Mount St Helens

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  • Created by: Jiya
  • Created on: 10-01-16 11:07


·         Composite Volcano in Washington State, US

·         On destructive plate boundary with Juan de Fuca plate being subducted, Pacific Ring of fire

·         18th May 1980, 8:32 am

·         Pressure in crust formed 450 foot bulge in 2 months which exploded after 5.1 Richter earthquake

·         First sign of eruption was ash and steam eruptions from crater

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Primary Impacts

·         Main explosion felled trees up to 24km away

o    Known as blowdown

·         Landslide allowed vent to explode sideways causing pyroclastic flow

·         Pyroclastic flow moved at over 100kph destroying all life in its path

·         Ash deposited 1cm deep over 120km away

·         Ash took 2 weeks to travel the world

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Secondary Impacts

·         Landslide caused mudflow

·         Most destructive in US history, changed the landscape forever

·         Port of Portland lost $3million per month in lost trade when Columbia shipping canal closed

·         Increased tourism

o    3 million tourists each year

·         Soil fertility improved due to ash deposits

·         Monitored constantly by USGS and plans made for future eruptions

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Immediate Response

·         Evacuation of local residents

·         Information given out on News Channels

·         National Guard used helicopters to look for victims and survivors, rescued 189 people

·         Masks provided by Authorities

o    2 million to prevent respiratory diseases

·         Roads cleared of ash

·         Shelter found for stranded tourists and those made homeless

·         $951 million pledged by congress for disaster relief, most of which went to Small Business Administration

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Secondary Response

·         USGS set up monitoring of volcano

·         President Raagan set aside 100,000 acres around volcano to be Mount St Helens Monument Site

o    Picnic sites, campsites, nature trails etc

·         $70 million in compensation to farmers for loss of crops

·         650,000 tonnes of ash cleared

o    Cost $2.2 million

o    Took 10 weeks

·         10 million trees replanted as there was a huge loss in timber

·         Drainage tunnels cleared and channels dredged of excess material

·         New highway built costing $7 million to replace damaged roads

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