Restless Earth

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The structure of the Earth

The Earth is made up of four concentric layers: 

  • Inner Core – This is in the centre of the earth, temperatures 4000-5000 degrees
  • Outer Core – This is a liquid layer also composed of Iron and Nickel and is extremely hot with temperatures similar to the inner core.
  • Mantle – This is the widest section of the Earth at approximately 2,900km. It s made up of semi-molten rock called magma. Towards the top of the mantle the rock is hard, but lower down nearer to the centre of the earth the rock is soft and beginning to melt.
  • Crust – This is the thin outer layer of the earth which is only between 0-60km thick. The crust is the solid rock layer which we live on. There are two different types:
    • Continental Crust – Carries land (30-50km thick)
    • Oceanic Crust – Carries water (5-10km)
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Distrubution of tectonic plates

  • The Earth's crust is broken up into pieces called plates.
  • Convection currents in the mantle caused by heat rising and falling generated by radioactive decay in the core, causes the plates to move.
  • The plate movements and the activity inside the earth is called plate tectonics.
  • Plate tectonics cause earthquakes and volcanoes which usually occur on plate boundaries.
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Plate Boundaries

Destructive - Where two plates collide and one plate flows beneath the other – subduction. - Earthquakes and volcanoes occur here - E.g.: Nazca Plate and South American Plate

Constructive - Rising convection currents pull crust apart forming volcanic ridge - Mid-Atlantic Ridge - E.g.: Eurasian and North American Plates

Conservative - Two plates slide past each other - Earthquakes occur here - E.g.: San Andreas Fault, California

Collision - Two continental plates collide and the two plates buckle - Many earthquakes occur here - E.g.: Indo-Australian and Eurasian plates

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Shield volcanoes

  • Are found on constructive plate boundaries
  • Are formed by eruptions of thin, runny lava which flows a long way before it solidifies
  • Have gentle sloping sides and a wide base
  • Contain basaltic magma which is very hot with low silica and gas content
  • Erupt frequently but not violently
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Composite volcanoes

  • Are found on destructive plate boundaries
  • Are formed by eruptions of viscous, sticky lava and ash that don’t flow far
  • Have steep sloping sides and a narrow base
  • Made up of layers of thick lava and ash
  • Contain andesitic magma which is less hot but contains lots of silica and gas
  • Erupt infrequently but violently, including pyroclastic flows (mix of ash, gases and rock)
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Haiti 2010 - LEDC

Primary Impacts

  • 316,000 people were killed and 1 million made homeless
  • 250,000 homes and 30,000 other buildings destroyed or badly damaged they had to be demolished
  • Transport and communication links were damaged
  • Hospitals (50+) and schools (1300+) were badly damaged
  • The main prison was destroyed
  • Presidential palace was destroyed
  • Roads blocked by rubble

Secondary Impacts

  • 1 in 5 people lost their jobs because so many buildings were destroyed
  • Hospitals became full very quickly
  • Diseases, especially cholera became a problem
  • People sleeping in streets for fear of more earthquakes.
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Haiti 2 years on

  • 80% of the rubble had been cleared
  • 350,000 people still living in tents
  • Only 111,000 out of the 125,000 shelters planned had been built
  • Not all the money promised in aid had been sent, making recovery difficult
  • There is a shortage of safe, clean water
  • Only 18% of the required homes had been built
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Predicting Hazards

The difficulties of predicting these hazards are that we don’t know…

  • When it will happen
  • Exactly where it will happen
  • How big it will be
  • What other impacts it may have
  • How many people live there
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Predicting Hazards

Because it is very hard to predict when an earthquake or volcano is going to happen, people need to be prepared for when one may occur. People can…

  • Create an exclusion zone around the volcano
  • Make sure they have an evacuation plan
  • Have an emergency supply of basic provisions such as food and water
  • Ensure that money is available to deal with the emergency
  • Ensure that a good communication system is in place
  • Do earthquake drills so they know what to do in the event of a real earthquake
  • Build earthquake proof buildings. In San Francisco, the Transamerica Pyramid was designed to absorb the energy of an earthquake and withstand the movement of the Earth
  • Build roads and bridges to withstand the power of an earthquake
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