The Volcanic Eruption of Mount Saint Helens - Article Example

The volcanic eruption of Mount St. Helens is one of the most studied explosions by scientist and geologists in the last 30 years. The eruption at themountain occurred on 18 may 1980 under the watchful observation of David Johnson, a geological survey volcanologist from the United States. Sadly, the eruption claimed his life, just as he was reporting the spectacular event from his station, about 5.5 miles away from the mountain. The aftermath of the eruption was phenomenal, affecting human settlements, aquatic systems and aviation in the areas surrounding the mountain as well as distant regions where the molten lava, debris and volcanic ash landed. This paper explores the geological aspects of the eruption, focusing on the mechanics, causes and the effects of the eruption in the area. According to Glicken (14), the mountain had been calm for a long period prior to the 18 May eruption. Located in south central Washington, St Helens Mountain was a symmetrical cone with an elevation of 2950 meters up to the peak prior to the eruption. The mountain also supported about 13 glaciers (Schilling, et al, 323). Two months prior to the eruption, the United States Geological Survey in Washington reported a series of earthquakes around the mountain’s region. The first earthquake tremor on the mountain measuring 4.1 on the Richter scale was recorded in March 20 1980 (Glicken 28). After the first earthquake, over forty earth tremors per hour were recorded in the mountain by 25 March that year. Two days later in 27 March 1980, the first explosion occurred in the mountain, releasing volcanic ash and steam up to a distance of about four miles in the atmosphere (Vallance et al, 171). The explosion caused a visible crater on the peak of the mountain peak that was covered with snow. According to Glicken (38), the resulting crater measured about 250 feet wide and sixty feet deep. This observation prompted the emergency and disaster organizations in the area to start evacuating people to safety. A second eruption occurred at night of the same day, releasing steam and crushed rocks to an altitude of about four miles above the peak of the mountain. The second explosion created another crater that was observed the following day on 28 March 1980. According to Vallance, et al (173) both craters joined after a series of eruptions, forming a 2000 feet long and 500 feet deep crater. Two days later on March 20, a phreatic eruption occurred on the mountain. The phreatic eruption was caused by the contact of the rising hot lava with water melting from the ice cap resulting to a steam explosion (Glicken, 53). A series of phreatic eruptions occurred the same day accompanied by strong earth tremors varying in intensity from 3.3 to 4.4 on the Richter scale (Galvin). Following these events, the local governor declared a state of emergency and security forces were called to control the increasing number of people witnessing the event. Large-scale evacuation of people was undertaken and the access to the region blocked. Steam and ash continued emerging from the peak of the mountain in the following month accompanied by a series of smaller explosions. In April, intrusion of magma on the northern part of the summit caused a bulge that was swelling at a rate of about one and a half meters per day (Vallance, et al, 174). In early April, the mountain erupted again, releasing steam and volcanic ash upwards, to an altitude of about 15,500 feet above sea level. By the end of April, the bulge on the summit had reached an enormous size of over 400 feet high and it continued growing. On May 12 1980, an ice landslide measuring about 800 feet slid for a distance of about 1000 meters down the mountain and several days later, a series of about 40 earth tremors occurred on the volcano (Glicken, 39-46). In the morning of 18 may 1980, an earthquake with a magnitude of 5.1 on the Richter scale initiated the catastrophic explosion in the volcano. According to Vallance et al (175), the earthquake caused a 2.8 cubic kilometer landslide on the northern side of the volcano. According to Glicken (15), the cone of Mount St. Helens was the source of the landslide. The deep and wide crater formed in the previous explosions and the subsequent tremors had weakened the edifice of the mountain at the summit. The landslide exposed the bulge that had grown from the viscous magma on the northern flank of the mountain. This resulted