Volcano- Case Study: Mt St Helens, 1980

General Information

Location: Washington State, United States of America, along a destructive boundary where the Juan de Fuca plate converges into the North American plate.

Magnitude: VEI 5

Causes: 2-month series of earthquakes and steam-venting episodes (due to injection of magma at shallow depth below the volcano that created a huge bulge & a fracture system on Mt St Helen’s northern slope.

Effects: lava flows and ash filling in Spirit Lake and log jams and ash blocking the channel of the Toutle River; sediment carried downstream ruined barge transport on the Columbia River

57 people died in the eruption - most from poisonous gases

Large number of wildlife were killed by the blast and the volcanic ash with nothing surviving in the blast zone

Flooding destroyed communications, resulting from blocked rivers washed away road and rail bridges

crops were ruined and livelihoods of loggers were devastated with large areas of trees being flattened like matchsticks.

An earthquake before the volcano’s eruption cause the entire weakened northern face to slide away, exposing the partly molten, gas- and steam-rich rock in the volcano to lower pressure.

Predictions: USGS scientists convinced local authorities to close Mt St Helen’s to the general public & to maintain the closure in spite of pressure to re-open it, saving thousands of lives.