Mount St Helens

The Eruption of 1980

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By Richard Thai
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Figure 1: A picture of Mount Saint Helens in June 1970 (Andalkar)


Before 1980, Mount St Helens was known as the "Fujiyama of America." Due to its relatively silent behavior, Mount St Helens and Spirit Lake attracted millions of visitors for recreational use. It was a beautiful mountain system full of wildlife, lakes, and foliage. It was serene, tranquil, and beautiful, but these characteristics hid the true nature of this dangerous volcano.

Basic Background


Mount St. Helens, a volcanic peak in Washington (Figure 1), belongs to the Cascade Range and is known to have caused one of the greatest geological events in North American history. This highly active stratovolcano (or composite volcano) was given the modern name of Mount St Helens by George Vancouver in 1792 (Tilling 1). Compared to other volcanoes in the Cascade Range, Mount St. Helens, is relatively a younger volcano, and lied dormant since 1857. However after several months of earthquake activities and some minor volcanic activity, due to Mount St Helens placement on an ocean-continent subduction boundary, the eruption of Mount St Helens caused one of the worst volcanic disasters in the history of the United States.

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Figure 2: Ash and other volcanic debris pour out of the volcano. (USGS)

Precursor Events

Just before the eruption of 1980, the University of Washington had just finished the implementation of a system of seismometers to aid in monitoring the Cascade volcanoes. This system began operations on March 1st, 1980. They first noticed a problem on March 20th when a magnitude 4.2 earthquake occurred beneath Mt. St. Helens. Earthquakes continued, and by March 25th magnitude fours were occurring about three times every hour. On this same day, numerous rockfalls, avalanches, and new cracks in the glacier surface were visible. For about two months after this, non-magmatic eruptions happened a few times until the devastating plinian eruption on May 18th. (6)

The Event


On May 18th, 1980, after two months of intense earthquakes, minor eruptions, a large landslide, and other tell tale signs, Mount St Helens unleashed an explosive eruption (Figure 2). It began at 8:32 am. Seconds after a magnitude 5.1 earthquake, a huge portion of the mountain was sliding away, leading to the largest landslide on Earth in recorded history (USGS). Molten material was being erupted from the volcano at about 300 miles per hour and smoke caused by the eruption was pouring out at 50-80 mph, releasing over 520 million tons of ash (USGS). Landslides, mudflows, and floods damaged the valleys and rivers around Mount St Helens and gas and ash darkened the skies, even to cities over 250 miles away, like in Spokane, Washington (Britannica). Different events were happening in a matter of seconds. After the landslides, debris avalanches were rushing down the mountainsides, causing water levels in nearby lakes to increase, which caused mudflows and floods, resulting in devastating effects.


Consequences


Large amounts of hot ash, pumice, and gas released from the eruption caused sever damages around the volcano as well as many other cities miles away. When the ash stopped falling, Mount St. Helens was left with a huge crater. The hot rocks and gas, quickly melted away much of the snow and ice, creating surges of water that contaminated river valleys, destroying trees, and man made structures. According to the USGS, 57 human lives were lost, countless non-burrowing wildlife died, over 12 million salmon died, over 200 homes were destroyed, and detectable amounts of ash covered around 22,000 square miles.

After May 18th, 1980, the land was completely changed. This event, which is considered one of the most destructive in the history of the United States, forever changed the landscape and the lives of many living in Washington. Thousands of acres of prime forest as well as many other men made structures like homes and roads were destroyed, causing many people to become homeless (Tilling). Wildlife suffered greatly for over 7,000 big game were perished in the area, Although the ash has contributed to greater yields for some agricultural crops, the ash created major problems in infrastructure by damaging transportation systems, sewage and water systems, and electrical equipment. Over 900,000 tons of ash had to be removed and the monetary losses were about $1.1billion (Tilling).

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Figure 3: 1981 photo of Clearwater Valley, a volanic blast zone after the eruption (USDA)


The eruption of Mount St. Helens burned down approximately 230 square miles of forest (Figure 3). Due to the pyroclastic flow, mudflows, and large amounts of landslides, much of the vegetation in the area were either burned to ash or swept beneath the debris. The large amounts of mudflows even held back the waters of Spirit Lake. Due to the series of natural disasters caused by the eruption, large mammals did not survive and many other birds, small animals, and insects were greatly effected. According to the U.S. Department of Agriculture, "Of the 32 species of small mammals though to be living near Mount St. Helens only 14 were known to have survived." Scientists had proclaimed that because of the tremendous amounts of organic material that fell into the waters of Spirit Lake that increased the microbial activity, depleted the supply of oxygen in the water. This caused the fish in the water of Spirit Lake to be entirely annihilated (U.S. Department of Agriculture). Almost every ecosystem around Mount St. Helen's parameters was decimated.

