AQA A2 Geography

Volcanic eruption in MEDC - Mt St Helens

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  • Created by: JamesMck
  • Created on: 04-06-14 09:51

Location and nature of hazard

  • In the Cascade mountains
  • A composite cone volcano with andesitic lava
  • Destructive plate boundary - Juan de Fuca subducting under the North American plate
  • March 1980 - series of small earthquakes and a bulge appeared 
  • May 18th 1980, 5.1 magnitude earthquake followed by an eruption of volcanic material (rock, ash, steam and hot gases). 
  • Eruption was 5 out of potential 8 on Volcanic Explosivity Index.
  • The lateral blast covered an area of 600 km2 north of the volcano
  • Primary hazards: pyroclastic flows (covered 230 sqaure miles, travelling at 300 mph and 350 degrees Celcius), volcanic bombs (travelling up to 8 miles from volcano), a huge landslide (covered 23 sqaure miles, travelling at speeds up to 150 mph), smoke and gases released (up to 10 miles high)
  • Secondary hazards: lahars (travelling up to 60 mph got into the Toutle and Cowlitz rivers therefore travelled many miles, destroying 35 bridges)
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Social Impacts

  • 57 killed directly
  • Caused plane crash and traffic accident leading to 7 more deaths indirectly
  • 250 homes destroyed 
  • Unemployment rose tenfold
  • Social facilities were lossed (impossible to fish in Spirit Lake filled with toxic gases)
  • Telephone lines and electricity supplies were knocked out
  • 185 miles of highway and 15 miles of railway destroyed, making transport nearly impossible
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Economic Impacts

  • Total cost at $1.1 billion
  • $2.2 million spent clearing up ush in US City Yakima
  • Timber industry brought to hault as 4 billion trees destroyed 
  • Airport shut for 2 weeks and 1000 flights cancelled - adverse affect on tourism income
  • Tourists no longer visited the area through fear of safety causing negative multiplier in local economy (however this only proved to be short term, eventually tourism soared again as people were intrigued to see the volcano)
  • Ash clogged up car engines and farm machinery with total cost to farmers estimated at $100 million.
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Environmental Impacts

  • 4 billion trees flattened, enougth timber to make 300,000 2-bed houses
  • 7000 big game animals died (e.g. elks) - affected food chains and diversity
  • Out of 32 small animal species, only 14 are known to have survived.
  • Sediment in Spirit Lake rose by 90 metres.
  • Over 250km of river ecosystem destroyed by lahars - killing all fish
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  • Exclusion set up from middle of March with red zones of no activity allowed and blue zones of certain acitivies being allowed (essential farming and forestry work)
  • Evacuation of 2000 people from area
  • There was a lot of public opposition to the exclusion area with people constantly trying to get round road blocks to get closer to volcano
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Immediate Response

  • National Guard flew helicopter rescue missions into the blast zone for 2 weeks and rescued 130 people
  • National Guard also issued clean water, emergency food rations and medical supplies.
  • 2 million as masks sent from government to prevent respiratory problems
  • Yakima took 3 days to clear ash
  • Temporary rescue centres created for those made homeless
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Long Term Response

  • The Toutle, Cowlitz and Columbia Rivers had to be dredged
  • Over 10 million trees replanted
  • Bridges were rebuilt with a wider span in attempt to avoid blockages from future lahars
  • The volcano is now monitored constantly by USGS and clear plans have been made to prepare and warn people in the area beyond the immediate blast zone to make them aware of the risks of the ash clouds.
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