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What actually caused Mount St. Helens to blow its top?

by gandolphh

!Shockers News!

What actually caused Mount St. Helens to blow it’s top?

By: Gandolph H.

Mount St. Helens Eruption

What was going on?

Many know about the eruption of Mount St. Helens. But what is not clear to many people is how this monstrous volcano actually burst it’s top off. Evidence suggests movement in the earth’s crust, lava consistency, and mineral data.

Within millions of years, tectonic plates have been moving and making significant changes and landmarks in the earth’s crust, one being Mount St. Helens. One of these huge tectonic plates include the Juan de Fuca plate, which lies off the coast of Oregon, Washington, and California. This is an example of an oceanic plate, which one might guess, lies under the ocean. Slowly, and very slowly, it is pushed under the continental plate (or land plate), creating a huge amount of heat and pressure. Once these two collide, it is now known as a subduction zone or a deep ocean trench.

Tectonic Plate subduction

What happens when they force towards each other?

Even though these tectonic plates only move about 2.5 centimeters a year, if you tally that up over 100,000 years, one plate will move about 25,000 meters. If one takes a closer look at the composition of these oceanic plates, the top is layered with packed sand. Sand is made of about 60-75% quartz crystal, or in other words, silicon dioxide. This chemical composition is what eventually causes the thickness of magma once it has melted. Oceanic plates, have a density of 3.0, while other continental plates have a density of 2.7, being composed of granite. Slowly, the oceanic plate sinks under the continental plate, which creates a massive amount of friction. As the sinking plate pushes deeper and deeper into the lithosphere, it begins to melt. The silicon, having a low melting point, melts and then rises up toward the surface, where it erupts onto the exposed land. This process is most likely to form very eruptive stratovolcanoes. It has been going on since the earth formed, right under our feet, being almost unnoticeable. Mount St. Helens was formed after this process, and it was a lesson learned.

Before the Eruption…

Activity had been swelling around the volcano. About one month before the catastrophic event, seismographs pick up small tremors and vibrations. This will only increase until a large bulge starts to show on the North side of Mount St. Helens. Geologists hypothesize the movement of magma inside of the volcano was pushing outwards on the side. This sent the message that the volcano was close to it’s breaking point since the magma had so quickly raised because of the pressure.

On the picture above, it can be seen compared to the rest of the volcano that the magma had displaced much rock, while it was forcing itself upwards in a process called stoping.

Investigating the volcano

David Johnston, a geologist working for the United States Geological Survey (USGS), was investigating the bulge from the North side. He had measured the bump as it increased in width and size and provided the USGS with much needed information. Another group moved towards the East side of the volcano, measuring the bulge from that side.

When the volcano erupted

Johnston was sleeping away in his camper on May 18th, 8:32 AM when a category five earthquake struck the mountain, triggering a massive landslide. The extreme release of gas that had been built up for all that time rapidly expanded, creating a huge lateral blast, which sent tephra and other pyroclastic material through the skies. In no more than a few seconds, the great geologist was killed by the blast. Still to this day, no remains of his camper or supplies have been found.

Yet on the East side, one scientist grabbed his camera and snapped as many pictures as he could before he decided to get out of the disaster. The lateral blast ran through everything in it’s path, choking anything living and did not run out of energy until it got eight miles away from the volcano. But this was not the only thing that followed. A huge ash cloud stretched 17 miles into the atmosphere, a massive mud flow called a lahar ran through the river, and another small pyroclastic flow followed.

David Johnston USGS

Above: David Johnston examining the volcano from the North side.

Effect Of The Eruption

After the volcano had calmed, fifty-seven people were found dead and many others injured. Forests had completely vanished as if they were toothpicks. But even after destruction came renewal. Elk, deer, and other small mammals returned to the land, once again making it fertile and well to live in. Now, the government has established the Mount St. Helens Volcanic monument, protecting its sensitive grasses, flowers, and animals.

