Mount St Helens, USA, 1980Mount St Helens, USA, 1980

General facts:General facts:

Location?Location? Washington, USAWashington, USA Mt St Helens lies on the destructive margin where the Juan Mt St Helens lies on the destructive margin where the Juan

de Fuca plate (oceanic) is disappearing below the North de Fuca plate (oceanic) is disappearing below the North American Plate.American Plate.

Height?Height? 8,365 ft (2,550 m)8,365 ft (2,550 m)

Age of rock?Age of rock? Over 40,000 yrsOver 40,000 yrs

The volcano is considered the most active in the CascadesThe volcano is considered the most active in the Cascades..

Mount St Helens, MapMount St Helens, Map

How was it caused?How was it caused?

The eruption of 1980 was caused at the The eruption of 1980 was caused at the destructive plate boundary between the destructive plate boundary between the North-American Plate (continental) and the North-American Plate (continental) and the Juan de Fuca Plate (oceanic).Juan de Fuca Plate (oceanic).

The eruption was triggered by the sudden The eruption was triggered by the sudden injection of magma from the Earth's injection of magma from the Earth's mantle upward beneath the volcano. The mantle upward beneath the volcano. The surge of hot, new magma reactivated the surge of hot, new magma reactivated the system beneath Mount St. Helens, and a system beneath Mount St. Helens, and a series of eruptions resulted. series of eruptions resulted.

Plate Boundary:Plate Boundary:

……

Before the EruptionBefore the Eruption

After 123 years of silence, After 123 years of silence, Mount St. Helens showed her Mount St. Helens showed her first signs of life on March first signs of life on March 20th with a 4.1 magnitude 20th with a 4.1 magnitude earthquake centred beneath earthquake centred beneath the volcano.  Most northwest the volcano.  Most northwest newspapers completely newspapers completely ignored this earthquake.ignored this earthquake.

One week later, on March One week later, on March 27th, the mountain released 27th, the mountain released its first puff of ash.  No one on its first puff of ash.  No one on the ground knew what had the ground knew what had happened at first because the happened at first because the top of the mountain was top of the mountain was encased in clouds.  The small encased in clouds.  The small explosion left a 250 foot wide explosion left a 250 foot wide crater in the otherwise crater in the otherwise perfect cone. perfect cone. 

…… In late April a In late April a

noticeable "bulge" noticeable "bulge" began to form on began to form on the north face of the north face of the mountain.  The the mountain.  The bulge was created bulge was created by  the building by  the building pressure of hot pressure of hot gases and magma gases and magma inside the inside the mountain. All mountain. All through early May through early May the bulge grew 5 the bulge grew 5 feet per day.feet per day.

Aftermath:Aftermath: The 18The 18th th May, 1980, event was May, 1980, event was

the most deadly and the most deadly and economically destructive economically destructive volcanic eruption in the volcanic eruption in the history of the America.history of the America.

57 people were killed and 200 57 people were killed and 200 homes, 47 bridges, 15 miles homes, 47 bridges, 15 miles of railways and 185 miles of of railways and 185 miles of roads were destroyed.roads were destroyed.

The ash fall created some The ash fall created some temporary but major temporary but major problems with transportation, problems with transportation, sewage disposal, and water sewage disposal, and water treatment systems treatment systems

……

Airports closed from a few days to 2 weeks due to poor visibility and ash Airports closed from a few days to 2 weeks due to poor visibility and ash acculmulation.acculmulation.

Early estimates of the cost of the eruption ranged from $2–3 billion.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 Only a small percentage of residents left the region because of lost jobs due to the eruption.due to the eruption.

Several months after May 18, a few residents reported suffering stress and Several months after May 18, a few residents reported suffering stress and emotional problems, even though they had coped successfully during the emotional problems, even though they had coped successfully during the crisis.crisis.

Initial public reaction to the May 18 eruption nearly dealt a blow to Initial public reaction to the May 18 eruption nearly dealt a blow to tourism, an important industry in Washington. tourism, an important industry in Washington.

It devastated the local economy, which was based on logging the trees of It devastated the local economy, which was based on logging the trees of the national forest that surrounded the volcanothe national forest that surrounded the volcano

Despite the Despite the devastation left behind devastation left behind on May 18th, not on May 18th, not everything in the blast everything in the blast zone was destroyed. zone was destroyed. Areas that seemed like Areas that seemed like they would never they would never recover have surprised recover have surprised scientists with the scientists with the resilience of nature.  resilience of nature.  Many animals and Many animals and plants soon found their plants soon found their way through the thick way through the thick ash to the surface. ash to the surface. Several lakes that were Several lakes that were still frozen over went still frozen over went virtually untouched.virtually untouched.