Geography Unit 4 Case Studies

Mount Saint Helens (1980)

What caused the eruption?

Located on the 'Ring of Fire'
Destructive boundary - continental plate (North American) meets an oceanic plate (Juan de Fuca)
The oceanic plate subducted underneath the continental plate because its denser, as the plane descends into the earth the plate starts to melt due to the fiction caused by the movement of plates. This melted plate, which is now magma rises through the continental plate and when it reaches the surface forms a volcano.

Time of eruption

Consequences of the eruption

Primary Impacts

63 people killed -> mainly by poisonous gases (BBC).
Lahars: poured into river systems, ripping tress from roots and destroying roads and bridges.
Argiculture -> crops were destroyed by ash -> ash provided benefits for soils (USGS).

Secondary Impacts

Umemployment -> near the region rose in the weeks following the eruption (USGS).
Leaving -> small percentage left the area because of lost of jobs due to the eruption (USGS).
Tourism -> after the event public reaction lead to a blow tourism, mostly in Washington and Oregon -> temporary as the reawaking make a appeal for tourists (USGS).
Mudflows: block all major river systems and Upper Toutle valleys
Portland harbour blocked -> destorying popualr fishing sites and causing flooding (BBC).
200 houses and cabins destroyed and damaged -> people left homeless (USGS).
Thousands of prime forst destroyed or heavily damaged (USGS).
Wildlife lost -> 7,000 big game animals perished in area, 40,000 salmon lost when swimming through turbines.
Transport problems -> highways and roads closed to the public for hours, airports in eastern Washington shut down due to ash -> thousands commerical flights cancelled (USGS).
Power blackouts -> ash caused transformers to short circuit (USGS).
Sewage systems -> plagued by ash clogging and damaged to equipment -> Moses Lake and Washington used deep wells and closed storage, water supply was minimally affected (USGS).

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