Mount St Helens 1980

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Mount St Helens erupted on the morning of May 18th 1980, after being inactive for over years. It was caused by the subduction of the oceanic under the continental , on the Coast of the United States. The volcano forms part of the of mountains.

After minor earthquakes and a small eruption during , scientists carefully monitored the mountain. By the beginning of May a bulge had developed on the North side of the mountain. This activity forced the Local Authorities to create a “” around the volcano, from where any residents were evacuated, and no one was allowed to re-enter. This saved a lot of people from the disaster.

At approximately 8.30 a.m. on the 18th May, the volcano erupted a small amount of ash and stem. Then, a couple of minutes later, something occurred that nobody could have predicted. An caused the bulge to collapse down the side of the mountain. This released the full power of the explosive gases behind at as the mountain literally blew its own side off. The material from the massive sped down the mountain, filling and then racing on as a mud flow (it had mixed with the lake water) down the Toutle River and River.

The explosions from the side of the mountain sent a speeding cloud of gas, steam and dust at speeds of over kph across the ground to the North of the volcano, flattening everything in its path. It felled trees up to km away. Every form of life within this range was destroyed.This type of blast is known as a .

Study the diagram below and then answer the questions.

mtsthelens.gif

What is labelled A?

What is labelled B?

What is labelled C?

What is labelled D?

What is labelled E?

What is labelled F?