Volcanic Eruption Case Study - Geography GCSE

Location: Mount st Helens, Washington

Date: 18th May 1980

Time: 8:32 AM

The volcano is on a destructive plate boundary
The Juan de Fuca plate subducted under the North American Plate 

An Earthquake measuring 5.1 on the Richter Scale under the volcano caused it to become unstable
- This caused a landslide/avalanche on the North side of the mountain

The volcano erupted with a sideways blast with pulverised rock, ash and glacier ice and produced pyroclastic flow - currents of hot gas and ash 

Primary effects
400m was blown of the top of the mountain

Every plant and animal within 27km north of the eruption died

Every tree within 30 km of the volcano was uprooted and flattened

Secondary effects

The water produced from melting ice and snow created mudflows
These choked the rivers and killed all fish and water life

A lake was filled with mud, killing 12 million Salmon 

- the ash that had fallen eventually made the soil more fertile (positive impact)

Primary Effects

57 people died

250 homes, 47 bridges, 15miles of railway and 185 miles of road was destroyed
Telephone lines and electricity supplies were damaged

15cm of ash fell

Secondary Effects

The fallen ash clogged up car engines and farm machinery
There was traffic chaos on the roads
- The cost of damage to farmers totalled approx. £100million

Airline flights had to be cancelled 

The timber industry in the area was destroyed
 
Tourists stopped visiting - damaged economy 

Helicopter mobilised to search and rescue those in the area of the eruption
-200 people were rescued 

Shelter provided for those who had lost homes

Medical supplies given to injured

Ash was cleared to allow the traffic to flow within 3 days of the eruption

Buildings and bridges rebuilt
- a new highway built and major repairs done

Millions of trees replanted, and fallen trees removed

New tourist faculties built - attempts to bring back tourist industry
-more tourists visit now than before the eruption
-recieves 3 million tourists each year

Money was given to redevelop salmon hatcherers and compensation given to farmers