Case Study - Volcano MEDC - Mt. St Helens

Mount St. Helens

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Mt. St Helens - What caused it.

Mt. St Helens

  • Mountain rumbling for 2 months, 5 mile exclusion zone around the volcano.
  • At 8:32am on May 18th 1980, rising magma a mile below the surface caused a landslide on the northern side of the volcano - which was massive, the largest recorded in history.
  • 8000 million tons of rock rushed down the mountain --> triggered simultaneous blast of steam, pumise + ash, with a temperature of 600 degrees to the north at 670mph.


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Mt. St Helens - The Effects

This unique lateral explosion caused:

  • No trees left standing within 6 miles of the blast
  • A cloud of ash 12 miles high
  • Generated heat that melted glaciers in the area
    • This produced floodwaters 60 feet high which travelled at up to 100 mph. Brought down many trees.
    • The force of it swept away bridges up to 40 miles away.


  • After the eruption, the mountain had lost approx. 1300 feet from its summit.
  • 540 million cubic metres of ash had been thrown into the atmosphere. (At times, this was sufficient to turn day into night 50 miles away!!)
  • By the end of the eruption, Mt. St Helens had claimed the lives of 57 people.


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