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Eruption of Mt. Pinatubo

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    Have you ever heard of the second largest classic explosive eruption of the twentieth century? The purpose of this report is to examine the cataclysmic eruption of Mount Pinatubo in June 1991. This volcano is located on the island of Luzon in the Philippines; a mere 90 kilometers (55 miles) northwest of the capital city of Manila (Rosenbu, 2010) (see Figure 1). Specifically, this report will give a vivid description and information about the volcano. It will discuss a variety of factors related to the eruption such as the consequences and aftermath of the phenomenon.

    It will also discuss how the climate was affected by the eruption and also its influence on the hydrological cycle of the earth. Mount Pinatubo is one of a chain of composite volcanoes (see Figure 2) that constitute the Luzon volcanic arc (Wolfe, E. & Hoblitt, R. , 1999). Composite volcanoes, also called Strato-Volcanoes, are formed by alternating layers of lava and rock fragments (Oracle Thinkquest, 2011). The arc parallels the west coast of Luzon and reflects eastward-dipping subduction along the Manila trench to the west. Mount Pinatubo is among the highest peaks in west-central Luzon.

    Its former summit, at 1, 745 m [meter] elevation, may have been the crest of a lava dome that formed about 500 years ago during the most recent previous major eruptive episode. The volcano’s lower flanks, intricately dissected and densely sheathed in tropical vegetation prior to the 1991 eruptions, were composed largely of pyroclastic deposits from voluminous, explosive prehistoric eruptions (Wolfe, E. & Hoblitt, R. , 1999). The first recognized signs that Pinatubo was reawakening after a 500-year slumber were a series of small steam-blast explosions in early April 1991 (Hendley II, J. Newhall, C. & Stauffer, P. , 2005). Scientists from the Philippine Institute of Volcanology and Seismology (PHIVOLCS) intensified their monitoring of the volcano; they were soon joined by scientists from the U. S. Geological Survey (USGS) and other organizations. While evaluating the threat from the volcano, these scientists discovered that the gentle slopes surrounding Pinatubo had largely been created by countless giant mudflows of volcanic debris, known as lahars, from the powerful ancient eruptions that built the volcano (Hendley II, J. Newhall, C. & Stauffer, P. , 2005). On the morning of June 15, 1991, Mount Pinatubo exploded in the largest volcanic eruption on earth in more than three-quarters of a century. The most powerful phase of this cataclysmic eruption lasted more than 10 hours, creating an enormous cloud of volcanic ash that rose as high as 22 miles into the air and grew to more than 300 miles across, turning day into night over central Luzon (Hendley II, J. , Newhall, C. & Stauffer, P. , 2005).

    In one of the famous newspapers in the Philippines, the Manila Bulletin, a four year old girl was interviewed and said, “I thought it was the end of the world. All day long, it was dark like night. ” (Villasana, B. , 2012). Falling ash blanketed an area of thousands of square miles, and avalanches of hot ash called pyroclastic flows, or otherwise known as nuee ardente, roared down the slopes of the volcano and filled deep valleys with deposits of ash as much as 600 feet thick (see Figure 3).

    Falling ash caused thousands of roofs to collapse, clogged stream channels, made roads impassable, and created massive cleanup problems (Newhall, C. , Hendley II, J. & Stauffer, P. , 2005). Within the Pinatubo’s eruption, lahars have deposited more than 0. 7 cubic miles (3 cubic kilometers; equivalent to 300 million dump-truck loads) of debris on the lowlands surrounding the volcano, burying hundreds of square miles of land (see Figure 4). Stream channels were small and were quickly filled by lahars deposits (Newhalll, C. , Hendley II. J & Stauffer, P. , 2005). Stream channels are long, narrow, sloping troughlike depression where a natural stream flows or may flow; also known as streamway (Answers, n. d. ). Lahars from Pinatubo have destroyed the homes of more than 100, 000 people. The Mount Pinatubo eruption and its aftereffects, particularly lahars during rainy seasons, not only have taken the lives of many but also have wrought havoc to the infrastructure and to economic activities of Central Luzon. Damage to crops, infrastructure, and personal property totaled at least 10. billion pesos ($US 374 million) in 1991, and an additional 1. 9 billion pesos ($US 69 million) in 1992. In addition, an estimated 454 million pesos ($US 17 million) of business was foregone in 1991, as was an additional 37 million pesos ($US 1. 4 million) of business in 1992. From June 1991 to November 1992, means of livelihood, houses, or both were partially or wholly lost in 364 barangays (villages) (see Figure 5). About 329, 000 families (2. 1 million people), about one-third of the region’s population, lived in these 364 barangays at the same time of the 1990 census.

