Mount Saint Helens: May 18th 1980 Eruption

Mount St. Helens is fairly young at 40,000 years old and before 1980, has been dormant since 1857. Scientists classify Mount St. Helens as a stratovolcano, also known as a composite volcano. The volcano eruptions add layers to the mountainside, increasing the size and height after each eruption. Sometimes, like May 18th, 1980, the eruptions actually break down the size and destroy the land. These classified volcanoes are highly explosive due to their high viscosity, which means they have high silica levels and low temperatures. The danger of Mount St. Helens comes from its’ explosive nature and its’ eruption columns and famous lahars. There are around 1,000 active volcanoes located in the Ring of Fire, which are mostly formed from subduction of the Pacific Plate and other colliding plates. Mount St. Helens, along with other volcanoes in the Cascade Mountains was formed due to the subduction process (Getsinger & Nalepa).
The Cascade Mountain Range began forming 37 million years ago when the Juan de Fuca Plate subducted under the North American Plate. The Cascades are located on the United States’ West coast and travel up into Western Canada. The Cascade Arc has been home to many erupting volcanoes, but constantly changing over millions of years. The friction of the plates causes the surrounding material to melt into magma, which then moves up towards the surface.
Fortunately, geologists can identify past eruptions by studying the layers of the rock and materials layered from the eruptions so we know their affects. The growth of the Cascades has also created many faults from the continuous folding of rocks. These faults and folds cause many earthquakes throughout the Cascades. Over the 37 millions years, scientists have classified the Cascade events, which have been stop and go growth, into specific episodes. The most recent episode is The Modern Cascade Episode, which has taken place over the last 7 million years. Between 4-5 million years ago, the Arc began subducting again and has created the most recent chain of active volcanoes, including Mount. St. Helens (“The cascade episode”).
On March 20th, 1980, the dormant Mount St. Helens awoke with a small earthquake of 4.2 on the Richter scale. Geologists around the world were attracted to her frequent quakes that averaged over 25 per day. On the 27th, Mount St. Helens had her first of a few explosions that could be heard from miles away. A dense ash column rose over 2000m and a creator was left behind. Events like this occurred for the next 2 months, and progressively got worse (“Mt. st. helens). The daily log from USGS reported an increase of stronger earthquakes as they got closer to May 18th. In April, one month leading up to the devastating eruption, USGS reported a growing bulge on the north side of the mountain. The bulge eventually grew out over 400ft, sometimes exceeding 6ft per day! On May 10th, geologist reported high amounts of steam and ash that were escaping the top of the volcano. Mount St. Helens was getting ready to blow. Fifty-one days after the first explosion, all signs of life were non-existent. Law enforcement allowed property owners to go back to their homes and pack up all belongings. On the morning of May 18th, authorities were going to let another group of people back to their homes around 10am. Unfortunately, they never got the chance (“Usgs science for”).
On Sunday May 18th, the United States experienced the first part of their most recent, destructive eruption. At 8:32am, seismographs registered a 5.0 magnitude earthquake that caused the largest landslide ever recorded. The north side of the mountain broke apart and traveled at speeds over 120mph covering Spirit Lake. The massive amount of land reached 15 miles away from Mount St. Helens due to waterways and valleys (Nash, 2010). The landslide completely reshaped the mountain. Mount St. Helens was lowered over 1,500ft and now has a huge creator facing north. The landslide covered trees and killed everything in its’ path. As the landslide took place, Mount St. Helens blew it’s top (“The 1980 mount”).
Due to the loss of pressure on the north side of the mountain, Mount St. Helens erupted at an angle, destroying everything in its path. Geologists predicted a vertical release of pressure, but with the landslide, the pyroclastic flow released and headed north. A pyroclastic flow consists of hot, heavy gases and ash traveling over 200mph. Temperatures reached over 500°F in the pyroclastic flow, which lasted over 5 hours (“Narrative of Mount”, 2004). Everything within a 6-mile radius was burnt down or blown away. The blast zone consisted of 3 blast zones: Direct, Channelized and Seared. The direct zone is within 8 miles the eruption and mainly everything is destroyed. The channelized zone reaches out as far as 18 miles and due to topography, some places can have the same affect as the direct zone. The seared zone is the outskirts of where the heat and gases can be felt (Mohlenbrock, 1990). In some cases, trees can lose all of their leaves over 20 miles away. There were records of places having over 6 feet of ash covering the landscape (Nash, Making Sense of Mount St. Helens). The powerful eruption caused massive lahars and an enormous ash column.
The lahars from Mount St. Helens were fueled from the 11,000 acre-feet of water that came from the mountain’s snow and ice that slid during the avalanche during the eruption. The water mixed with debris and became a deadly wall of mud that flowed through surrounding valleys and rivers like the Toutle River. These destroyed towns and reshaped the surrounding land. The lahars dumped over 18 million cubic yards of sediment into the surrounding lakes and countryside (“The 1980 mount”). Spirit Lake was completely filled from debris, which displaced all of the water. Over a few days, the water returned back into the new Spirit Lake that was full of trees and mud. Vertically, Mount St. Helens launched a column of ash that rose over 12 miles into the atmosphere under 10 minutes. The pressure and ash released violently causing lightning and polluted the atmosphere with carbon dioxide and many other gases. Ash covered the surrounding states and fell as far as the Great Plains (“Mt. st. helens”).
After the May 18th eruption, the world just watched the news in awe. Mount St. Helens killed 57 people and injured many more. The eruption killed a large amount of wildlife, most of which we do not even see grown back today. Reports of an estimated 11,000,000 fish, 6,000 deer, 5,200 elk, 1,400 coyotes, 200 bears and many more animals died during the Mount St. Helens eruption. Even after the eruption, animals and plants were dying from the poison they inhaled. A large problem animals faced was finding food. All of the animals that escaped tried to migrate back, but died from starvation. The ecosystems are slowly growing back today, but we are not seeing the same wildlife that once surrounded the mountain. Some of the plants and trees that were covered by the mudflows are growing back. Broken branches from a few trees were able to grow roots and recover quickly. Fortunately the new trees helped with some water runoff, which has also been another problem (Mohlenbrock, 1990).
Over $1 billion were spent on Mount St. Helens’ disaster relief. Most of the money was spent on rebuilding towns and roads, moving land, and restoring power along with other necessities. Families slowly moved back into the area, but saw a major decrease in local economy from the lack of tourism. The following years lead to the construction of visiting centers and the beginning of many research projects (Volcano World, Effects on People). The geology is what is the most obvious difference of change. Over 232 square-miles of forest were destroyed, the shape of the mountain is totally different and the river systems and lakes are completely new. There is now a lava dome that occasionally erupts and rebuilds itself in the center of the crater, along with a small snowcap that is growing (Nash, 2010). There are many benefits of volcanoes, but people mainly see the negative affects of them.

