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:

Lava

Lava

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

Gases

  • Volcanoes emit lots of gases like sulfur.
Ash

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.
Pyroclastic flows

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.
  • Pyroclastic flows can reach temperatures of up to 1000oC and can cover distances of up to 30km from the volcano.
Diagram

Types of Volcano

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

Shield volcanoes

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.
Composite volcanoes

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.
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