LuJean Eldredge
Geology T/TH
Term Paper
2/23/12
Mount St. Helens
Rising majestically toward the sky, Mount St. Helens is a strikingly beautiful sight to see. Built
over centuries from various eruptions, its peak was
once an almost perfect cone. It is located in
Skamania County, in the southern part of
Washington State approximately 50 miles north of
Portland, Oregon. It is the youngest and most
active volcano in the Cascade Range. Because of
its similar structure, Mount St. Helens has often
been compared to Mount Fuji in Japan (Foxworthy
1982).
Figure 1: Mount St. Helens
Photo courtesy of Primetab.com
Some of the Native Americans in the Northwest call it Louwala-Clough, which means,
“smoking mountain.” One of the legends told to early explorers was about a beautiful maiden named,
“Loowit.” The Great Spirit “Sahale” had two sons, Wyeast and Klickitat. They both fell in love with
Loowit, but she was unable to choose between them. They fought violently over her. This infuriated
Sahale so he buried each one in a mountain. Loowit was locked away in a beautiful cone of white
(Mount St. Helens). Wyeast was left standing strong and proud (Mount Hood) and Klickitat bent
weeping over the loss of Loowit (Mount Adams). If you hear rumblings from the mountains, it is said
to be because of their sorrow or anger. The name Mount St. Helens was given by Commander George
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Vancouver in 1792. It was named for British diplomat Alleyne Fitzherbert whose title was Baron St.
Helens (USGS 1980).
Many geologists have studied Mount St. Helens over the years. Some of them include
Lieutenant Charles Wilkes, Dwight R. Crandell, Donal R. Mullineaux, and Clifford P. Hopson. It was
discovered that ancestral Mount St. Helens began to grow before the last major glaciations of the Ice
Age had ended about 10,000 years ago. About 40,000 years ago is when the oldest ash deposits have
been dated, flowing over even older volcanic debris and sedimentary rocks. After the glaciers
disappeared, intermittent volcanism continued. Nine main pulses of pre-1980 volcanic activity have
been recognized. These periods lasted from about 5,000 years to less than 100 years each and were
separated by dormant intervals ranging from 15,000 years to only 200 years. About 3,500 years ago an
eruption formed a dam across the Toutle River creating a lake which would be the forerunner of Spirit
Lake. Between 1800 and 1857 there was a large explosive eruption which was followed by a series of
minor explosions and extrusions of lava, which ended with the formation of the Goat Rocks lava dome
(Tilling 1990). Mount St. Helens has built up and been destroyed and then rebuilt at least 3 times. The
cone formed before the 1980 eruption was only a little over 2,000 years old. Through tree-ring dating,
geologists have found that Mount St. Helens has only been dormant for two periods since 1480. In the
late 1700’s there were several decades of dormancy and then a 123 year period between 1857 and
1980. While in this dormant state the silica content of the magma increased which made for an
increased viscosity. This increased the pressure inside. As the pressure builds an eruption becomes
imminent (Dodson 1980.) Because of seismic activity, scientists in the 1960’s predicted that Mount St.
Helens would erupt again, most likely before the year 2000. An article in the Christian Science
Monitor quoted the late William T. Pecora, a former Director of the USGS, as being "especially
worried about snow-covered Mt. St. Helens" in 1968 (USDA 1980). Dwight R. Crandell and Donald
R. Mullineaux in 1978 authored a USGS pamphlet titled Potential Hazards from Future Eruption of
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Mount St. Helens. In this pamphlet they warned of future eruptions. The warning signs of an eruption
were described in detail. They mapped out areas that would most likely be affected by pyroclastic
flows, flooding, mud flows and ash fall. State leaders were informed of their findings, but the planning
efforts they made ended up being inadequate for the disaster that was to come (Dodson 1980).
Scientists weren’t exactly sure what to expect from Mount St. Helens. Volcanologist Carolyn Driedger
said, “Just as with humans, each volcano has its own personality. Some volcanoes erupt with gentle
flows of lava, and others with violent explosions of ash and gas” (Fradin 2007).