    In 1991, 4, 979 houses were totally destroyed and 70, 257 houses were partially damaged. The number decreased in 1992, when 3, 281 houses were wholly destroyed and 3, 137 units were partially damaged (Lacsamana, J. , Mercado, R. & Pineda, G. , n. d. ) (see Figure 6). When the 5, 770-foot (1760 m) mountain shot sulfur dioxide 25 miles (40 km) into the atmosphere, the cloud mixed with water vapor and circled the globe in twenty one days, temporarily offsetting the effects of global warming.

    Satellite images taken of the area after the eruption showed a dustlike smudge in the stratosphere (Gale: Environmental Encyclopedia, 2011) (see Figure 7). The stratosphere is the layer of atmosphere extending from about 10 km to 50km (6-30 miles) in altitude (Przyborski, P. , 2012) (see Figure 8). The sulfur dioxide cloud deflected 2 percent of the earth’s incoming sunlight and lowered temperatures on worldwide average (Gale: Environmental Encyclopedia, 2011).

    This gas cloud was chemically converted into a sulfuric acid aerosol, which was predicted to cause a 0. 5C [degree celcius] global temperature decrease (Sprod, I. E. , 1994). Pinatubo ejected about 15 million tons of sulfur dioxide into the stratosphere, where it reacted with water to form a hazy layer of aerosol particles composed of primarily of sulfuric acid droplets (Przyborski, P. , 2012). An aerosol can be defined as a system of solid or liquid particles suspended in air or other gaseous environment (Aerosol Basics, n. d. ).

    The same type of photograph from the 30th day of August 1984 was taken on August 8, 1991 less than two months after the Pinatubo eruption. Two dark layers of aerosols make distinct boundaries in the atmosphere. The estimated altitude of aerosol layers in this view is 20 to 25 km, consistent with measurements made by other space-based instruments (Earth Observatory, n. d. ) (see Figure 9). Unlike the lower atmosphere or troposphere, which extends from the surface to roughly 10km, the stratosphere does not have rain clouds as mechanisms to quickly wash out pollutants.

    Therefore, a heavy influx of aerosol pollutants, like the plume from Mount Pinatubo, will remain in the stratosphere for years until the processes of chemical reactions and atmospheric circulation can filter them out (Przyborski, P. , 2012). The hydrological cycle is the continuous process by which water is circulated throughout the earth and its atmosphere also called as the water cycle (Your Dictionary Science, n. d). Large volcanic eruptions are pretty good analogue for albedo enhancement experiments due to an enhanced loading of stratospheric aerosol (Esch, M. Graf, H. , Hagemann, S. , Jungclaus, J. , Launderer, F. , Schmidt, H. & Timmreck, C. , 2008). Albedo is the ratio of the amount of light reflected by an object and the amount of incident light; a measure of the reflectivity or intrinsic brightness of an object (Albedo Arts, n. d. ). The effect of the Mount Pinatubo eruption in June 1991 on the hydrological cycle showed a remarkable slowing in 1992 as measured by precipitation over land and associated runoff and river discharge into the ocean (see Figure 10).

    Top-of-atmosphere or TOA radiation measurements such as from the Earth Radiation Budget Satellite or ERBS show how the veil of debris that formed in or was injected into the stratosphere blocked out the sun and resulted in a significant decrease in absorbed solar radiation in the Earth-atmosphere system (Trenberth, K. & Dai, A. , 2007). ERBS was designed to investigate how energy from the sun is absorbed and re-radiated by the earth (National Aeronautics and Space Administration, 1984). This was caused by an increase in albedo by up to 0. 07 because of the reflection of up to an additional 2. 5 W m? 2 solar radiation over the following two years (Trenberth, K. & Dai, A. , 2007). June 15, 1991, an unforgettable day for so many Filipinos in the Philippines particularly the citizens who used to settled in the area where the volcano is located. The cataclysmic eruption of Mount Pinatubo, a composite volcano, has become one of the important phenomena of the 20th century. The volcano has been a great influence in so many factors such as the consequences and aftermath of the eruption.

    It turned the day into a night in the island of Luzon. The climate was also affected. With the amount of sulfur dioxide that the volcano shot into the air, the climate around the world dropped 0. 5 degree celsius and made the atmosphere colder for almost two years. It also showed a slowing in the precipitation over land and associated runoff and river discharge into the ocean as the water cycle of the earth was greatly affected by the eruption. Mount Pinatubo may have been inactive today but we never know when it will wake again and welcomes everyone with its colossal eruption.

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