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Eric Shafer
Earth Science Honors
Mr. Leone
March 6, 2006
Earth Science Research Paper
On December 24, 2004, at 7:58 local time, an undersea earthquake occurred along the boundary between the India plate and the Burma plate. A tsunami was generated from the elastic rebound of the plate, generating a tsunami wave carrying an estimated seven cubic miles of water, and sending it out from the epicenter. Due to the lack of a tsunami warning system in the Indian Ocean, the tsunami destroyed many unsuspecting villages in Indonesia, India and even Africa. The death toll was eventually estimated at 230,000 people (http://www.tsunamispecialenvoy.org/country/humantoll.asp), making it one of the most deadly disasters in Earth's history. The earthquake was not preventable, but perhaps much of the damage was. The earthquake was caused by the subduction of the India Plate under the Burma plate, which caused the friction and stress that generated the earthquake. Instead of being a completely unpredictable and random event, the earthquake was caused by predictable and observable processes within the Earth itself.
The Earth's crust is comprised of many slabs, called tectonic plates. These plates are constantly moving, due to convection currents within the Earth itself. As the plates grind and push against each other, several things can happen. First, they can become a transform boundary, where the plates move alongside each other. In this situation, there is a large potential for earthquakes, but no subduction or melting. An example of a transform boundary is the San Andreas fault. The second possibility is that the plates move apart, creating a divergent plate boundary. This is where new crust for the Earth forms, and there is little potential for earthquakes here. The magma simply liquefies from pressure relief melting, and then oozes out through the ocean floor, forming new crust. The third possibility is that the plates move directly against each other, forming a convergent plate boundary. In this situation, one plate dives beneath the other, creating a subduction zone. There is a large possibility for earthquakes in this situation, and melting also occurs in this situation. This is the type of boundary where the Indonesian earthquake occurred. The plates grinding against each other created a subduction zone, a common situation in the Pacific Ocean. The two converging plates caused grinding, and one plate eventually slipped below the other. This process was not smooth however, and the massive amounts of friction there caused many earthquakes and volcanoes. (http://pubs.usgs.gov/gip/dynamic/dynamic.html) Around the Pacific Ocean, the Pacific Plate and the surrounding plates meet, and the Pacific Plate subducts under those plates. This area of subduction around the Pacific Ocean is known as the Ring of Fire, since many of the world's volcanoes are located there. Also along the Ring of Fire is the Sundra Trench, the trench formed by the India plate subducting under the Burma plate. This faultline is thousands of miles long, and on December 24th, part of the fault slipped.
When this fault slipped, an area about 750 miles long fell fifty feet as the India plate moved downwards. As the plate fell, it generated an earthquake with an estimated magnitude of 9.15. While this magnitude is incredibly high, it caused relatively little damage by itself, since it occurred in the middle of the ocean. The ground shook, and some buildings were destroyed on the neighboring islands, but little else. People felt the earthquake, but largely ignored it, since earthquakes consistently occur in these regions, but rarely are regarded as significant. However, this earthquake and the subsequent moving of plates displaced seven cubic miles of water, and sent it moving at a high rate of speed out from the epicenter. The shallow epicenter of the tsunami contributed greatly to its height, as the water built up faster. The massive waves began moving out from the epicenter, racing across the globe. There was little warning for the coastal areas that a tsunami was coming. For boats out in the water, there was hardly any difference, except for what most perceived as a normal wave. As the tsunami approached shallower water, however, the tsunami began to build up height. The ocean receded from the coastal areas, as the trough part of the wave hit first. The tsunami gained even more height and power from this, and when it made landfall, it had a height of about 100 feet. With no warning, many of the local residents were on the beaches, especially after the mysterious receding of the ocean. The tsunami crashed onto the beaches, submerging most of the coastline in water. A common misconception about the tsunami is that it consisted of one wave, with height, but little length. Many assume the tsunami hit like a normal wave, and then passed quickly. In reality, the tsunami came, and after the wall of water hit, more water continued coming onto the shore. The tsunami went deep inland, in some cases over a mile. When the tsunami and water finally did recede, it dragged everything back out to sea, including trees, cars, homes and people. However, the first tsunami wave was only the beginning. More tsunamis occurred throughout the day, with the third one being the largest, followed by many smaller tsunamis. These smaller tsunamis were generated from aftershocks, which continued to rock the region for months afterwards. The most famous one that is considered an aftershock is the 2005 Sumatra earthquake, which generated a much smaller tsunami and less destruction. The damage from the tsunami on Banda Aceh, a town on the island of Sumatra, is shown below.
