Transcript Mt. St. Helens Eruption. Causes

Mt. St. Helens Eruption
Causes
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.
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.
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.
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:
1. 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.
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.