Tectonic Plates

Plate Margins and collision zones

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Plate Margins

Constructive (tensional) - Plates move apart

Destructive (collision boundary) - Plates move towards each other (Fold mountains)

Conservative - Plates slide past each other

Collision Margins - Continental plates pushing towards each other. Same density, cannot sink, so squeeze upwards making fold mountains.e.g Himalayas

Pressure - Earthquakes occur

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Constructive Boundary

Plates move apart - Found undea sea e.g Mid-Atlantic Ridge


  • Magma rises from mantle, magma erupts to surface of Earth
  • It cools + solidifies - Igneous Rock
  • Eventually rock builds - Volcano

Chains of underwater volcanoes have formed along plate boundary. One may erupt out of sea to form a volcanic island e.g. Surtey and Westman Islands near Iceland

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Destructive Plate Boundary

Move towards each other. Continental plate and oceanic plate. Oceanic is denser than Continental.

Oceanic plate melts due to friction + heat from mantle. Oceanic plate is forced underneath the continental - Subduction Zone

Earthquakes are triggered. Magma collects to form magma chamber, rised through cracks in contintental crust. 

Plates push together, Continental crush is squashed together, forced upwards. Fold mountains.

Nazca Plate (Oceanic) ------> South American Plate (Continental Crust)

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Conservative Margins

Move past each other (slide past)

No volcanoes but friction between two plates ----> EARTHQUAKES

Example - San Andreas Fault in California (Between North American Plate and Pacific Plate)


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Collision Margins

2 Continental Plates pushing towards into each other.

Same Density > cannot sink > squeeze upwards > fold mountains

Himalayas! Strong earthquakes at these margins due to pressure caused by two plates crashing into each other.


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Case Studies

Destructive Margin (Volcanoes + Earthquakes + Fold Mountains)  - Kobe Earthquake, Eruption of Mount Pinatubo

Conservative Margin (Earthquakes)  - California Earthquake

Collision Margin (Fold Mountains)  - Construction of the Himalayan Montains

Constructive Margin (Volcanoes and earthquakes) - Formation of iceland



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Examples of plate margins

Destructive - Nazca Plate + South American Plate

Constructive - Eurasian Plate + North American Plate

Conservative - Pacific Plate + North American Plate

Volcanoes are found at plate boundaries, in narrow belts. Ring of Fire around the Pacific Ocean


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Map Of Plate Margins


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Ocean Trenches

Formed at a Subduction Zone (Oceanic + Continental.)

Deep V shaped Trench parallel to the coast line of Nazca and South American Plate.


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Fold Mountains

Formed at both Subduction and Collision Zone.


Rivers deposite huge quantities of sediments in depressions called geosynclines

Millions of years, sediments compress to sedimentary rocks (Sandstone/Limestone)

Plates move together forcing sedimentary rocks upwards into a series of folds.

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Why People live on Fold Mts

Use landforms as a resource and adapt to the conditions within them.

Himalayas - Nepal, Asia

Alps - France Austria Switzerland Italy Europe

(http://www.geographicguide.net/earth/pictures/himalayas-asia.jpg) Himalayas

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Living in Himalayas

  • 80% are farmers in Nepal
  • Mining - Gold, diamonds. Copper ore + Slate > Pollutes environment
  • Tourism - treking/climbing/temples > money
  • Living with danger - Prepared, homes built with light roofs
  • Farmiing - few crops, rice & veg.


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Human activity surrounding fold mountains

  • Winter Sports > Skiing in resorts > Chamonix
  • Climbing and Hiking in Summer
  • Summer Lakeside Holidays
  • Agriculture - south facing slopes (Ubac Slope)
  • Forestry - coniferous forests for fuel and building.
  • Communications - Roads + Railways follow valleys
  • Hydroelectric power - steep slopes and glacial melt water are ideal for generating HEP - fast flowing rivers.
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Composite and Shield Volcanoes


  • Eruptions infrequent but often Violent                    
  • Steep-sided Volcano
  • Made of a variaty of materials
  • Destructive Plate Margins


  • Eruptions frequent and non-violent
  • Broad volcano
  • Made up of mostly lava
  • Constructive Plate Margin
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Named Example of Volcano

Montserrat- Caribbean Island

Island before:

  • Fertile/exotic
  • Tropical
  • Lively

Island After:

  • Dull/lifeless
  • Ruined
  • Deserted towns 23 people killed

Never erupted for 370 years

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Mt St Helens

Plates - North American + Pacific Plate

Date of Eruption - May 18th 1980

Facts - Triggered by 5.1 earthquake. Largest landslide speeds of 70-150 mph

Details - 57 people killed or never found. Mudflows destroyed 27 bridges, 200 homes, 185 miles of roadway,15 miles of railway, and wildlife + trees.


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