Transcript Mount St Helens, USA, 1980

Mount St Helens, USA, 1980
General facts:


Location? Washington, USA
Mt St Helens lies on the destructive margin where the Juan
de Fuca plate (oceanic) is disappearing below the North
American Plate.

Height? 8,365 ft (2,550 m)

Age of rock? Over 40,000 yrs

The volcano is considered the most active in the Cascades.
Mount St Helens, Map
How was it caused?


The eruption of 1980 was caused at the
destructive plate boundary between the
North-American Plate (continental) and
the Juan de Fuca Plate (oceanic).
The eruption was triggered by the sudden
injection of magma from the Earth's
mantle upward beneath the volcano. The
surge of hot, new magma reactivated the
system beneath Mount St. Helens, and a
series of eruptions resulted.
Plate Boundary:
…
Before the Eruption


After 123 years of silence,
Mount St. Helens showed her
first signs of life on March
20th with a 4.1 magnitude
earthquake centred beneath
the volcano. Most northwest
newspapers completely
ignored this earthquake.
One week later, on March
27th, the mountain released
its first puff of ash. No one on
the ground knew what had
happened at first because the
top of the mountain was
encased in clouds. The small
explosion left a 250 foot wide
crater in the otherwise perfect
cone.
…

In late April a
noticeable "bulge"
began to form on
the north face of
the mountain. The
bulge was created
by the building
pressure of hot
gases and magma
inside the
mountain. All
through early May
the bulge grew 5
feet per day.
Aftermath:



The 18th May, 1980, event
was the most deadly and
economically destructive
volcanic eruption in the
history of the America.
57 people were killed and 200
homes, 47 bridges, 15 miles
of railways and 185 miles of
roads were destroyed.
The ash fall created some
temporary but major
problems with transportation,
sewage disposal, and water
treatment systems
…

Airports closed from a few days to 2 weeks due to poor visibility and ash
acculmulation.

Early estimates of the cost of the eruption ranged from $2–3 billion.

Only a small percentage of residents left the region because of lost jobs
due to the eruption.

Several months after May 18, a few residents reported suffering stress
and emotional problems, even though they had coped successfully during
the crisis.

Initial public reaction to the May 18 eruption nearly dealt a blow to
tourism, an important industry in Washington.

It devastated the local economy, which was based on logging the trees of
the national forest that surrounded the volcano

Despite the devastation
left behind on May 18th,
not everything in the
blast zone was
destroyed. Areas that
seemed like they would
never recover have
surprised scientists
with the resilience of
nature. Many animals
and plants soon found
their way through the
thick ash to the surface.
Several lakes that were
still frozen over went
virtually untouched.