Tsunami,Their Causes and Results - Essay Example

Tsunami I. What is a Tsunami a. The word “Tsunami” is often unfamiliar to those individuals who live far from the coast and the cause of nightmares for those who live on it, especially in communities where adequate warning and preparation systems are not in place. b. This strange looking word is pronounced tsoo-nah-mee and is derived from two Japanese words – tsu meaning ‘harbor’ and nami meaning ‘wave’. (“Tsunami”, 2006). c. Using a Japanese word for these types of waves is considered appropriate because most of the tsunamis that occur do so in the Pacific Ocean and near Japan. (“Tsunami”, 2006). d. In the past, tsunamis were sometimes referred to as ‘tidal waves’ by the general public, and as ‘seismic sea waves’ by the scientific community. (Boork, 2005). e. These terms are considered incorrect, however, since tides are the result of gravitational pulls from the moon, sun and other planets in our solar system and seismic sea wave indicates a wave generated by an earthquake. While tsunami impact can be influenced by tide and generation can occur as the result of earthquake, other factors can be involved. (Boork, 2005). II. Causes of Tsunami a. Studies into the causes of tsunamis have revealed that there are actually many different factors that can lead to tsunami generation – including the already mentioned earthquake – but not every earthquake causes a tsunami and not every tsunami is caused by earthquake. b. Earthquakes can cause tsunamis. It is generally believed that earthquakes that move in a vertical direction are more likely to cause tsunami, but Dr. Tony Song from the NASA Jet Propulsion Laboratory has shown how “horizontal motions of continental slopes confer five times the energy of a vertical displacement.” (Mayer, 2006), indicating that movement of the continental margins should be the focus of tsunami detection. c. Landslides are another possible cause of tsunamis, whether they occur above or below the water level. Landslides that occur above water and slide into the water can cause tsunamis while underwater landslides can cause a high degree of water displacement. These landslides can be caused by excessive flooding or, more commonly as global warming continues, due to the melting of layers of permafrost. Sometimes underwater landslides work in combination with earthquakes to cause tsunami. “For example, submarine slope failures can be triggered by much smaller earthquakes which could not cause a tsunami by themselves.” (Lauterjung cited in Mayer, 2006). d. A third way in which tsunamis can be generated is with the eruption of volcanoes, again with equal devastating effect regardless of whether the volcano exists above or below the water level. “Tsunamis started by this process are uncommon, but present a real threat to residents of the lower Cook Inlet region, the Alaska Peninsula, and the Aleutian Islands.” (Haeussler, 2006). e. Finally, tsunamis can also be caused by meteors. Like landslides their locations and severities can vary widely, but meteor-generated tsunamis have a greater chance of traveling long distances. f. Characteristics of tsunamis caused by earthquakes and volcanoes are that they travel long distances from the earthquakes epicenter and strike coastlines thousands of miles from their generation point. (Haeussler, 2006). As might be guessed by the nature of landslide-generated tsunamis, they are typically localized to the area in which the landslide occurred, but also more powerful. It is important to note that these tsunamis remain as difficult to predict as earthquake-generated tsunamis, particularly in the case of trying to identify potential underwater landslide regions. III. Examples of Tsunamis a. A tsunami struck the west coast of the United States in 1964 following a vertically moving earthquake that measured, depending upon the scale used, somewhere between 8.6 and 9.2 with its epicenter near Prince William Sound. The resulting tsunami traveled at more than 400 miles per hour to as far away as Hawaii and California. Tsunami-related deaths included 122 people in Alaska, 10 people in Crescent City, California and 6 people in Oregon. (Irvine, 2004). b. “On July 9, 1958, in Lituya Bay, Alaska, a large earthquake started a giant landslide that ran into the head of the bay and generated a tsunami. The wave ran up a mountainside on the opposite side of the bay to a height of more than 1,720 feet. Two fishing vessels anchored in the bay were sunk and two people died.” (Haeussler, 2006). c. A tsunami that struck Papua, New Guinea in 1998 was determined to have been caused by this same combination of earthquake and landslide. The earthquake measured only a 7.1 on the moment magnitude scale, placing it solidly in the medium range and not likely to cause the four-story high, until it was determined an underwater landslide had been triggered which, in turn, caused the wave. This tsunami destroyed the northern coastline and carried away more than 2,500 people in the three waves that struck. (Monastersky, 1998). d. A major collapse of a lava dome occurring at the Soufrière Hills Volcano in Montserrat generated a tsunami, which was recorded on Montserrat 2-4 km from the generating area and Guadeloupe, 50 km from Montserrat. e. The most recent tsunami disaster was the series of waves that struck at the Indian Ocean coastline at the end of 2004. Countries that were affected by these earthquake-generated tsunami include India, Indonesia, Malaysia, Maldives, Myanmar, Sri Lanka, Thailand, and Somalia. The inrushing water killed more than 280,000 people in towns and villages all along the coast and more than 3 million had their livelihoods destroyed prompting worldwide relief efforts. IV. Mechanics of Tsunami a. Tsunamis are usually not a single wave, but rather a wave train, or a series of waves, that are formed in a body of water by an impulsive disturbance that vertically