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by Elizagiles
Last updated 5 years ago


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Thirty five years ago Mount St Helens erupted on the 18th of May 1980, at 8.32a.m. Located in the Cascade mountain range in the state of Washington, the volcano once stood 3000m high above sea level until the explosive eruption removed 396m off the summit. Mt St Helens is classified as a composite volcano. These volcanos are prone to produce violent eruptions that pose significant danger to nearby life and property. That is why the Mt St Helens eruption is considered to be ‘the deadliest and most economically destructive volcanic event in the history of the United States’.

Two months prior to the eruption of Mt St Helens was an array of small tremors. Between March 16th and March 27th 1980, there were more than 2,800 recorded earthquakes. To monitor the earthquake activity, scientists were sent to the Cascade mountain range to sit, observe and record it's movements everyday until the eruption. Quakes of magnitude 4.0 rocked the mountain as many as three times a day and smaller quakes occurred several times an hour. These were the warning signs that a major eruption was going to occur.


As the volcano erupted it expelled large amounts of ash, rock, debris, harmful volcanic gases e.g. sulfur dioxides and steam into the air. These volcanic products reached heights of 5000m in less than 15 minutes. Oozing down the face of the mountain was a small quantity of boiling hot lava. This molton rock was generated from inside the mountain. As the pressure built up, magma was rising from underneath the earth at an excessive rate. Friction between the plates generates sufficient heat to melt the rock. This is how magma is formed before becoming lava.

What did the volcano expelled?

The sudden lateral blast removed 1,300 feet off the top of the mountain and sent huge shockwaves across the surrounding landscape. The huge blast flattened the surrounding forests, melted snow and ice and generated massive mudflows. Washington suffered severe damage as the violent eruption displaced over 900 000 tons of ash around the state. It also accumulated in an additional eleven U.S states and in seven Canadian states. In total there was approx. 230 square miles of destruction including 158 miles of highway and road damage, 200 homes were destroyed, lakes were flooded with ash rock and debris and15 miles of railways were ripped up from the ground. After the eruption was over a huge ash cloud loomed in the air for several hours, severly effecting air transport. In addition to 57 human lives that were lost, an estimated 7,000 big animals such as deers, elk and bears were also killed as well as small animals e.g. birds. The Mt St Helens eruption affected many services such as waterways and sewage. This was becasue lose debris, rock and ash was floating around for weeks on end. The total cost of damage and rebuilding efforts inflicted by the Mt St Helens eruption came to an estimated total of $1.1 billion U.S dollars. Today the land is healing, and has recovered its natural beauty however, the landscape has been permanently altered.

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Before & After

Warning Signs



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On the morning of the eruption a magnitude 5.1 earthquake ignited the forceful eruption. This was the beginning of both the lateral blast and vertical eruption that released superheated gases and ash thousands of metres into the atmosphere. The tremor caused the mountain to rattle and burst the bulge that was present on the northern face of the mountain. As the lateral and vertical eruption occurred, the volcano’s bulge and summit plunged down the side of the mountain in a huge landslide. Earthquakes and landslides were two other natural disasters that happened as the eruption was taking place.



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