenches occur
• Destructive margin example


  • Nazca plate subducting beneath South American plate, creating Atacama Trench
• Constructive margins


  • Two plates moving away from each other
  • Magma rises from mantle to fill gap and cools, creating new crust
• Constructive margin example

  • Movement of Eurasian and North American plates forming mid-Atlantic ridge
• Conservative margins


  • Two plates moving sideways past each other or in same direction at different speeds
  • Crust isn't created or destroyed
• Conservative margin example


  • Pacific plate moving faster than North American plate at San Andreas Fault
• Volcanoes


  Form at destructive and constructive plate margins
• Volcanoes form at destructive margins

  Denser oceanic plate moves down into mantle, melts, and magma rises through cracks in crust, erupting as lava
• Volcanoes form at constructive margins

  Magma rises up into gap created by plates moving apart
• Other volcanoes


  Some form over hot spots in mantle, e.g. Hawaii
• Volcanic eruptions


  Emit lava and gases, some emit lots of ash that can cover land, block sun, and form pyroclastic flows
• Earthquakes


  Occur at all three types of plate margins
• Earthquakes occur


  Tension builds up at plate margins, plates eventually jerk past each other, sending out shock waves that are the earthquake
• Earthquake focus and epicentre

  Focus is point in Earth where earthquake starts, epicentre is point on surface directly above
• Moment magnitude scale


  Measures amount of energy released by earthquake, logarithmic scale so higher magnitude causes much more shaking
• Earthquakes of magnitude 6 and below normally only cause slight damage, 7 and above can cause major damage and deaths
• Tectonic hazards


  Effects and responses can vary depending on a country's wealth
• Tectonic hazard in Japan

  • 9.0 magnitude earthquake in Tohoku region in 2011
• Effects of Japan earthquake

  • Around 16,000 people died, 6,000 injured, 1.2 million homes destroyed, Fukushima nuclear plant severely damaged, roads and bridges destroyed
• Secondary effects in Japan

  • Powerful tsunami, Fukushima explosions released radioactive material, landslides blocked transport routes, 500,000 made homeless
• Tectonic hazard in Haiti

  • 7.0 magnitude earthquake near Port-au-Prince in 2010
• Effects of Haiti earthquake

  • 250,000-316,000 people died, 300,000 injured, 70% of buildings in Port-au-Prince destroyed, main infrastructure damaged
• Secondary effects in Haiti


  • Cholera epidemic killed 7,000, 4,000 prisoners escaped, lawlessness and looting increased, 1 in 5 jobs lost
• Japan's immediate response


  • Tsunami warning issued, Japanese Red Cross provided aid, trains stopped, 20km exclusion zone around Fukushima, but emergency response overwhelmed
• Japan's long-term response


  • 100% of buildings inspected and repaired, roads and airports reopened, electricity and water supply restored, new sea walls built
• Haiti's response


  • Slow, took 2-3 days for help to arrive, local people used bare hands to dig out rubble, almost 1 million in aid camps, 4.3 million provided food rations, bodies bulldozed into mass graves
• Haiti's long-term response


  • Reliant on other countries for $13 billion in aid, 1 million still homeless after 1 year, cash-for-work programmes set up, World Bank cancelled half of Haiti's debt
• Many people live in areas at risk from tectonic hazards, either by choice or necessity
• Reasons people live in hazardous areas


  • Can't afford to move, confident government will support them, volcanic soil is fertile for farming, volcanoes attract tourists
• Monitoring tectonic hazards

  • Earthquakes - seismometers and lasers monitor earth movements

  Volcanoes - monitor earthquakes, gas release, shape changes to predict eruptions
• Predicting tectonic hazards

  • Earthquakes - can forecast where they may occur by monitoring plate movements

  Volcanoes - can be predicted by close monitoring
• Protecting against tectonic hazards

  • Earthquakes - new buildings use reinforced concrete, existing buildings/bridges strengthened, automatic shut-off switches

  Volcanoes - buildings strengthened against ash, trenches/barriers to divert lava (with limited success)
• Planning for tectonic hazards

  • Avoid high-risk areas for new developments, emergency services prepare, educate people, plan evacuation routes, stockpile emergency supplies