displaces the water column. b. While still in the open ocean, tsunamis can travel at speeds excelling 450 miles per hour with wavelengths that reach several hundred miles. Because they are a series of waves, it is important to understand that the period between crests of tsunami waves can vary greatly, from one every five minutes to one every hour or so. c. The first landward side indication that a tsunami might be approaching is a sharp swell, like a storm swell, of water, followed immediately by a sudden outrush of water from the coastline that usually exposes normally underwater offshore areas. This occurs as the first wave trough reaches the area. d. At sea, there are indications within the form of the wave itself that also indicate it is approaching land. The crests are slowed, which causes their length to become shorter and their height to rise, sometimes even higher than skyscrapers. The height is largely dependent upon the type of shore the wave is approaching. e. Gently sloping shores, submarine ridges and coastal embayment tend to spur higher waves. Depending on the depth and slope of the coastline, it is also possible for the tsunami waves to wash over the shore like a flood or rapid current, as they did in Southeast Asia. (Dutkiewicz, 2005). For obvious reasons, coasts and islands with sudden, steep margins or that are surrounded by barrier reefs are safer than shallow shores open to ocean as the reefs tend to absorb a great deal of the waves’ impact and deeper coastlines do not lead to the same slowing and building of the wave form that shallow coastlines do. V. Body 4 – Guarding against Tsunami a. Although tsunamis are virtually impossible to predict, it has been argued that much of the loss of life that occurred during the 2004 tsunami that struck the Indian Ocean could have been prevented had an early warning system been in place similar to that firmly established in the Pacific. b. The Pacific Tsunami Warning System is comprised of a complex network of at least 26 seismic-monitoring stations and sea-level gauges that are designed to detect earthquakes and abnormal or sudden changes in sea level. A warning center operates from Hawaii to issue warnings for potential tsunamis in the Pacific Ocean while another center exists dedicated to monitoring any changes in Alaska. c. Once an event has been detected by the system that could potentially lead to tsunami generation, personnel within the centers interpret the information being provided and conduct quick data gathering messages from centers closer to the site of the event and watch bulletins are sent to dissemination agencies such as civil service and military groups. d. When the reports coming in from tide monitoring stations indicate a tsunami does pose a threat to any of the Pacific communities, warnings are sent out to the public via radio, outdoor warning sirens and other means and service agencies prepare to follow through on previously developed evacuation and rescue plans. e. If tide station reports later indicate a negligible tsunami or no tsunami has been generated, the warning system issues a cancellation. f. Because it is the continuing goal of this truly international system to protect as many lives as possible, the agencies involved work diligently to increase tsunami awareness and preparedness within endangered communities. VI. In Conclusion a. Tsunamis are not single super tidal waves nor are they necessarily seismic sea waves. Instead, they are a series of waves that are influenced by tide and shoreline, but can be caused by a variety of factors. b. The causes of tsunamis are most often vertically shifting earthquakes, but evidence exists that horizontally shifting earthquakes, landslides above and below water level, volcanoes and meteor strikes can also cause these waves. The cause of the tsunami and shape of the shoreline it is approaching largely determine the size and destructive force the waves will contain. c. Several examples exist within the past 100 years of most of these types of tsunamis, including the devastating occurrence in the Indian Ocean in 2004. d. Because of the way they form, tsunamis can be difficult to recognize in open ocean as they travel quickly as a long, low wave, but begin to take shape and form as they approach shore. Shallow shores lead to more devastating wave formation as the wave is forced to slow and build, sometimes to awe-inspiring heights. e. Since tsunamis cannot be adequately predicted as they are the result of unknowable natural phenomena, the best defense against them for coastal areas is the installation of a sophisticated warning system that includes several stations monitoring earth movements, communications systems that enable center personnel to closely monitor any abnormal behavior, warning systems that alert both the public and response agencies of the potential danger and proper planning prior to the strike. Works Cited Boork. “Welcome to Tsunami.” University of Washington, March 29 2005 < http://www.ess.washington.edu/tsunami/index.html> Dutkiewicz, Jan. “Tsunami 101.” Tsunami: When the Ocean Roars. 2005. Canadian Geographic Enterprises. May 1, 2006 < http://www.cangeo.ca/tsunami/tsunamis101.asp> Haeussler, Peter. “Dangers of Tsunamis.” Earthquake. 2006. US Geologic Survey / Alaska Sea Grant. May 1, 2006 < http://www.uaf.edu/seagrant/earthquake/tsunami.html> Irvine, Tom. “Prince William Sound, Alaska: Earthquake of March 27, 1964.” Vibration Data. (2004). May 1, 2006 < http://www.vibrationdata.com/earthquakes/alaska.htm> Mayer, Andreas. “Causes of Tsunami Still Cause Controversy.” DW World. (April 26, 2006). May 1, 2006 < http://www2.dw-world.de/southasia/germany/1.179924.1.html> Monastersky, Richard. “Waves of Death.” Science News Online. (October 3, 1998). May 1, 2006 < http://www.sciencenews.org/pages/sn_arc98/10_3_98/bob2.htm> “Tsunami.” Penn State. 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