Geography Exam week Volcanos

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  • Created by: pigs
  • Created on: 27-03-17 17:36

destructive boundaries

Destructive plate boundary

A destructive plate boundary is sometimes called a convergent or tensional plate margin. This occurs when oceanic and continental plates move together. The oceanic plate is forced under the lighter continental plate. Friction causes melting of the oceanic plate and may trigger earthquakes. Magma rises up through cracks and erupts onto the surface.

An example of a destructive plate boundary is where the Nazca plate is forced under the South American Plate.

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constructive boundaries

Constructive plate boundary

A constructive plate boundary, sometimes called a divergent plate margin, occurs when plates move apart. Volcanoes are formed as magma wells up to fill the gap, and eventually new crust is formed.

An example of a constructive plate boundary is the mid-Atlantic Ridge.

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conservative boundaries

Conservative plate boundary

A conservative plate boundary, sometimes called a transform plate margin, occurs where plates slide past each other in opposite directions, or in the same direction but at different speeds.

Friction is eventually overcome and the plates slip past in a sudden movement. The shockwaves created produce an earthquake.

This occurs at the San Andreas Fault in California.

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Volcanos

A volcano is an opening in the Earth’s crust. It allows hot magma, ash and gases to escape from below the surface

Magma chamber – large underground pool of magma

  • Lava – magma, once it reaches the surface

  • Crater – bowl-shaped basin in the top of the volcano

  • Vent – central tube which magma travels through

  • Secondary cones – eruptions from other vents may build up secondary cones on the flanks

  • Ash, steam and gas – material thrown out by the volcano

  • Volcanic bombs – larger material thrown out by the force of eruption

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Volcanos Part 2

Types of volcano

There are two types of volcano, composite and shield.

Composite volcanoes are steep-sided and cone-shaped, made up of layers of ash and lava and containing sticky lava which doesn’t flow very far.

Mount Etna in Italy is a composite volcano.

Shield volcanoes have gently sloping sides and runny lava that covers a wide area. Gases escape very easily from shield volcanoes.

Mauna Loa in Hawaii is a shield volcano.

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Volcano diagram

(http://www.bbc.co.uk/staticarchive/71ceb0b5bde6ad13b341c5684cdcb8ed1be10357.png)

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Destructive Plate boundary diagram

(http://www.bbc.co.uk/staticarchive/eee7117dc74a7dc9efbd2dd5eb9fa09e8bbb751a.png)

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Constructive boundary diagram

(http://www.bbc.co.uk/staticarchive/99674b272695d3a9b9afa83b291272b14ae61d4e.png)

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Conservative plate boundary diagram

(http://www.bbc.co.uk/staticarchive/859fd5a69269cc266396319515a05c9aacf9f41e.png)

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Key points

1. Constructive and destrucitve plate boundaries cause volcanos

2. Conservative boundaries cause earthquakes

3. Volcanos are openings in the Earth's crust

4.there are two types of volcano: shield and composite

5. boundaries are where two plates meet

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