Mount St. Helens is a composite or stratovolcano. This type of volcano is formed by multiple
eruptions over time. Cinders and ash are covered by lava flows, which cool and harden. Then more
ash and cinders cover the hardened lava flow. This in turn is covered by a new lava flow. This pattern
continues forming a large, steep cone. Mount St. Helens grew to a height of 9,677 feet. Composite
volcanoes usually have very violent eruptions. Other examples of composite volcanoes include
Krakatau in Indonesia and Mount Pinatubo in the Philippines. (Silverstein 2010).
The earth’s crust is broken up into large puzzle like pieces that float on a liquid layer of molten
rock called the mantle. These plates are in constant motion, moving a few inches each year. Mount St.
Helens, along with the other volcanic mountains in the Cascade Mountain Range, was formed because
of the subduction of the Juan De Fuca tectonic plate underneath the North American plate. As the Juan
De Fuca plate slides under the North American plate a continental uplift takes place. As the Juan De
Fuca plate sinks lower into the mantle, friction and the increased temperature causes the plate to heat
up and it starts to melt. This melted rock or magma then comes to the surface, forming the volcanoes
in the Cascade Range. The volcanoes in the Cascade Range are part of the Ring of Fire that circles the
Pacific Ocean. See Figure 2 and 3 (Gellar 2008, Lauber 1986).
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Plate Tectonics of Mount St. Helens
Figure 2: Tectonic plates of Cascade Range
Figure 3: Subduction Zone
Courtesy of geomaps.wr.usgs.gov
Courtesy of Pacific Northwest Seismic Network
Because Mount St. Helens slept for so long, people were aware that it was a volcano, but they
were not afraid of it. To them it was a beautiful place to hike, camp, picnic etc. Thousands of visitors
would come each year not ever suspecting the danger that was lying beneath the surface. On March
16, small earthquakes began in the Mount St. Helens area. A magnitude 4.2 earthquake on March 20
signaled the re-awakening of Mount St. Helens. Seismic activity continued to increase (Dodson
1980). On March 27 a loud explosion was heard as Mount St. Helens began to spew out steam and
ash. Two new craters were opened up at the top of the mountain. Static electricity was seen arching
from one crater to the other. Flashes of lightning from the mountain appeared, some almost 2 miles
long. Smaller eruptions continued through April. The two new craters joined to form one new large
opening. The ash that was blown out during these initial eruptions was from a 350 year old dome that
had been shattered by these steam blasts (Tilling 1990). On May 7 the small explosions began again
continuing until May 14. Geologists were working around the clock to determine what was happening
inside. A large bulge was starting to form on the north face of the mountain. It was growing about 5
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feet a day. By mid May it was huge. Longer than a mile and half a mile wide, the bulge had ballooned
to an incredible 300 feet. (Lauber 1986) Evacuations were made. Access to the mountain was
restricted. Despite warnings by geologists and state and local leaders many people still flocked to
Mount St. Helens. On May 17, 1980 people were still camping within 8 miles of the mountain.
Logging activity still continued. Residents who had been evacuated wanted to return to their homes.
Others refused to evacuate (Bredeson 2001). Harry R. Truman refused to leave his home. He had
built cabins and a lodge at Spirit Lake below the mountains north side. He had lived there for more
than 50 years and didn’t plan on leaving. Many people, including school children wrote him letters
encouraging him to leave, but he refused. On May 18, 1980 Harry got his wish. He would never have
to leave his home. (Green 2005).
Sunday, May 18, 1980 was a beautiful spring day. Mount St. Helens was a giant pressure
cooker. At 8:32 a.m. in response to a 5.1 magnitude earthquake about a mile below the mountain, the
bulge on the north face collapsed, exploding out laterally. Tons of the mountain slid down the north
face in the largest landslide ever recorded. Part of the avalanche rushed across Spirit Lake adding 180
foot layer of debris to the bottom of the lake, but the majority flowed west into the Toutle River at
speeds up to 155 miles per hour. Geologist David A. Johnston had radioed in, “Vancouver,
Vancouver, this is it!” (Latta 2009). Seconds later he was swallowed up in the explosive blast which
traveled north of the volcano at speeds up to 300 miles per hour. The pressure cooker had been opened
and the superheated water had flashed to steam expanding violently. It snapped off 180 foot trees like
toothpicks, leveling 150 square miles of land. Beyond that other trees were left standing, but destroyed
because of the heat, all tolled destroying 230 square miles. Shortly after the lateral blast was finished
Mount St. Helens began to erupt upwards. The blast produced a column of ash and volcanic gas that
rose into the atmosphere approximately 15 miles in an explosive plinian style eruption. (Lauber 1986).
