A-level case study on the 1980 eruption of Mt St Helens

2. Mt. 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 low
Before 1980, Mt St Helens hadn’t erupted for over 100 years
The 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.

3. From 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)

5. Social Economic Environmental
56 people were killed within Several logging camps were Spirit Lake was filled in by the
the blast zone destroyed landslide
Lahars destroyed over 200 12% of the total crops in the 250km² of forestry was
homes, 27 bridges, 185 miles area were damaged or destroyed
of road and 15 miles of destroyed – fruit trees were Out of 32 known species of
railway – severely disrupting particularly badly affected small mammals living in area,
communications Estimated short term only 14 are known to have
Since the eruption, the tourist economic losses in survived (mainly burrowing
industry has grown due to the Washington State reached mammals such as gophers)
fame of the eruption over $800 million – have of Over 250km of river
which was made up from the ecosystem was destroyed by
loss of forestry. The second the lahars – killing all fish life
biggest cost was that of the Over 7,000 big game animals
clean up operation $250 were killed (elk etc.)
million Flood risks were increased on
the Toutle and Cowlitz river as
their channels were choked
with mud and debris.

6. Management:
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 The Toutle, Cowlitz, and Columbia Rivers were
missions into the blast zone for 2 weeks and dredged
rescued 130 people. Over 10 million trees were replanted
The National Guard also issued clean water, The bridges were rebuilt with a wider span in
emergency food rations and medical supplies an attempt to avoid blockages from future
2 million gas masks were provided by the lahars
Federal Government to help prevent The volcano is now monitored constantly by
respiratory problems the USGS and clear plans have been made to
The ash was cleared from towns such as prepare and warn people in the area beyond
Yakima within 3 days the immediate blast zone to make them aware
of the risks of ash clouds