tectonic hazards 🌋

• the earth’s crust is divided into slabs called tectonic plates that float on the mantle
• there are 2 types of crust: continental and oceanic
• continental crust is thicker (30-50km) and less dense
• oceanic crust is thinner (5-10km) and more dense
• tectonic plates move by slab pull ridge push
• the place where tectonic plates meet are called plate margins
• there are 3 main types of plate margin: destructive, constructive and conservative
• destructive plate margin: where 2 plates are moving towards one another
• destructive plate formation:

  1. an oceanic plate meets a continental plate
  2. the denser oceanic plate is subducted into the mantle and destroyed in the subduction zone
  3. volcanoes, earthquakes and oceanic trenches occur here
• destructive plate example:

  the oceanic nazca plate (west coast of south america) is being subducted beneath the continental south american plate
• constructive margin: where 2 plates are moving away from one another
• constructive plate margin formation:

  1. 2 plates move away from one another
  2. magma rises from the mantle to fill the gap
  3. new crust is created, often forming volcanoes (earthquakes also happen here)
• constructive margin example: the eurasian and north american plates are moving away from one another, forming the mid atlantic ridge
• conservative margins: when 2 plates are moving sideways past each other OR in the same direction at different speeds - no crust is created or destroyed but it does cause earthquakes
• conservative margin example: the pacific plate is moving in the same direction as the north american plate, but faster (at the san andreas fault)
• when volcanoes erupt they emit lava and gas, and some emit lots of ash
• ash emitted in volcanic eruptions can:

  • cover land
  • block out the sun
  • cause pyroclastic flows
• pyroclastic flows: heated currents of gas, ash and rock
• earthquakes at destructive margins happen when tension builds as oceanic plates get stuck as they’re subducted
• earthquakes at constructive margins happen when tension builds along cracks in the plates as they move away from one another
• earthquakes at conservative margins happen when tension builds up as plates get stuck moving past one another
• formation of earthquake:

  • plates move past one another, sending out shock waves (the earthquake)
  • shock waves spread out from the focus (they are stronger near the epicentre)
• epicentre: the point on the earth’s surface directly above the focus
• earthquakes are measured by the richter scale in magnitude
• earthquakes of magnitude 7 or above can cause major damage and deaths
• why people chose to live near places at risk from tectonic hazards:

  • family live there
  • they have a job there
  • its a wealthier country so there are monitoring and evacuation plans in place
  • soil there is fertile due to volcanic ash, so its ideal for farming
  • volcanoes are tourist attractions so many people around them work in tourism
• there are 4 different tectonic hazard management strategies: monitoring, prediction, planning and protection
• monitoring for earthquakes:

  • seismometers monitor earth‘s movements and can be used in early warning systems to give small warnings before large earthquakes
• monitoring for volcanic eruptions:

  • scientists can monitor the tell-tale signs of an eruption eg. escaping gas + changes in the shape of the volcano
• prediction for earthquakes:

  • they can’t be predicted reliably but forecasting where they might occur based off tectonic plate movement is possible
• prediction for volcanic eruptions:

  • can be predicted via close monitoring of the volcano
• protection for earthquakes:

  • new buildings use reinforced concrete that absorb earthquake energy
  • existing buildings can be strengthened with steel frames so they’re less likely to collapse
  • automatic shut-off switches can turn off gas + electricity to prevent fires
• protection for volcanic eruptions:

  • buildings can be strengthened so they’re less likely to collapse under the weight of ash
  • trenches and barriers can be used to try and divert lava away from settlements (although this is rarely successful)
• planning:

  • future developments avoid high risk areas
  • emergency services prepare eg. practising rescuing people from collapsed buildings
  • people can be educated so they know what to do in the event of a tectonic hazard
  • governments can plan evacuation routes
  • emergency supplies can be stockpiled eg. blankets, clean water, food