Mt St Helens Case Study

Question 1

when did mount st helens erupt?

Answer 1

18th may 1980

Question 2

where is mount st helens?

Answer 2

Washington (USA), one of the volcanic peaks in the Cascade Mountains

Question 3

what plate margin and what plates are the Cascade Mountains located on? what type of volcano is it

Answer 3

• destructive plate margin
• Juan de Fuca plate is being forced under the North American plate
• composite

Question 4

what were the signs prior to the eruption that indicated a volcano may happen?

Answer 4

from march 1980, signs that an eruption could happen soon - was small earthquakes, a bulge appeared on the side of the volcano and ash and steam were released

Question 5

what happened on the 18th May 1980?

Answer 5

was a large earthquake, magnitude of 5.1, followed by a massive eruption of volcanic material - rocks, ash, hot gases, steam and lava

Question 6

how far did the eruption occur?

Answer 6

600km2 fan-shaped area north of the volcano (blast zone)

-all vegetation and buildings were destroyed in blast zone which reached up to 30km away from the volcano

Question 7

what was caused by the eruption

Answer 7

pyroclastic flows, lahars and floods

Question 8

what happened shortly afterwards the eruption?

Answer 8

another eruption of ash and steam - about 540 million tonnes of ash were deposited over an area of 57,000 km2

Question 9

what were the economic impacts of the eruption

Answer 9

• total cost of $1.1 billion
• over 200 homes and cabins were destroyed and more damaged
• airports temporarily closed - over 1000 commercial flights cancelled
• lots of money spent on clearing ash from roads and runways - $2.2 million to clear ash in Yakima
• 27 bridges, 24km of railways, 300km of roads destroyed
• timber industry was severely affected by destruction of forest

Question 10

what were the social impacts of the eruption?

Answer 10

• 57 killed - mainly by inhaling volcanic ash
• 100s of people lost their homes
• unemployment rose tenfold at first - didn’t return to normal once clean-up operations began
• social facilities and recreational sites were destroyed
• some people experienced emotional stress

Question 11

what were the environmental impacts of the eruption?

Answer 11

• almost 240km2 of forest was destroyed
• wildlife suffered - around 7000 big game animals and thousands of birds were killed
• 12 million young salmon were killed
• sediment dumped in Spirit Lake raised the lake bottom by over 90m and water level by 60m
• water quality was temporarily reduced

Question 12

what agency performed the emergency responses?

Answer 12

Federal Emergency Management Agency (FEMA)

Question 13

what were the short term responses following the eruption?

Answer 13

• face masks distributed in some areas to protect people from breathing in ash
• emergency shelters were set up for stranded and homeless people

Question 14

what were the long term responses following the eruption?

Answer 14

-ash clean-up operations were organised - around 900,000 tonnes of ash were removed from roads, buildings and airports
-shipping channels were cleared of sediment to restore shipping and some new channels were cut
-45,500 acres of land have been replanted with more than 18.4 million trees
-domestic water supplies were monitored
to ensure they weren’t contaminated

Question 15

what was the management in the area like prior the eruption

Answer 15

good management and so hazardous areas were evacuated

Question 16

what did the USGS (United States Geological Survey) do?

Answer 16

when earthquakes began in march, they started a round-the-clock monitoring system - included gathering seismic data and measuring the rate of bulge growth, ground temp and sulfur dioxide gas emissions
-volcanic and seismic activity reports were issued daily