Mt. St. Helens Eruption. Causes

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Mount St.Helens
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Mt. St. Helens EruptionCauses
Mt. St. Helens is situated in the Rocky Mountains
near the west coast of the USA. It lies near to a
destructive plate boundary where the Juan de Fuca
Plate is moving south-east and the North American
Plate is moving north-east. As the small plate is
being forced under the larger plate it is going
into the mantle where it melts. When this
happens, molten rock rises into the crust. It
builds up in the magma chamber and eventually
forces its way to the surface.
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Impact On Landscape
After the start of the May 18th eruption, an
enormous column of ash thrust 15 miles into the
sky. It continued to eject ash for about nine
hours. The plume deposited ash and pumice on top
of the blast deposit downwind from the volcano.
The ash was blown eastward by the wind at about
60 miles per hour. Some of the ash reached the
eastern United States within 3 days. Small
particles entered the jet stream and circled the
Earth within two weeks. The blast killed every
form of plant and animal life for a distance of
25km north of the volcano. Even fully-grown fir
trees were flattened, up to 30km away. About 7000
animals died , including elk and bears.
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Impact on the People
The damage caused by the eruption ran into the
billions and 61 people were killed with 198
needing rescued. Farms were destroyed and the
entire area was covered in ash and left in
darkness. The ash caused a lot of pollution
putting the peoples health at risk. Some people
were swept away by land slides.
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Human Responses

• The nature and severity of Mt. St. Helen eruption
  surprised everyone and its effects were
  devastating. Although many charities were
  involved in the relief work, the biggest aid
  agency was the government and the Federal
  (national) government. This is called official
  aid. It fell into three categories
• Aid in preparing for the eruption
• The state authorities evacuated people from
  the exclusion zone, which saved many lives. A few
  residents, however, refused to leave, as did the
  scientists, reporters and cameramen who were only
  there for the eruption.

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2. Short term aid after the eruption This
involved (a) rescuing stranded people (b) and
then clearing up afterwards. The authorities were
able to mobilise many people and much equipment
quickly to help in these operations. 3. Long term
aid This was concerned with returning the
area to what it was originally like before the
eruption, and this took several years.