Mount St. Helens eruption effect


Silicon Dioxide- a hard, unreactive, colorless compound that occurs as the mineral quartz and as a principal constituent of sandstone and other rocks.

Magma-hot fluid or semifluid material below or within the earth's crust from which lava and other igneous rock is formed by cooling.

Lithosphere- the rigid outer part of the earth, consisting of the crust and upper mantle.

Stratovolcanoes- volcano built up of alternate layers of lava and ash

Seismograph- an instrument that measures and records details of earthquakes, such as force and duration.

Pyroclastic Flow- a fast moving current of hot gas, ash and volcanic debris

Lateral Blast- A large volcanic blast that takes place on the side of the volcano

Tephra- rock fragments and particles ejected by a volcanic eruption

Pyroclastics- Volcanic rock fragments that are less or greater than 2 millimeters

More information on !Shockers News!: This small news article company is a new idea where I (Gandolph H.) would like to spread information about new discoveries, new discoveries about the past, and some things people might not notice. It is fully reliable, stating true and researched facts.

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423 Reviews

Points: 215
Reviews: 423

Sun Dec 20, 2015 11:30 pm
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Vervain wrote a review...

Hey there, Gandolph! Here to review this article, of course~

To start with, I'm actually really interested in vulcanology. What goes on inside the Earth has been fascinating to me ever since I was a kid, so I was really excited to see this article; I learned about Mt St Helens over the summer during one of my science courses, so I figured I'm going to tackle this!

First: I'll start by reviewing the content you present us with. Your facts are backed up well within the text, and you give some context to the reader, as well as providing them with a glossary. However, while the piece was interesting, it was difficult to follow at times as your subject matter jumped around instead of being presented in any particular order. I do like the story about Johnston being included, but it reads as a sudden jump in subject between Johnston measuring Mt St Helens and the story of his death, then back to Mt St Helens and its ecology, which isn't part of your stated material.

Also, while I do appreciate that this article isn't necessarily written as an academic piece, more as an informative and educational one, I must stress the absolute importance of citations. By including citations, you are crediting the people who did the original research, took the photographs, and provided the diagrams you use; without crediting them, your piece becomes plagiarism, as you're presenting it as if everything in it is your own. You should credit every source from which you take something.

On a final note, I would highly recommend a proofreader! There were a number of basic grammar and punctuation errors in this piece, and they detracted from my experience of reading it. Even if you just store articles away for a bit before proofreading them yourself, you'll probably be able to spot quite a few! (Examples: using "it's" instead of "its"—"its" is a possessive; "it's" is a contraction of "it is"—and using "category" instead of "magnitude" to describe an earthquake.)

I hope to see more interesting articles like this in the future, but do keep in mind that citations and proofreading are your friend when writing informative pieces! Keep writing!

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254 Reviews

Points: 5688
Reviews: 254

Thu Dec 17, 2015 2:43 am
BFG wrote a review...

Hi there Gandolph H.! Nice name; interesting spelling. ;)

I love geology! So glad someone picked a geologic topic to investigate! Thanks for that.

The facts are quite accurately represented, and I like the way you explained things like plate tectonics succinctly and understandably. The pictures and the glossary added to this. I particularly liked the forest being compared to toothpicks (exactly what the picture shows the trees looking like).

Some things to work on: watch your tenses, especially in the paragraph about "before the eruption". Keep an eye out for repetitious phrases like "In seconds, the prized geologist was instantly killed by the blast." ("In seconds" and "instantly" say the same thing.) (Also side-note: people aren't typically described as "prized" -- kind of objectifies him, no? Might want to consider a different adjective.)

Thanks for a good read! Please keep spreading the good word about geology! :D


gandolphh says...

Thanks so much!!!! I was trying to raise some money in my school so this is what is was for. I will try and edit the things you suggested. Thanks again!

The mind of man is capable of anything - because everything is in it, all the past as well as all the future.
— Joseph Conrad, Heart of Darkness