Mount St Helens, USA (MEDC case study)

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  • Created by: Kelleigh
  • Created on: 31-05-13 20:36

Background Information

The cascade mountains in North West USA

It erupted on 18th May 1980, 2 months previous volcanic activity, 5.1 on the richter scale

It was inactive for 123 years

It's a tourist destination

People lived near mt st Helens because of beautiful scenery (spirit lake), forestry, fertile soils, inertia (Harry Truman)

It's a strato volcano

power of 27,000 Hiroshima bombs

370miles sq in 4 minutes

57 lives

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Destructive plate margin, where the juan de fuca (oceanic plate) was being subducted under the North American plate (continental plate)

This lead to immense frictio, the melting of the oceanic plate, build up magma, increase in pressure and finally the resultant explosion

the eruption was large because the magma could not escape due to a (ice and rock)plug in the crater of the volcano.

Magma squeezed into a secondary fissure on the northern side creating a large bulge called a cryptodome

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Primary effects

filled spirit lake

the sky was choked with ash

10's of millions of trees were destroyed

all vegetation 21km to the north of the volcano was levelled

volcanic deposits up to 5 metres deep left on the hillside

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Secondary effects

Explosion heard 700 miles away

Tourism, crops, farming, fishing and logging industry crippled

media coverage was big

water temperatures raised in rivers and lakes, so fish were killed, salmon and trout

ash got into the engines in 3 US states

navigation was disrupted

fertile land in the future

different tourists, a tourist centre was established

influenced futute volcanology

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Immediate responses

20 mile exclusion zone (march 31st 1980)

geologists and volcanologists arrived to monitor progress

helicopters were mobilised

emergency centres were set up

many donations were given

roads were cleared for emergency veichles

imported gas masks

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Long term responses

Start of modern volcanology


rebuilding communications

replanting programmes

infrastructure rebuilt /repaired

advertising in order to bring back tourists

- in 1993 the tourist centre opened, it gets over 1 million visitors per year

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