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Figure 4: 1987 photo of Clearwater Valley, over 4 million trees have grown in this blast zone (USDA)

Recovery


Today, much of the life forms and vegetation have regrown in the areas devastated by Mount St. Helens eruption. Within the first 5 years of the incident, surviving plants sprouted in the area. On steeper slopes, with the help of erosion, new plant species have grown. Although much of the tree species that lived on the slopes of Mount St. Helens prior to the eruption aren't as dominant as they once were, other trees and shrubs have begun to colonize the area. Insects have instantly repopulated and several species like the elk and deer have returned to the area. Several large species of birds have not returned to the blast zone area but other birds have migrated and are thriving in some of the dead tree areas. According to the U.S. Department of Agriculture, the Pacific salmon and steelhead trout had returned to Mount St. Helens to spawn in the years after the eruption, when the stream conditions improved. Surprisingly, rainbow trout and other fish are slowly repopulating and some parts of the lakes in the blast zone are opened for recreational fishing. Areas that were heavily scorched in the eruption are naturally recovering (Figure 4). Today the human population is helping the recovery process as well. The USDA Forest Service manages 110,000 acres to ensure that the devastated areas are naturally being recovered. Humans have contributed to the reforestation of the land and have helped nature bring life, vegetation, and wildlife back to Mount St. Helens. The plant and animal habitats that were affected by the eruption, living and dead, has helped accelerate the recovery. Even in areas where the eruption destroyed all life forms, small habits has developed. Plants have grown near small springs and animals, insects, and birds have colonized these once destroyed lands and has increased biodiversity.

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Figure 5: A crater is left on the north facing side of the volcano. (USGS)

Mitigation
Scientists believe that by studying the volcano's behavior, they can learn to use that behavior to guide them in mitigating the effects of future eruptions. Fortunately, Mount St. Helens's eruptive activity has made it possible for scientists to anaylize eruptive mechanisms and the volcano's magma-plumbing system, thus improving their ability to interpret volcanic deposits formed by past eruptions. Mount St. Helens is a very young volcano that is extremely active and its eruption styles vary, therefore, the deposits from its past eruptions are well preserved (kept) and yield a magnificent record of the volcano's history. Scientists combine all their information about Mount St. Helens such as: their understanding of the volcano's record, their knowledge about the volcano's magma-plumbing system and it's eruption styles to gain better knowledge about the evolution of volcanic processes over the long term at Mount St. Helens. Despite their efforts to improve mitigation, after the 1980 eruption the Army Corps of Engineers built sediment dams on the Toutle River to block mudflows, which is a serious hazard to human life and property downstream. However, this form of mitigation affected several natural processes such as the migration of fish, including salmon, to the ocean where they would spawn. Fortunately, to amend this problem, the Corps of Engineers built a fish collection facility and trucks captured salmon and steelhead upstream above the dams where the fish are released to spawn. And so you can see, even when some are trying to help mitigate effects from this volcano, things can go from good to bad and from bad to good.

Conclusion


Today the volcano is left with a massive crater left by the eruption (Figure 5). The volcano still releases small eruptions but no real explosions have recently occurred. Although the 1980 eruption devastated much of the ecosystems surrounding the volcano, nature has greatly recovered from the damages. Although many native mammals and trees were entirely wiped out by the lava, ash, and rock displacements, new species of animals and vegetation have filled the vacant spaces. Although Mount St Helens has significantly repaired its damaged earth and waters, it is believed that the volcano will one day erupt violently again. But until then, the original beauty of Mont St Helens, prior to the 1980 eruption, will one day emerge again.


References:

1. "Life Returns: Animal and Plant Recovery Around the Volcano" Mount St. Helens Teacher's Corner. 2007. U.S. Department of Agriculture.
<http://www.fs.fed.us/gpnf/mshnvm/education/teachers-corner/library/life-returns.shtml>.
2. "Mount St. Helens - From the 1980 Eruption to 2000." United States Geological Survey. 2005. PUBS.USGS.GOV.
<http://pubs.usgs.gov/fs/2000/fs036-00/>.
3. "Skiing the Cascade Volcanoes" Amar Andalkar's Ski Mountaineering and Climbing Site. 2005. SkiMountaineer.
<http://www.skimountaineer.com/CascadeSki/CascadeSki.php?name=StHelens>.
4. "Saint Helens, Mount." Encyclopædia Britannica. 2007. Encyclopædia Britannica Online.
<http://0-search.eb.com.opac.library.csupomona.edu:80/eb/article-9064866>.
5. Tilling, Robert I. Eruptions of Mount St. Helens: Past, Present, and Future. Washington D.C.: US Government Printing Office, 1984.
6. "Mt. St. Helens Eruption (1980)"
<http://www.geology.sdsu.edu/how_volcanoes_work/Sthelens.html>