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Eighty miles away in Yakima, Washington at 9:45 a.m. the ash from Mount St. Helens
blocked out the sun and made it so dark that the street lights came on. Ash fell like snow covering the
ground. At 11:45 the same thing happened in Spokane, Washington. The eruption continued for 9
hours. Huge ash clouds traveled up to 930 miles away, depositing ash and pumice along the way.
Within two weeks, some of the ash had traveled around the world. About 540 million tons of ash fell
over an area of more than 22,000 square miles (Tilling 1990).
Figure 4: Pumice Accumulation
Figure 5: Ash Cloud Movement
Courtesy of Smithsonian
Finally there were mudflows or lahars. The heat of the blast melted the snow and ice on the
top of the mountain. This mixed with the mud and ash and created a mixture that was much like wet
cement. Moving at 25 miles per hour it destroyed roads and bridges, houses, moved cars and huge
boulders. It blocked shipping channels miles away in the Columbia River (Dodson 1980).
On May 19, Mount St. Helens was a very different place. The eruption had blown away 1,200
feet off the top of the mountain. (See Figure 6.) The north side of the mountain had a large horse shoe
shaped crater with a vent in the middle. The once green, beautiful mountain now spread out in a large
fan shaped wasteland. Fifty seven people lost their lives in the eruption including Harry Truman and
David Johnston. In 1980 Mount St. Helens erupted six more times building up a new dome (Lauber
1986).
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Figure 6: Mount St. Helens before and after
Courtesy of the USGS
In 2004 – 2008 Mount St. Helens came back to life erupting several times shooting steam and
ash into the air about 30,000 feet. These eruptions continued to build up the dome. It has since
quieted down with not much activity (Sherrod 2008).
Much has been learned from the 1980 eruption at Mount St. Helens, not only geologically, but
also ecologically. In 1982 congress set aside 110,000 acres around Mount St. Helens as a restricted
research area for scientists of all areas to come and learn. It was uncertain if and when life would
return to the devastated areas, but indeed it did and with greater speed and intensity than expected
(Funk 2010). Hopefully when another eruption comes we will have learned the lessons needed to be
better prepared than we were for this one.
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Works Cited
Bredeson, Carmen. Mount St. Helens Volcano Violent Eruption. New Jersey. Enslow Publishers, Inc.
2001. book.
Dodson, Margaret A. Notable Natural Disasters; Mount St. Helens. Salem Press. May 18, 1980. Print
Foxworthy, Bruce and Hill, Mary (1982). Volcanic Eruptions of Mt. St. Helens. U.S. Geological
Survey Professional Paper 1249
Fradin, Dennis and Judy. Volcanoes, Witness to Disaster. Washington D.C. National Geographic
2007. book
Funk, McKenzie. Mountain Transformed. National Geographic. May 2010. Print.
Gellar, Doug. Cascadia Subduction Zone Volcanism British Columbia Emporia State University.
April 2008 Print.
Green, Jen. Disasters. Mount St. Helens. Wisconsin. Gareth Stevens Publishing. 2005. Book.
Latta, Sara L. Lava Scientist Careers on the Edge. New Jersey. Enslow Publishers, Inc. 2009. book
Lauber, Patricia. Volcano The Eruption and Healing of Mount St. Helens. New York. Bradbury Press.
1986, book:
Sherrod, D.R., Scott, W.E., and Stauffer, P.H. (editors), A Volcano Rekindled: The Renewed Eruption
of Mount St. Helens, 2004-2006 2008. USGS Professional Paper 1750
Silverstein, Alvin and Virginia. Volcanoes, the Science Behind Fiery Eruptions. New Jersey. Enslow
Publishers, Inc. 2010. Book.
Tilling, Robert I., Lyn Topinka, and Donald A. Swanson. Eruptions of Mount St. Helens: Past,
Present, and Future. Washington, D.C.: Government Printing Office, 1990.
U.S. Department of Agriculture, Gifford Pinchot National Forest "Mount St. Helens" Brochure, 1980:
Government Printing Office GPO 1980
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