Mt St Helens case study

Background InformationMt. St. Helens is located in the North West of the USA in Washington State.It is part of the Cascade Range of mountains.The area around the mountain is a National Park which is mainly used for tourism, forestry, salmon farming and some agriculture – therefore the population density of the area is relatively lowBefore 1980, Mt St Helens hadn’t erupted for over 100 yearsThe USA is an MEDC (and was in 1980) – with a GDP per capita of over $25,000 (in 1980)Mt. St. Helens is a typical composite cone volcano - formed on a destructive plate margin where the Juan de Fuca plate is being subucted under the North American plate.

Nature of the EventFrom the spring of 1980, scientist started to record 100s of small earthquake tremors coming from the mountain. In March there were small eruptions of stream and ash from the volcano.These events attracted a large number of news reporters and tourist to the area.By early May there was a visible bulge on the northern flank of the volcano where magma was being pushed to as a result of a volcanic plug that had formed in the main vent. At 8:32 am on Sunday 18th May 1980 the eruption began following the sequence of events shown on the diagram opposite.As well as the landslide, lateral blast, pyroclastic flows and ash cloud, the heat from the eruption melted snow which covered the mountain creating lahars (a secondary hazard)

Nature of the Event

Impact of the EruptionSocial Economic Environmental

56 people were killed within the blast zoneLahars destroyed over 200 homes, 27 bridges, 185 miles of road and 15 miles of railway – severely disrupting communicationsSince the eruption, the tourist industry has grown due to the fame of the eruption

Several logging camps were destroyed12% of the total crops in the area were damaged or destroyed – fruit trees were particularly badly affectedEstimated short term economic losses in Washington State reached over $800 million – have of which was made up from the loss of forestry. The second biggest cost was that of the clean up operation $250 million

Spirit Lake was filled in by the landslide250km² of forestry was destroyedOut of 32 known species of small mammals living in area, only 14 are known to have survived (mainly burrowing mammals such as gophers)Over 250km of river ecosystem was destroyed by the lahars – killing all fish lifeOver 7,000 big game animals were killed (elk etc.)Flood risks were increased on the Toutle and Cowlitz river as their channels were choked with mud and debris.

Management & ResponsesManagement:

An exclusion zone was set up from the middle of March with red zones where no activity was allowed and blue zone where certain activities could take place such as essential farming and forestry work. In total, 2000 people were evacuated from the area. There was however a lot of public opposition to the exclusion zone and people regularly tried to evade to road blocks to get closer to the volcano.

Responses:

Immediate Long term

The National Guard flew helicopter rescue missions into the blast zone for 2 weeks and rescued 130 people.The National Guard also issued clean water, emergency food rations and medical supplies2 million gas masks were provided by the Federal Government to help prevent respiratory problemsThe ash was cleared from towns such as Yakima within 3 days

The Toutle, Cowlitz, and Columbia Rivers were dredgedOver 10 million trees were replantedThe bridges were rebuilt with a wider span in an attempt to avoid blockages from future laharsThe volcano is now monitored constantly by the USGS and clear plans have been made to prepare and warn people in the area beyond the immediate blast zone to make them aware of the risks of ash clouds