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Geography

Volcanoes and volcanic eruptions

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Case study: Mount St Helens 1980 (MEDC)

Map showing location of Mount St Helens

Map showing location of Mount St Helens

Mount St Helens is on the plate boundary between the Juan de Fuca plate and North American plate. When it erupted it permanently changed the surrounding landscape.

Effects of the eruption

Primary effectsSecondary effects

Nuée ardente [nuee ardente: A French phrase, literally meaning 'glowing cloud', which describes the cloud of volcanic debris formed by the collapse of a volcanic dome. ] (hot ash and gas) destroyed forests and logging camps.

63 people were killed, mainly by poisonous gases.

Lahars [lahar: A destructive volcanic landslide or mudflow, consisting of a mixture of volcanic debris, mud, rock and water. ] (mudflows of ash and water) covered an extensive area surrounding the volcano.

Ash blocked rivers destroying popular fishing sites and causing flooding. This in turn destroyed crops and livestock.

Flooding destroyed communications such as road and railway bridges.

Sediment carried downstream ruined barge transport on the Columbia River.

Short-term responses and results

  • Communications such as roads and bridges were repaired.
  • People were rehoused.

Long-term responses and results

  • Soil fertility improved due to the ash deposits.
  • The volcano is now more carefully monitored.
  • Tourism has increased, boosting the local economy.

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