when did mount st helens erupt?
18th may 1980
where is mount st helens?
Washington (USA), one of the volcanic peaks in the Cascade Mountains
what plate margin and what plates are the Cascade Mountains located on? what type of volcano is it
- destructive plate margin
- Juan de Fuca plate is being forced under the North American plate
- composite
what were the signs prior to the eruption that indicated a volcano may happen?
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
what happened on the 18th May 1980?
was a large earthquake, magnitude of 5.1, followed by a massive eruption of volcanic material - rocks, ash, hot gases, steam and lava
how far did the eruption occur?
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
what was caused by the eruption
pyroclastic flows, lahars and floods
what happened shortly afterwards the eruption?
another eruption of ash and steam - about 540 million tonnes of ash were deposited over an area of 57,000 km2
what were the economic impacts of the eruption
- 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
what were the social impacts of the eruption?
- 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
what were the environmental impacts of the eruption?
- 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
what agency performed the emergency responses?
Federal Emergency Management Agency (FEMA)
what were the short term responses following the eruption?
- face masks distributed in some areas to protect people from breathing in ash
- emergency shelters were set up for stranded and homeless people
what were the long term responses following the eruption?
-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
what was the management in the area like prior the eruption
good management and so hazardous areas were evacuated
what did the USGS (United States Geological Survey) do?
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
