Geography - Restless Earth

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  • Created by: Harry
  • Created on: 14-04-14 11:41

With reference to a case study explain a destructi

Use Mount Saint Helense: Between 1857 - 1980 -> Infrequent in eruption

1) Heat arises from earth's core

 2) Convection currents occur in the mantle

3) Crust breaks up

5) The oceanic plate subducts and melts in subduction zone

6) Low silica magma (runny magma) rises through the S.American continent (is squeezed     up -> denser below)

7) Gains silica from continental crust 

8) Becomes thicker magma (high in silica) -> plugs and solidifies

9) Magma builds in a chamber -> creates pressure

10) Eventually results with explosive eruption

Referencing to Mt. St. Helens -> .Magma bakes rock -> produces ash

                                                   .Pyroclastic flow occurs -> .At 600 degrees: ash dust,                                                                                                  rocks and pices of lava at 80mph.

Pyroclastic flow travelled 30 miles north

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What are composite cone volcanoes?

Volcanoes that are steeper than the regular volcano, less frequent in eruption and are more explosive.


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What are constructive plate margins?

Eg -> Mid-atlantic ridge 

1) Convection currents in the mantle move in opposite directions

2) Oceanic crust pulls away from one another

3) Cracks and fractures form between the plates -> no solid crust

4) Magma forces its way into cracks (produces BASALT LAVA -> runny & low in silica) &     to the surface to form volcanoes


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Suggest and explain volcanic hazards

1) Lava flow

2) Volcanic ash . asphyxation

                        . drown

3) Pyroclastic flow .80mph

                            . 600 degrees

                            . Dense mixture of ash, gas and rock

4) Volcanic bombs

5) Lahar -> Volcanic mudflow

6) Flooding -> Rivers become dirty

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What are super volcanoes and their impacts?

'A mega colossal volcano that erupts at least 1000km3 of material'


1) Likely to destroy 10,000km2 of land

2) Would kill 87,000 people

3) 15cm of ash would cover buildings

4) Block out sunlight -> Would create a 'nuclear winter'

5) Would produce SO2 gas -> Poisonous

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What are the two types of eruption?

RED eruption: Occurs on a CONSTRUCTIVE plate margin (basaltic lava = runny lava, not as viscous)

GREY eruption: Occurs on a DESTRUCTIVE plate margin (acidic lava = viscous, plugs, pressurises and is explosive)


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How would we monitor & predict volcanoes?


  • Literally a pencil on a revolving drum
  • Looks for earthquakes -> one of the factors of possible future eruptions
  • Looks for increases in magnitude which could suggest an eruption

Tilt metres

  • Detects changes in the ground
  • E.g. :  a bulge at Mt. St. Helens could suggest gases & magma rising

Spider robot

  • A camera that monitors gases such as CO2, SO2 and H2S

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How would we monitor earthquake magnitude?


  • 1-12 descriptors
  • Earthquake magnitude measured by the effects
  • Simple -> no equipment needed
  • Con: Not very scientific -> Effects will vary on the country, building structure, etc.

            RICHTER SCALE

  • Scientific
  • Con: Needs equipment
  • Actually gets a value
  • Is LOGARHYTHMIC: if you go up by one, you go up by ten (e.g. 8-->9) 
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Why is the earth's crust unstable?

  • It is very thin
  • It is broken up into plates because of movement of the mantle below
  • It consists of two types: Oceanic & Continental


  • Is thin (6-10km thick)
  • Denser -> 3.0g/cm3
  • Newer -> 200 mil years
  • Constantly recycled: made and destroyed
  • Low in silica (40%)


  • Is thick (30-70km thick)
  • 2.6g/cm3 -> Not as dense
  • Older: up to 3 bil years old
  • Stable
  • More silia (70%)
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