Surname 1. Name: Instructor s Name: Course Number: Date: Geological Significance

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1 Surname 1 Name: Instructor s Name: Course Number: Date: Geological Significance Eruption of Mt. St. Helens in 1980 Eruption of Mt.St. Helens in the 1980s availed a significant learning experience in geology. It provided an opportunity to understand disastrous geologic processes. During the eruption, critical energy thresholds were surpassed by powerful geological processes. The processes were able to achieve significant transformations to the landscape.the eruption provided a rare chance to observe and understand the effects of disastrous geological processes.geologists who believed that geological features were formed through slow evolutionary processes were astonished to see several of these features being formed promptly at Mt.St.Helens. The eruption challenged people s way of thinking on how the geologic features form (Peter 408). At the center of research efforts, volcanologists learnt something that redefined volcanic knowledge during that time. They discovered that the collapse of the mountain was brought about by partial volcanic collapse. Furthermore, progress was also made on the techniques used for volcanic monitoring based on the studies carried out on Mt.St. Helens after the eruption. The discoveries that took place during the eruption, therefore, had a great impact on the geological society (Peter 408). Table 1 in the embeded excel document presents some characteristics of the Mt.St. Helens eruption

2 Surname 2 Figure 2: Mt.St. Helens. Source( Peter 420) Eruption of Pinatubo in 1991 Eruption of Mt.Pinatubo in the 1990s created the second largest terrestrial eruption in the 20 th century. The eruption is comaparable to the eruption Novarupta which took place in Mt.Pinatubo eruption involved a typhoon which caused a deadly mix of ash and rain in the surrounding regions. Surrouding areas were greatly destroyed by pyroclastic flow, ash deposits as well as lahars brought about by rain water which re-mobilized prior volcanic deposits. This altered river systems as well as infrastructure destruction. The eruption was considered as the largest during that time to have affected a densely populated region. The eruption produced several tonnes of magma and sulphur dioxide. It also brought large quantities of metals as well as minerals to the surface. Mt.Pinatubo eruption injected great amounts of particles into the stratosphere which can only be compared to the Krakatoa eruption in A global layer of sulphuric acid was created and global temperatures dropped. Depletion of the ozone layer also increased significantly. The eruption, therefore, has a great geological significance (Guy 1239). Table 2 in the embeded excel document presents some characteristics of Mt.Pinatubo eruption.

3 Surname 3 Figure 1: Mt.Pinatubo. Source (Guy 1250) Plate Tectonic Setting Mt. St. Helens The plate margin that led to the creation of Mt. St. Helens was destructive. The Juan De Fuca plate went below the North American plate and this brought about the line of volcanos beside the Cascade Mountain Range. Eruption of the Mt.St. Helens was, therefore, caused by the destructive disposition of the border between the Juan de Fuca oceanic plate and the N.America continental plates. The movement of tectonic plates is caused by convectional currents in the mantle. However, moving in different directions bring about diverse possible margins. With the Juan De Fuca plate and the N.American plate moving towards each other, the former went underneath the continental plate. This is due to the fact that the location of the mountain is denser as well as heavier (Peter 408). Increasing temperatures generated by magma and friction led to the melting of the crust. This led to further increase in the amount of magma. Consequenly, gas bubbles were generated, making the magma to find its way towards the surface. This generated immense pressure. The

