Case study 20: Eruption of Mt St Helen's volcano, USA

Question 1

What type of volcano is Mt St Helen’s?

Answer 1

Stratovolcano

Question 2

Altitude of Mt St Helen’s

Answer 2

2,950m above sea level.

Question 3

What were the events leading to the 18th May, 1980 eruption?

Answer 3

Juan de Fuca plate (oceanic) moved east and was subducted under the North American plate (continental). This lead to a magnitude 5.0 earthquake which caused the North face of the volcano to collapse.
The volcano then erupted ash, producing pyroclastic flows. (hot gas and ash)
400m was blown off the top of the mountain, leaving a 500m deep crater.

Question 4

What were the environmental impacts of Mt St Helen’s eruption?

Answer 4

Every plant+animal 25km north of the volcano was killed.
Ice on top of the volcano melted, creating mudflows, choking rivers and killing fish. e.g. Spirit lake was filled with mud.

Question 5

What were the social impacts of Mt St Helen’s eruption?

Answer 5

57 deaths
250 homes destroyed
Electricity supplies cut.

Question 6

What were the economic impacts of Mt St Helen’s eruption?

Answer 6

Damage to farmers totaled 100 million pounds.
15cm of ash fell: traffic+cancelled flights.
Timber industry in the area was destroyed.
Tourism experienced a decrease - fear of another eruption + destroyed landscape.

Question 7

What were the short term responses after Mt St Helen’s eruption?

Answer 7

Authorities rescued stranded people, provided shelter, and gave medical aid.
Mobilised 198 people.

Question 8

What were the long term responses after Mt St Helen’s eruption?

Answer 8

Ash removal in the town of Yakima: $1 million.
Tree replantation: $300 million.
Compensation to farmers: $70 million
New tourist facilities to rebuild local economy.
New highway built: $7 million