global hazards

• la niña

  • normal conditions become more extreme
  • trade winds blow to the west more strongly and more cold water rises in the eastern pacific
  • causes heavy rainfall in west
  • causes less rainfall in the east
  • occurs every 2-7 years
• el niño

  • pressure rises in the western pacific and fall in the east
  • causes trade winds (normally blown from east to west) to weaken or reverse direction
  • causes less rainfall in the west (australia)
  • causes more rainfall in the east (peru)
  • occurs every 3-4 years and lasts for 9-12 months
• tropical storm formation

  1. oceans surface water reaches at least 27°C, the warm air above the water rises quickly, causing an area of very low pressure
  2. as the air rises quickly more warm moist air is drawn upwards from above the ocean creating strong winds
  3. the rising warm air spirals upwards and cools. the water vapour condenses and forms cumulonimbus clouds
  4. these clouds form the eye wall of the storm
• global atmospheric circulation

  
• low pressure (depression)

  rain + storms

  • due to hot air rising from land
• high pressure

  clear skies

  • due to air warming as it sinks as this acts to suppress any showers or storms
• composite volcanoes

  • occurs at destructive plate boundaries
  • subducted oceanic crust contains lots of water. the water can cause the subducted crust to erupt
  • eruption start with ashy explosions then a layer of thick, sticky lava that can’t flow far. forming a steep sided cone
• shield volcanoes

  • occurs at hotspots or constructive plate boundaries
  • not very explosive and only lava
  • lava is runny, flows quickly and spreads over a large area forming a low gentle sided volcano
• convection currents

  lower parts of mantle are sometimes hotter than the upper parts. when these lower parts heat up they become less dense and slowly rise. as they move towards the top, they cool down and become more dense causing them to sink
• collision plate boundary

  1. convection current causes two continental plates to move towards each other
  2. the plates are forced upwards as they collide
  3. large earthquakes are caused as these plates collide
  4. fold mountains are created at this boundary
• constructive plate boundary

  1. convection currents cause two plates to move away from each other
  2. a gap is created between plates
  3. magma rises into the gap from the mantle
  4. this repeats and a volcano is created at the gap between the plates
• destructive plate boundary

  1. convection currents cause two plates to move toward each other
  2. the denser (oceanic) crust subducts below the continental
  3. as it sinks it rubs against the continental plate causing an earthquake and melting the crust
  4. melted magma rises causing a vocano
• conservative plate boundary

  1. convection current causes two plates to move sideways past each other
  2. plates get locked together and pressure builds up
  3. eventually, two plates slip free and release stored energy
  4. this causes a huge earthquake