4 Surname 4 Juan De Fuca plate went under the North American plate, and water from the ocean was forced through the subdued zone. When the water came into contact with the magma, great amout of steam was produced, making the process to be aggressively explosive (Peter 408). Mt.Pinatubo Eruption of Mt.Pinatubo was caused by collision between the Philipine Sea plate and the Eurasian plate. The type of boundary that led to the eruption was covergent. This type of boundary comes about when two plates move directly towards each other. The movement of the plates was initiated by an earth quake with a magnitude of 7.8 that had taken place a year earlier. The earthquake hastened the relaxed movement of the plates. The type of stress that led to the eruption of Mt.Pinatubo was compression. This occurs when the involved plates press on each other. The compressional forces in the eruption forced the magma to the surface (Guy 1239). Discussion Eruption of Mt. St. Helens Mt. Pinatubo had not erupted for centuries, and it was believed that it will not become active for a while longer. However, in the mid-1991, gas-charged magma appeared on its surface and spewed out to the surrrounding areas. The magma continued to come out strongly sending layers of volcano droppings down the mountain. The magma reached a height of about 22km and an area of 400 cubic kilometers. Gases and volcanic ash caused by the eruption reached many parts of the world. The volcanic eruption was followed by the collapse of the summit of the volcano. This led to the creation of a caldera. This is a kind of crater that appears on the surface of the volcano. The formation of the caldera happens on the direct hole after the collapse of summit of the volcano (Peter 408). Given that this mountain was a stratovolcano, some contextual information on stratovolcanoes can be useful in understaning Mt.St.Helens eruption. Stratovolcanoes which are at times refered to as composite volcanoes, are normally symmetrical. They assume the shape of a cone. The steepness of a stratovolcano varies in a way that creates an upward concave structure curving inwards from the the lowest point to the top of the mountain. Internally, these forms of volcanoes are usually made of alternating segments of lava flow, mudflow, ash as well as other forms of volcanic matter. Normally. Stratovolcanoes have ventilated crater walls which provides a pathway of lava. This contributes to as much as two thousand four

5 Surname 5 hundred ft increase in the height when the lava cools down. The increase in height can also be caused by conduit systems which give way to magma from the underground sources to the the surface of the earth. At times found in collisional margins among other forms of margins, stratovolcano is sometimes characterized by rapid plinian eruption which spews large amounts of toxic gas and ash into the atmosphere at very high speeds (Peter 408). Eruption of Mt.Pinatubo In the mid-1990, a powerful earthquake struck the northeast of Mt.Pinatubo. This led to the shaking and squeezing of the earth s crust underneath the mounting. The earthquake caused a cosiderable landslide at the mountain. It also caused a short-lived rise in the amount of steam emitted from a preexisting geothermal region. In the third month of the year 1991, magma rising toward the surface of the earth from underneath Mount Pinatubo prompted small earthquakes. Powerful steam explosion also occurred. Several other small earthquakes followed together with the emission of poisonous sulphur dioxide gas from the volcano. By June 1991, magma had reached the surface of the mountain. The volcano exploded later in a cataclysmic eruption that emmitted 5 cubic km of volcanic materials. Volcanic ash rose very high and was blown in all direction by cyclonic winds (Guy 1239). Similarities between Eruption of Mt. St. Helens and Mt.Pinatubo Both volcanic eruptions were caused by convergent movement of tectonic plates. Eruption of Mt. St.Helens, for instance, was caused by compressional forces of the Juan De Fuca plate and the North American plate. Eruption of Mt.Pinatubo was caused by compressional forces brought about by the convergence of the Eurasian and Philipine sea plate. The two eruptions can also be characterized as caldera (Peter 410). Differences between Eruption of Mt. St. Helens and Mt.Pinatubo The eruption of Mt.Pinatubo was many times larger than the Eruption of Mt.St.Helens. The former is therefore a major eruption while the latter is a large eruption. The two volcanic eruptions also took place in different geographical locations (Peter 410). Conclusion Eruption of Mt.St.Helens and Mt.Pinatubo have a geological significance. Mount St.Hellens, for instance, provided a chance to learn more about the the catastrophic geologic processes. Geologists gained new knowledge on the formation of geological features. Those that

6 Surname 6 believed in evolutionary processes got to know that it is not always the case. The two eruptions were caused by movement of tectonic plates. Eruption of Mt.St. Helens, for istance, was caused by the movement of the Juan De Fuca and the the North American Plates. Eruption of Mt.Pinatubo was caused by the compression forces of the Eurasian and the Philipine Sea Plates.

7 Surname 7 Works Cited Guy, Brasseur. Mount Pinatubo Aerosols, Chlorofluorocarbons, and Ozone Depletion. American Association for the Advanced Science, Aug. 2009, pp Peter, Limpman. The 1980 Eruptions of Mount St. Helens. Scientific Research Society, Mar.2010, pp