Reference Cited
Mohlenbrock, R (1990). Mount St. helens, Washington. Natural History, 99(6), 26. Retrieved from Science Reference Center database.
Mt. st. Helens eruption (1980). (n.d.). Retrieved form
Narrative of mount st. helens. (2004, November 10). Retrieved from
Nash, S. (2010). Making Sense of Mount St. Helens. Bioscience, 60(8), 571-575. Doi: 10.1525/bio.2010.60.8.3
The 1980 mount st. helens eruption. (n.d.). Retrieved from
The cascade episode. (n.d.). Retrieved from
Usgs science for a changing word. (n.d.). Mount St. Helens, Washington, Precursors to the May
18, 1980 Eruption, Retrieved from
What were the effects on peple when mt. st. helens erupted?. (2010). Retrieved from

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4 Responses to Mount Saint Helens: May 18th 1980 Eruption

  1. Yin Thu Htin says:

    Excellent blog,Max!!!!!!!!! I agree with you. People only see the negative effects of volcanoes and they don’t see positive effects. But, the reason is I think they don’t know the benefits of volcanoes and me either. Before I read your blog, I also only see the negative effects of volcanoes but now I can know their positive effects and these are amazing.In my opinion, scientists should also tell these positive effects of volcanoes to the public widely like you said to me and our classmates.By the way,thanks a lot for your blog.Well done!!!!!!!!!!!!!

    • Wendy Foster says:

      Great Blog!!! One question…hmm…what happens when all of the Juan de Fuca plate has been subducted? Will volcanoes cease in the Northwest? It is a shame the number of lives lost during the eruption. I was amazed at the estimated number of wildlife deaths as well. It is a shame that when disaster stikes, it takes forever to return to normal, but it will (for the citizens, at least).

  2. ncreidler says:

    A lot of good info here i hadnt learned about before. I know we went over this eruption a little in class but it is interesting to learn a little more about such a large event that didnt happen all that long ago. Its incredible how much damage this eruption did to the surrounding forests. 232 square miles in a ridiculous amount of damage. What i think is just as impressive though is how the environment has been able to rebound since this devastating event back in 1980.

  3. walmann says:

    Impressive post! Always wanted to know more about this, since we hear about it a lot:) Very much info and a very interesting read, thank you:)

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