Natural Hazards

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What are Natural Hazards

  • An extreme natural event or process that causes loss of life and/or extreme damage to property and creates severe disruption to human activities. 
  • Tectonic Hazards-These are natural hazards caused by the movement of tectonic plates e.g. volcanoes and earthquakes
  • Climatic Hazards-These are caused by the weather, they include tropical storms and drought.
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Constructive/Divergent Boundaries

  • When plates MOVE APART.
  • When the crust is pulled apart, it typically breaks along parallel faults that tilt slightly outward from each other.
  • As the plates separate, the block between the fault cracks and drops down in to the mantle.
  • The sinking of the block causes a rift.
  • Magma seeps upward to fill the cracks. New crust is formed along the boundaries.

EXAMPLE:  EURASIAN plate and the NORTH AMERICAN plate are moving apart at the mid Atlantic Ridge.


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Destructive Boundaries

  • Where two plates COLLIDE with each other.
  • Oceanic plate collides with a CONTINENTAL plate, the OCEANIC plate is forced downwards into the mantle forming a SUBDUCTION zone.
  • This forms a DEEP TRENCH, the edge of the continental plate is folded upwards into a mountain range. Repeated folding will cause plates to break and slip causing earthquakes.

EXAMPLE: Oceanic NAZCA plate crashing with continent of SOUTH AMERICA. Crash formed the ANDES mountains, the long strings of volcanoes along the mountain crest, and the deep trench off the coast of PACIFIC OCEAN


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Conservative/Transform Boundaries

  • Plates SLIDE PAST each other, or are moving in the SAME DIRECTION.
  • They dont slide past each other smoothly, often get stuck. PRESSURE builds up until suddenly the plates jump forward, sending out a shock of WAVES that cause an Earthquake.

EXAMPLE: SAN ANDREAS Fault. The area of California to the WEST of the fault is slowly moving north relative to the rest of CALIFORNIA


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1) EVAPORATION for the surface of the ocean, because of the usually HIGH ocean TEMPERATURES of 27 degrees.

2) Fast-rising, warm, moist air rises creating an area of very low pressure-the EYE OF THE STORM-which sucks air in. 

3) The ROTATING WINDS cause LOW pressure close to the EQAUTOR and absorb the moisture from the oceans, creating hurricanes.


  • Sea temp must exceed 27 degrees, 60m deep.
  • Time of year-May to November in the Northern Hemisphere, November to April in the southern Hemisphere.
  • Typical size 700km in diameter and can exceed 13km in height.
  • Areas of the world-Carribean, Central America, South East Asia, indian subcontinents. 
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Primary Effects of Hurricanes

  • Buildings and bridges are destroyed.
  • Rivers and coastal areas flood.
  • People drown, or are injured by debris.
  • Infastructure damaged.
  • Crops are damaged and livestock is killed.
  • Heavy rain causes landslides.
  • Beaches are eroded and coastal habitats damaged.
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Secondary Effects of Hurricanes

  • People are left homeless
  • Shortage of clean water and a lack of proper sanitation-making it easier for diseases to spread.
  • Roads are blocked or destroyed making it difficult for aid to get through.
  • Businnesses are destroyed causing unemployment.
  • Shortage of food because crops and livestock are short.
  • People may suffer psychological problems from traumor. 
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Human Causes of Drought

  • Overgrazing reduces vegetation in an area. Makes soil erosion caused by drought even worse-with fewer plants, the soil isnt held together as strongly making erosion easier.
  • Excessive irrigation- Irrigation is where water is artifically supplied from rivers or lakes to farmland to increase crop production,
  • Excessive irrigation depletes rivers and lakes, increases impact of drought when there is no water.
  • When irrigation water evaporates, salts are left in soil-SALTATION. Crops dont grow as well. 
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  • Drought occurs when there is less than normal rainfall over a set period of time also when evaporation is higher than precipitation. 


  • Vegetation dies
  • People and animals die from dehydration
  • Aquatic animals die when lakes and rivers dry up
  • Soil dries out and is easily eroded by wind. 


  • Animals die from starvation due to lack of vegetation
  • Shortage of food (no crops) and water
  • Conflict over food and water supplies.
  • Farms close causing unemployment
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