Mount St Helens, 1980 (HIC)

Question 1

Where is it located?

Answer 1

Washington. Far away from any major residential areas, with Portland being the largest city nearby (70km away).

Question 2

What plate boundary is it on?

Answer 2

Destructive plate boundary.

Question 3

Was any warnings made before the eruption? Why/why not?

Answer 3

Yes. In March (2 months before the eruption), a massive bulge appeared on the side of the volcano, so warnings were made.

Question 4

What was the cause of the eruption?

Answer 4

On the day, an earthquake with a 5.1 magnitude occurred. The bulge was loosened and a landslide occurred, and this resulted in a volcanic eruption with a VEI of 5.

Question 5

What was the volcano remembered for?

Answer 5

Its huge pyroclastic flow which covered an area of 16 kilometres.
Its lahars.

Question 6

How many people died?

Answer 6

57.

Question 7

How many homes were destroyed?

Answer 7

Over 200.

Question 8

What were the effects of the eruption?

Answer 8

• Over $3.5 billion worth of damage.
• 47 bridges destroyed, making it hard to evacuate.
• 298km of roads destroyed.
• Ash blocked rivers which caused flooding, damaging crops and injuring livestock.
• All life within a 27km radius was killed, all trees within a 25km radius dead.
• Soil fertility has actually increased due to the ash.

Question 9

What were the responses to the eruption?

Answer 9

• Helicopters sent to search for survivors.
• 8km exclusion zone set up around the volcano, residents told to leave.
• Buildings, bridges, and roads were rebuilt.
• Over 900,000 tonnes of ash removed from Washington highways and airports.
• Councils requested funding for mental health programs to assist those affected by the eruption.