Mount St Helens (MEDC)
Causes
The Juan de Fuca Plate, which is an oceanic plate (a plate underneath an oceanic or sea), moves eastward towards the North American Plate, which is a continental plate (a plate underneath land), and is forced downwards. This is called a destructive boundary, where an oceanic plate clashes with a continental plate, and the oceanic plate is forced down (because it is lighter). As the Juan de Fuca Plate moves downwards, oceanic crust is destroyed by the magma underneath the crust. The magma then builds up and pushes itself towards the Earth’s surface. The magma is expelled in the form of eruptions that happened thousands of years ago, forming Mount St Helens.
Timeline
March 20 - May 17 1980
There was a minor earthquake measured 4.1 on the Richter scale. Earthquakes continued to shake the area and on March 27, there was a small eruption of ash and steam. In May, a bulge developed on the side of the volcano, increasing by 1.5m a day.
May 18 1980
An earthquake caused the massive bulge to slide downwards forming a landslide of rock, ice and soil. As this happened, exposed magma exploded sideways out of the volcano, which moved northwards for 25km. Everything in this area was completely destroyed.
15 days later
The ash from Mount St Helens had encircled the world.
The Juan de Fuca Plate, which is an oceanic plate (a plate underneath an oceanic or sea), moves eastward towards the North American Plate, which is a continental plate (a plate underneath land), and is forced downwards. This is called a destructive boundary, where an oceanic plate clashes with a continental plate, and the oceanic plate is forced down (because it is lighter). As the Juan de Fuca Plate moves downwards, oceanic crust is destroyed by the magma underneath the crust. The magma then builds up and pushes itself towards the Earth’s surface. The magma is expelled in the form of eruptions that happened thousands of years ago, forming Mount St Helens.
Timeline
March 20 - May 17 1980
There was a minor earthquake measured 4.1 on the Richter scale. Earthquakes continued to shake the area and on March 27, there was a small eruption of ash and steam. In May, a bulge developed on the side of the volcano, increasing by 1.5m a day.
May 18 1980
An earthquake caused the massive bulge to slide downwards forming a landslide of rock, ice and soil. As this happened, exposed magma exploded sideways out of the volcano, which moved northwards for 25km. Everything in this area was completely destroyed.
15 days later
The ash from Mount St Helens had encircled the world.
![Picture](/uploads/2/4/2/2/24227451/738592704.jpg?429)
Social Impacts
The Mount St Helens eruption killed 57 people. The causes of death included trauma, the eruption blast, ash fall and lahars. A crop-duster hitting a power line, traffic accident caused by poor visibility, and two heart attacks that occurred when shoveling ash, caused 4 indirect deaths. 200-250 homes were destroyed. In Washington (the state in which the eruption occurred) 5000 motorists were stranded by the ash. The ash had to be cleared from roads and highways to let vehicles through. People living near the eruption suffered from stress, depression, lack of sleep and a sense of powerlessness.
Economic Impacts
Several logging camps were destroyed, but nobody was working, as it was a Sunday. 30 logging trucks, 22 transport vehicles, 39 railcars were destroyed along with 4.7 billion board feet of timber. Electricity was disrupted and telephone wires were cut. Also, the falling ash ruined 12 per cent of the total crop; fruit was hit the hardest. This happened because ash landed on the leaves and impended photosynthesis. The ash also blocked out the sun, making it even harder for the leaves to grow. Many livestock was lost due to flooding. Shipping had to be closed on the Columbia River and many vessels were stranded. 27 bridges were destroyed along with 15 miles of railway and 185 miles of roads. Cars could not work due to the ash clogging the engines. The International Trade Commission estimated damages to timber, civil works and agriculture to be $1.1 billion. Congress approved $950 million in emergency funds to help the recovery effort.
Environmental Impacts
Ash from the eruption filled up the near by Spirit Lake completely. It also killed all fish in nearby rivers and lakes. Every tree in the 250km squared forest and lying within the 25km blast zone north of the volcano was totally flattened and destroyed. 10 million trees had to be planted. 7000 big game animals were killed (deer, elk and bear). Glaciers on the volcano melted, mixing with the ash to form lahars.
The volcanic eruption had also created new habitats for animals and trees to live and grow in. Winds carried an estimated 1500 insect species into the blast zone, allowing them to colonize the area. The volcanic ash fertilized the soil, so the forest could grow back extremely quickly too, providing animals with a nutrient-rich feeding ground.
The Mount St Helens eruption killed 57 people. The causes of death included trauma, the eruption blast, ash fall and lahars. A crop-duster hitting a power line, traffic accident caused by poor visibility, and two heart attacks that occurred when shoveling ash, caused 4 indirect deaths. 200-250 homes were destroyed. In Washington (the state in which the eruption occurred) 5000 motorists were stranded by the ash. The ash had to be cleared from roads and highways to let vehicles through. People living near the eruption suffered from stress, depression, lack of sleep and a sense of powerlessness.
Economic Impacts
Several logging camps were destroyed, but nobody was working, as it was a Sunday. 30 logging trucks, 22 transport vehicles, 39 railcars were destroyed along with 4.7 billion board feet of timber. Electricity was disrupted and telephone wires were cut. Also, the falling ash ruined 12 per cent of the total crop; fruit was hit the hardest. This happened because ash landed on the leaves and impended photosynthesis. The ash also blocked out the sun, making it even harder for the leaves to grow. Many livestock was lost due to flooding. Shipping had to be closed on the Columbia River and many vessels were stranded. 27 bridges were destroyed along with 15 miles of railway and 185 miles of roads. Cars could not work due to the ash clogging the engines. The International Trade Commission estimated damages to timber, civil works and agriculture to be $1.1 billion. Congress approved $950 million in emergency funds to help the recovery effort.
Environmental Impacts
Ash from the eruption filled up the near by Spirit Lake completely. It also killed all fish in nearby rivers and lakes. Every tree in the 250km squared forest and lying within the 25km blast zone north of the volcano was totally flattened and destroyed. 10 million trees had to be planted. 7000 big game animals were killed (deer, elk and bear). Glaciers on the volcano melted, mixing with the ash to form lahars.
The volcanic eruption had also created new habitats for animals and trees to live and grow in. Winds carried an estimated 1500 insect species into the blast zone, allowing them to colonize the area. The volcanic ash fertilized the soil, so the forest could grow back extremely quickly too, providing animals with a nutrient-rich feeding ground.