Geography Case Study: Mt Saint Helens – Flashcards
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MT ST HELENS: When?
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18th May 1980, am
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MT ST HELENS: Where?
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Washington state, Cascade Mountains, USA. 'Ring of Fire'
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MT ST HELENS: Signs of eruption
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Frequent seismic activity before eruption- Beginning about March 16, 1980, series small earthquakes occurred in Cascades. Large bulge on the side of Mount Saint Helens, continued to grow.
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MT ST HELENS: Plate margin type
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Destructive
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MT ST HELENS: Plates involved?
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Juan de Fuca (oceanic) North American (continental)
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MT ST HELENS: Earthquake magnitude to trigger eruption
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5.1
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MT ST HELENS: How many animals died?
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7000
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MT ST HELENS: People died?
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57
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MT ST HELENS: What happened March 20, 1980?
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Magnitude 4.2 earthquake
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MT ST HELENS: Primary effects?
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-Hot ash and gas destroyed forests and logging camps. - Lahars covered extensive area surrounding volcano. -Pyroclastic flows ran no farther than 8 km from vent but caused lots destruction, covering land and destroying trees. -15 cm ash fell in places. -520km pine forests flattened -Ash cloud 17 days travel round world -Volcano triggered giant landslide - 700mph
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MT ST HELENS: How long did plume of ash erupt?
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9 hours
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MT ST HELENS: How were the Lahars caused?
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The hot ash melted the ice
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MT ST HELENS: Secondary effects?
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-Ash blocked rivers destroying popular fishing sites + causing flooding -destroyed crops and livestock. -Flooding destroyed communications e.g. road and railway bridges -Sediment carried downstream ruined barge transport on Columbia River. -National park partly destroyed -Local tourism disrupted i.e. camp sites, hotels etc. -Farming community and locals suffered huge losses-land, £, property
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MT ST HELENS: How much ash removed from roads , airports and buildings?
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1 million tonnes
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MT ST HELENS: Short-term responses
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-Communications like roads and bridges repaired. -200 people rescued from mudflows -People rehoused.
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MT ST HELENS: Long-term Responses
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-Trees replanted cost $300 million -$70 million compensation to farmers
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MT ST HELENS: Long-term results
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-Soil fertility improved due to the ash deposits.(ENVIRONMENTAL) -Tourism has increased, boosting the local economy (ECONOMY) -The volcano is now more carefully monitored. -Rapid natural recovery