to a cataclysmic eruption and a sudden decompression of gaseous magma that caused a lateral explosion (Glicken, 86). For nine hours, the volcano released vast volumes of magma and volcanic ash into the atmosphere up to an altitude of about 63,000 feet. According to Vallance et al (176), the blast moved at a speed of about 500 kilometers an hour, leaving a trial of destruction along its path. Several minutes after the initial explosion, a dense cloud of volcanic ash shot vertically from the volcano, raising to an altitude of about 25 kilometers in the sky. The volcanic ash formed dense clouds on the eastern part of Washington causing poor visibility. In three days, the volcanic ash clouds had crossed the United States and fifteen days later, it had circumvented the world (Vallance, et al, 176). The eruption of Mount St. Helen caused phenomenal geological, economic and environmental devastation. The enormous lateral blast destroyed and burned about 625 square kilometers of forest, comprising of mature trees in about three minutes (Vallance, et al, 171). According to Galvin, over 7000, bears, elk and deer were killed in the forest. The flourishing forest that was initially an attractive and popular tourist attraction and a rich source of timber was reduced to a wasteland (Galvin). Besides the blast, the explosion produced one of the largest mass movements in history, comprising of huge landslides of debris, lahars and pyroclastic flows that spread over large distances (Glicken, 25). In the process, the blast emitted poisonous gases and a combination of the hot debris killed 57 people. The avalanche of debris that contained hot magma, rocks, and volcanic ash entered the aquatic bodies within the vicinity of the mountain. Some of the main aquatic bodies affected by the debris in the region included the Spirit Lake, Columbia, Toutle and Cowlitz rivers (Vallance, et al, 172). The debris avalanche contaminated and interfered with aquatic ecosystems in affected water bodies. In the Spirit Lake, the debris raised the bed by over 60 meters resulting to expansion of the shoreline (Glicken, 59). The Toutle River, especially on the North Fork region recorded the highest deposition of the debris, that flowed a distance of about 23 kilometers filling the valleys with the rivers course (Galvin). The hot debris increased the temperature of the water in the lake and rivers, causing the deaths of numerous aquatic organisms. Moreover, the lahars destroyed 27 bridges and over 200 homes (Vallance, et al, 172). The deposition of lahars in shipping lanes interfered with navigation, causing many ship to be stranded in various ports including Portland, Vancouver, and Oregon for long period. After the explosion hundred of thousands tones of volcanic ash were deposited in various areas across the United States. In Washington and other urban areas, the massive ash deposits interfered with the flow of traffic by reducing visibility and rendering the roads, highways, and streets impassable. The huge volumes of ash injected in the stratosphere resulted to the suspension of all flights in the affected region. The fine ash blocked the filters of vehicles, which resulted to breakdown of many automobiles on the roads (Galvin). According to Galvin, the volcanic eruption caused an estimated loss of about $1 billion in damages. The massive landslide at the peak of the mountain reduced it by about 400 meters. Before the eruption, St Helen Mountain stood at about 2950 meters above sea level. Besides lowering the height of the mountain, the blast changed the structure of the mountain at the peak, creating new geographical features. These include formation of lava dome and the Amphitheatre glacier within the crater of the mountain (Schilling, et al, 328). Work Cited Galvin, J. “Mount St. Helens Eruption: Washington May 1980.” 30 July 2007. Retrieved on 17 November, 2011, From, http://www.popularmechanics.com/science/environment/natural-disasters/4219883 Glicken, H. “Rockslide Debris Avalanche of the May 18, 1980 Mount St. Helens Volcano, Washington.” 1996. Retrieved on 17 November 2011, from http://vulcan.wr.usgs.gov/Projects/Glicken/OFR96-677.pdf Schilling, P. et al. “Post Eruption Glacier Development within the Crater of Mount St. Helens, Washington, USA.” Quarterly Research 61(2004): 325-329. Vallance, J. et al. “Mount St Helens: A 30-year legacy of volcanism.” EOS, 91.19(2010): 169-180. (Retrieved from http://www.agu.org/pubs/pdf/2010EO190001.pdf) Read More