World at Risk - Hazard Distribution

This is taken from the CPG books

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  • Created by: keeels
  • Created on: 07-05-14 18:37
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  • Hazard Distribution
    • Plate Boundaries
      • The Earth's crust is made up of huge plates called tectonic plates that sit on top of the mantle
      • Plates are made up of two types of crust
        • The thicker (but less dense) crust is called continental crust - it's mostly above sea level
        • The thinner (but more dense) crust is called oceanic crust - it's mostly below sea level
      • The plates move because of convection currents in the mantle - the currents are caused by temperature differences within the mantle
      • Volcanoes and earthquakes most commonly occur at the boundaries where the plates meet
      • There are three types of plate boundary - Constructive, Destructive, and Conservative
    • Constructive Boundaries
      • A constructive boundary occurs where two plates are moving apart
      • The mantle is under pressure from the plates above. When they move apart, the pressure is released at the boundary
      • The release of pressure causes the mantle to melt, producing magma
      • The magma is less dense than the plate above, so it can rise and can erupt to form a volcano
      • For example, the Eurasian plate and North American plate are moving apart at the mid-Atlantic ridge. Iceland has been formed where magma has risen through the gap to form volcanoes
      • The plates don't move apart in a uniform way - some parts move faster than others. This causes pressure to build up. When the pressure becomes too much the plate cracks, making a fault line and causing an earthquake. Further earthquakes may also occur along the fault line once it's been created.
    • Destructive boundary
      • A destructive boundary occurs where two plates are moving towards each other
      • Where continental crust and oceanic crust are moving towards each other, the more dense oceanic crust is forced under the less dense continental crust (it's sub-ducted)
      • The oceanic crust is heated by friction and contact with the upper mantle, which melts it into magma
      • The magma is less dense than the continental crust above and will rise back to the surface to form volcomes
      • For example, the Pacific plate (oceanic crust) is subducting beneath the Eurasian plate (continental crust) at the Japan trench. The Japanese island arc has been formed where magma has risen through the crust to from volcanoes
      • The same process occurs where two plates of oceanic crust are moving towards each other - the denser of the two will be subducted, e.g this has been formed the volcanic islands of Indonesia
      • As one plate moves under the other they can get stuck. This causes pressure to build up. When pressure becomes too much the plates jerk past each other, causing an earthquake
      • Where two plates of continental crust are moving towards each other, neither is subducted so there aren't any volcanoes - but the pressure that builds up between them can cause earthquakes, e.g the Kashmir earthquake (2005)
    • Conservative boundary
      • A conservative boundary occurs where two plates are moving past each other
      • The two plates get locked together in places and pressure builds up. As with destructive boundaries, this causes the plates to jerk past each other (or to crack forming fault lines) releasing the energy as an earthquake,
      • For example, the Pacific plate is moving past the North American plate. Many earthquakes occur along this boundary and at its fault lines, e.g the San Andreas fault through California
    • Volcanoes can occur far away from any plate boundaries, e.g in Hawaii. These volcanoes are thought to be caused by magma rising from a large chamber beneath the crust. Areas like Hawaii are called Volcanic hotspots
    • Warm Water
      • Tropical cyclones are huge storms with strong winds and torrential rain
      • Tropical cyclones develop above sea water that's 26.5 degrees or higher. As warm, moist air rises and condenses, it releases energy which increases wind speed.
      • Tropical cyclones lose strength when they move over land because the energy supply from the warm water is cut off.
      • Most cyclones occur between 5 degrees and 30 degrees north and south of the equator - more 30 degrees away from the equator, the water isn't warm enough for cyclones to occur
      • Cyclones spin because of the Coriolis effect (the force that deflects the path of winds due to the Earth's rotation)
      • Cyclones don't occur 0-5 degrees either side of the equator because the Coriolis effect there isn't strong enough to make them spin
      • The Coriolis effect is also why they move away from the equator
      • They move westward due to the east-west winds in the tropics . For example, the trade winds move tropical cyclones westwards across the Atlantic Ocean towards the Caribbean Sea
      • Tropical cyclones are also known as hurricanes (when they occur in the Atlantic Ocean or Caribbean Sea) and typhoons (when they occur in the Pacific Ocean)


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