Case study: Mount St Helens 1980 (MEDC)

Map of the St Helens volcano eruption and the movement of plates

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.

Primary effects

  • Nuée ardente (hot ash and gas) destroyed forests and logging camps.
  • 63 people were killed, mainly by poisonous gases.
  • Lahars (mudflows of ash and water) covered an extensive area surrounding the volcano.

Secondary effects

  • 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.