Natural Disasters

Mount St Helens

Location: Mount St Helens,

Skamania County,

Washington

Date: May 18th 1980

Time: 8:32 am

Location

Mount St Helens is an active volcano in Washington in the North-west of the

United States.

What happened?

On the 18th May 1980 at 8:32 am, an earthquake caused the entire north face of

the volcano to collapse spewing red-hot lava and volcanic ash over the surrounding

land.

Why did it erupt?

Mount St Helens is situated on a destructive plate boundary between two tectonic plates:

the North-American and Juan de Fuca plates. As the Juan de Fuca plate is a less dense

oceanic plate, it slides under the North-American plate and melts. The molten magma then rises through the North-American plates to form the Cascade Mountain range which

Mount St Helens belongs to.

magma

Juan de Fuca plate

North-American plate

Mount St Helens

plate melts

magma rises

Why did the eruption occur?

The magma from the melted plate rose to the crust and eventually enough built up to cause earthquakes and eventually to blow the top off Mount St Helens. This was the eruption.

Consequences of the eruption

PrimaryEconomic:• “most economically destructive volcanic

eruption in the history of the United States”.

• 15km3 timber destroyed

• Agriculture downwind of volcano suffered (e.g. 12 million salmon died when their hatcheries were destroyed)

Primary

Social:

• 57 people killed

• 200 homes destroyed

• 300km of main roads destroyed

PrimaryEnvironmental:• 60 000km2 covered with volcanic debris• Wildlife (deer,elk, bear, birds and small

mammals) damaged- estimated 7000 big game killed.

• Landscape said to be “more desolate than the moon”.

SecondaryEconomic:• Overall cost estimated $1.1million• Tourism trade dipped• Commercial flights cancelled from airports for 2

weeks• Timber industries suffered• Jobs lost in area• But tourism did increase in the long term

providing more jobs

SecondarySocial:• People moved away from neighbourhood• Residents left without some amenities for a while

(e.g. Water treatment, electricity and sewage removal damaged)

• Residents suffered emotional and stress problems

SecondaryEnvironmental:• Local ecosystem unbalanced• Water polluted by volcanic debris • Much of landscape is still scarred today• But the soil in the surrounding area became

more fertile

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