11.2.1

Volcanoes & Their Products

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Volcanic Eruptions

When a volcano erupts at the Earth's surface, it can produce lots of different things, including:

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Lava

  • Lava is magma (molten rock) above the surface of the Earth.
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Gases

  • Volcanoes emit lots of gases like sulfur.
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Ash

  • Ash is tiny pieces of burnt rock fragments that are blown into the atmosphere, usually at some force.
  • These pieces fall on land and can float in the air, causing a volcanic winter (by blocking out the sun).
  • A volcanic winter describes when a volcano erupts, producing lots of ash, which then blocks the sun. Mount Pinatubo's 1991 eruption reduced global temperatures for 3 years.
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Pyroclastic flows

  • Pyroclastic flows are currents of hot ash, lava and gas that can move downhill at speeds of up to 500km/h during an eruption.
  • Pyroclastic flows are impossible to outrun.
  • They can reach temperatures of up to 1000oC and can cover distances of up to 30km from the volcano.
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Types of Volcano

The 2 main types of volcano are shield volcanoes and composite volcanoes.

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Shield volcanoes

  • Found at divergent tectonic plate margins or hotspots (like in the Pacific).
  • Not particularly explosive.
  • They release 'basaltic lava' when the volcano erupts. Basaltic lava is like a liquid that flows gradually, creating a volcano with a gentle gradient (rather than a steep slope).
  • Shield volcanoes do not produce any ash.
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Composite volcanoes

  • Found at convergent tectonic plate boundaries.
  • Erupt explosively.
  • Instead of basaltic lava, composite volcanoes erupt andesitic lava.
    • Andesitic lava is thicker than basaltic lava because it has more silica in it.
    • Because andesitic lava is thicker, it travels less far and composite volcanoes have steeper sides, forming a cone shape.
  • Mount Pinatubo, Mount Vesuvius in Italy and Mount Fuji in Japan are examples.

Jump to other topics

1Geography Skills

2Geology of the UK

3Geography of the World

4Development

5Weather & Climate

6The World of Work

7Natural Resources

8Rivers

9Coasts

10Glaciers

11Tectonics

12Climate Change

13Global Population & Inequality

14Urbanisation

15Ecosystems

16Life in an Emerging Country

17Analysis of Africa

18Analysis of India

19Analysis of the Middle East

20Analysis of Bangladesh

21Analysis of Russia

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