Natural hazards

• Natural hazards


  Sudden, severe natural events that threaten people or have the potential to cause damage, destruction & death, making the natural environment difficult to manage
• Natural hazards


  • They disrupt life causing social & economic impacts
  • 3 categories: atmospheric, geological, flooding
• Hazard risk


  Chance of a natural hazard occurring & being affected
• Risk affected by urbanisation, poverty, farming & climate change
• Hazard examples


  • Earthquakes
  • Volcanoes
  • Tsunamis
  • Avalanches
  • Landslides
• Layers of the earth


  • Inner core
  • Outer core
  • Mantle
  • Crust
• Inner core


  Centre & hottest part of the earth, solid iron & nickel, up to 5,500°C
• Outer core


  Layer surrounding inner core, liquid iron & nickel
• Mantle


  Thickest section ≈2,900km, semi-molten rock (magma), contains convection currents that move plates
• Crust


  Outer layer, 0-60km thick, solid rock we live on, split into plates
• Earthquake


  Sudden violent period of ground shaking, usually at margins of slow moving tectonic plates, friction & sticking between plates create enormous pressures & stresses which build to breaking point leading to earthquakes
• Focus


  Point of origin
• Epicentre


  Point on surface above focus
• Seismic waves


  Energy waves that travel out from the focus
• Strength of earthquakes


  Measured on seismometer with the Richter or moment magnitude scales
• Volcanoes


  Large often cone-shaped landforms formed by eruptions of magma from within the mantle
• Most volcanoes occur on plate margins (Pacific ring of fire, Mid-Atlantic ridge), some occur at hot spots (crust thin enough for magma to break through, Hawaii)
• Convection currents


  Radioactive decay in core generates high heat, lower parts of magma heat up, become less dense and rise, as they move to the top they cool down, become more dense and sink, circular movements form convection currents, create drag on plates and cause movement
• Tectonic plates


  Crust split into 7 major & several minor plates, 2 types of crust- oceanic (dense, thin) & continental (less dense, thicker), plates move driven by convection currents in the mantle & under gravity
• Plate margins


  • Constructive (divergent) (Iceland)
  • Destructive(convergent)(Chile)
  • Collisional(Nepal/Himalayas)
  • Conservative (San Francisco)
• Constructive (divergent) plate margin


  2 plates move apart, magma rises to the surface, causes mild earthquakes, lava flows far before cooling creating flat shield volcanoes
• Destructive(convergent) plate margin


  An oceanic & continental plate move towards each other, dense oceanic plate subducted, friction causes earthquakes, sticky gas rich magma, steep sided composite volcanoes with violent eruptions formed
• Collisional plate margin


  2 continental plates, same density so no subduction or magma for volcanoes, crust crumples & lifts to form fold mountains, powerful volcanoes
• Conservative plate margin


  2 plates move past each other, friction builds stresses that trigger earthquakes when they slip, no volcanoes
• Chile earthquake - 27/2/10, 8.8 magnitude, shallow focus, just off the coast, destructive margin, 3.34am, 3 mins
• Nepal earthquake - 25/4/15, 7.9 magnitude, very shallow focus (15km), 60km NW Kathmandu, collision margin, 11.26am
• Effects of earthquakes


  • Vary based on size, level of development, depth of focus, distance from epicentre, population density, time of day
• Primary effects of earthquakes

  • Caused by ground shaking
  • Chile - 500 killed, 12,000 injured, 800,000 affected, significant destruction of buildings, power, water & communications cut, $30 billion damage
  • Nepal - 9,000 killed, 20,000 injured, 8,000,000 affected, widespread destruction of buildings, power, water, sanitation & communications cut, $5 billion damage
• Secondary effects of earthquakes


  • Result of shaking
  • Chile - communities cut off by landslides, costal towns devastated by tsunami, chemical plant fire forced evacuations
  • Nepal - communities cut off by landslides & avalanches, at least 19 killed on Everest due to avalanches, flooding in blocked rivers
• Immediate responses to earthquakes


  • Chile - swift & effective emergency service response, key roads repaired in 24 hours, most power & water within 10 days, $60 million national appeal built 30,000 emergency wooden shelters
  • Nepal - overseas aid from NGOs, helicopter search & rescue, supply drops in remote areas, 30,000 migrated from Kathmandu for shelter & family & friend's support
• Long-term responses to earthquakes


  • Chile - strong economy meant reduced need for aid, government reconstruction plan for 200,000 hoses, full recovery in 4 years
  • Nepal - roads repaired, landslides cleared, flood lakes drained, international conferences for technical & financial support, Indian border blockade caused fuel, medicine & material shortage
• Reasons for living at risk from natural hazards


  Poor people have no choice, earthquakes & eruptions rare so not a great threat, earthquake resistant building designs reduce risk, effective monitoring gives warnings for evacuation, margins coincide with favourable areas, no experience or knowledge of risk, volcanoes give fertile soil, rich mineral deposits & hot water, fault lines can allow water to reach the surface in arid regions
• Iceland - eruptions every 5 years on average, low risk due to awareness & monitoring, volcanic rocks used in road & building construction, natural hot water for water & central heating for 90% of all buildings, landscapes bring tourists, geothermal energy 25% of all
• Monitoring natural hazards


  • Volcanoes - remote sensing, seismicity, ground deformation
  • Earthquakes - microquakes, bulging of the ground, raised groundwater levels
• Predicting volcanoes


  Monitoring allows accurate prediction & effective evacuation
• Predicting earthquakes


  Accurate prediction impossible as no clear warning signs, historical records can determine probability & help plan
• Protecting against natural hazards


  • Volcanoes - earth embankments & explosives used to successfully divert lava flows
  • Earthquakes - drills keep people prepared, earthquake resistant construction best way
• Planning for natural hazards


  • Volcanoes - risk assessment & hazard mapping identify areas to practice evacuation or restrict building
  • Earthquakes - risk assessment & hazard mapping to identify areas to protect buildings & infrastructure
• Global atmospheric circulation model

  Worldwide system of winds transporting heat from tropical to polar latitudes, made up of 6 cells with 3 either side of the equator
• Hadley, Ferrel & Polar cells


  Outwards from the equator, warm air=low pressure=rising, Cold air=high pressure=sinking, surface winds move from low to high pressure transferring heat & moisture