World at Risk 2

World at Risk 2

1. Hazard distribution

2. Geophysical hazards usually occur near plate boundaries

   • Earths crust made up of huge plates called tectonics
   • Two types
     • thicker (less dense) is the continental crust
     • Thinner (more dense) is the oceanic crust
   • Plates move because of convection currents in the mantle these are caused by temperature differences within the mantle

3. Volcanoes and earthquakes occur at constructive boundaries

   • Constructive- 2 plates move apart
   • Mantle is under pressure from plates above
   • when they move pressure is released this causes mantle to melt and produce magma
   • Magma is less dense than the plate above so it rises and erupts

4. Volcanoes and earthquakes also occur at destructive boundaries

   • Destructive- when 2 plates move towards each other
   • Continental and oceanic crust move towards each other more dense oceanic is forced under the continental plate.
   • Oceanic is heated b friction and contact with the upper mantle which melts the magma
   • magma is less dense than the continental crust and will rise back to the surface to form a volcano

5. Earthquakes also occur at conservative boundaries

   • conservative- when 2 plates are moving apart
   • 2 plates get locked together in places and pressure builds up
   • Causes plates to jerk past each other releasing the energy as an earthquake

6. Tropical cyclones occur over warm water

   • develop above water 26.5C or higher Moist air rises and condenses it releases energy which increases wind speed
   • loses strength when over land because energy supply is cut off
   • occur between 5 and 30 north and south of the equator
   • Cyclones spin because of the Coriolis effect force that deflects the path of winds due to the earths rotation
     • This is why they move away from the equator

7. Volcanoes also occur away from plate boundaries

   • These volcanoes are thought to be caused by magma rising from large chamber beneath the crust