Case study: Mount St. Helens, USA (1980)

Where is Mount St. Helens located?

Washington, USA

When did Mount St. Helens erupt?

May 18th 1980

Why did Mount St. Helens erupt? What caused the eruption?

• the Juan de Fuca plate (oceanic crust) subducted underneath the North American plate (continental crust) into the mantle

• destructive oceanic-continental plate boundary

• magnitude 5 earthquake underneath the volcano at 8:32am

What were some primary effects of the eruption?

• 61 deaths

• every form of life within a 25km (17-mile) northwards blast zone range of the volcano was destroyed

• 370 square miles of surrounding area destroyed

• tens of millions of trees destroyed

• 250 homes destroyed

• 15 miles of railways destroyed

• 185 miles of highway destroyed

• 400 metres blown off the top of the volcano

• 47 bridges destroyed

• 12 million salmon died

• approximately 7,000 animals died

• logging camps destroyed

• largest landslide ever recorded

• at least 12 US states were affected by ash fallout
  

What were some secondary effects of the eruption?

• electricity supplies interrupted

• telephone wires cut

• 12% of the total crop was ruined by settling dust

• £100 million ash damage cost to farmers’ crops and machinery

• the timber industry in the area was destroyed by the flattening of trees

• traffic chaos caused by the ash ejected into the atmosphere

What were some immediate responses to the eruption?

• set up a 20-mile exclusion zone on March 31st 1980

• declared a state of emergency on March 31st 1980

• immediate search and rescue operation

• helicopter rescues to take casualties to hospital

• rescued 198 people

• shelter provided for those who lost their homes

• medical supplies given to the injured

• flights cancelled due to the ash ejected into the atmosphere

What were some long-term responses to the eruption?

• created the Johnston Ridge Observatory, which was opened in 1997

• money given to redevelop the salmon hatcheries

• a million tonnes of ash were removed from roads, buildings, and airports

• cost of over $1 million to remove ash

• ash removal in the town of Yakima took 10 weeks

• built new highway

• money give to rebuild houses

• forest area to the north replanted (millions of trees replanted, costing $300 million)

How is Mount St. Helens being managed now?

• seismic monitoring stations

• accelerometers

• GPS stations

• gas sampling stations

• electronic tiltmeters