World at Risk 2

Hazard distribution
Geophysical hazards usually occur near plate boundaries
1. Earths crust made up of huge plates called tectonics
2. Two types
  1. thicker (less dense) is the continental crust
  2. Thinner (more dense) is the oceanic crust
3. Plates move because of convection currents in the mantle these are caused by temperature differences within the mantle
Volcanoes and earthquakes occur at constructive boundaries
1. Constructive- 2 plates move apart
2. Mantle is under pressure from plates above
3. when they move pressure is released this causes mantle to melt and produce magma
4. Magma is less dense than the plate above so it rises and erupts
Volcanoes and earthquakes also occur at destructive boundaries
1. Destructive- when 2 plates move towards each other
2. Continental and oceanic crust move towards each other more dense oceanic is forced under the continental plate.
3. Oceanic is heated b friction and contact with the upper mantle which melts the magma
4. magma is less dense than the continental crust and will rise back to the surface to form a volcano
Earthquakes also occur at conservative boundaries
1. conservative- when 2 plates are moving apart
2. 2 plates get locked together in places and pressure builds up
3. Causes plates to jerk past each other releasing the energy as an earthquake
Tropical cyclones occur over warm water
1. develop above water 26.5C or higher Moist air rises and condenses it releases energy which increases wind speed
2. loses strength when over land because energy supply is cut off
3. occur between 5 and 30 north and south of the equator
4. Cyclones spin because of the Coriolis effect force that deflects the path of winds due to the earths rotation
  1. This is why they move away from the equator
Volcanoes also occur away from plate boundaries
1. These volcanoes are thought to be caused by magma rising from large chamber beneath the crust

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	Created by olw-1234 over 11 years ago