The earthquake had caused massive movement within the plates, which generated massive ridges near the trench. These ridges then collapsed in places to produce large landslides several miles across. One landslide consisted of a single block of material some 300 feet high and 1.25 miles long. The force of the displaced water was such that individual blocks of rock, massing millions of tons each, were dragged as much as 7 miles across the sea bed. A newly formed oceanic trench several miles wide was also found in the earthquake zone. It is theorized that the landslides and movement of solid material underwater contributed much more to the tsunami than the actual earthquake itself. For example, massive earthquakes have often occurred without a tsunami, but when landslides are involved with the water, tsunamis are almost always generated. A perfect instance of this was during the eruption of Krakatoa. The volcano erupted, and a massive tsunami ensued, killing many on the surrounding islands. The tsunami was not caused by earthquakes, but instead was generated by a massive landslide. Thus, many scientists speculate that the tsunami was generated by a landslide during the Indonesian Earthquake as well. (http://www.newscientist.com/article.ns?id=dn6994)
The earthquake that generated the tsunami was unique, and abnormal in many ways. For example, most earthquakes last only a few seconds to a minute. The Indian Ocean earthquake lasted ten minutes, much longer than normal. This duration caused the entire Earth to vibrate and jolt a few centimeters. Because of this, the earthquake had much more widespread affects than normal. While earthquakes often cause other earthquakes along faults close to the epicenter, the Indian Ocean earthquake caused earthquakes in Alaska, thousands of miles away. (http://www.sciencemag.org/cgi/content/abstract/308/5725/1144). The earthquake also displaced the magma chambers beneath several volcanoes, notably Leuser Mountain, causing it to become active. The Indian Ocean earthquake is also speculated to have played a role in the 2005 Sumatran earthquake, which activated Mount Talang and also sparked activity at the previously dormant Lake Toba supervolcano. This worried many, as the Lake Toba supervolcano was the most recent supereruption in history, and it is hypothesized that the eruption caused a global winter, and also led to many changes in the human race, as the eruption nearly eliminated all humans. Luckily, the volcano hasn't erupted, although it is still being carefully monitored. Also, the earthquake caused the capacity of the Indian Ocean to decrease greatly, resulting in a permanent rise in global sea level of 0.1 millimeters. (http://www.sciencemag.org/cgi/content/full/sci;308/5725/1126) While this sounds like a small amount, it is actually rather large considering the size of the oceans, and the amount of water that must be displaced to generate an overall rise of this size. The earthquake also caused other changes in the Earth's behavior. It caused an oscillation of eight to twelve inches of the Earth's axis, and also shortened Earth's day by an estimated 2.68 microseconds. Luckily, these movements did not affect the Earth much itself, since the Earth naturally deviates slighly from its path, and thus the alterations were finally corrected. However, Earth's crust is estimated to have moved one centimeter upwards, a significant movment that will likely remain. (http://edition.cnn.com/2005/TECH/science/05/19/sumatra.quake/index.html)
The aftermath of the tsunami resulted in many things, besides the destruction. The United Nations, led by the United States, began donating massive amounts of money and supplies to the areas affected by the tsunami. United Nations Secretary General Kofi Annan stated that reconstruction would take between five and ten years, and the world responded. This would signficantly alter global affairs, since many nations banded together to help this effort. One of the main reasons for this was the fear that disease and other factors would lead to the death toll doubling. Also, the United Nations immediately proposed creating a Indian Ocean Tsunami Warning System, and eventually creating a global system to include all parts of the world. While the destruction caused was immense, the tsunami also caused other things. The topography of many areas, particulalry the ocean floor, was changed. Also, the long lost Indian city Mahabalipuram, which had been missing for over 1200 years, was rediscovered after the tsunami washed away much of the sand that had buried it. (http://www.newscientist.com/channel/being-human/mg18524883.800) The tsunami also destroyed many of the mangrove forests, and coral reefs in Indonesia. The salt water poisoned much of the fresh water and crops in Indonesia, much of which will take years to repair. The salt left a layer on top of the arable land in Indonesia, thus rendering it unusable. The loss of fresh water and crops also caused more death, as there was instant starvation and disease. The tsunami ruptured sewage lines, and destroyed the infrastructure of most cities. Disease became rampant, and many authorities predicted that the death toll would double from it. Thankfully, the United Nations and other humanitarian groups rushed aid into the However, the greatest effect was still the loss of human life.
After the tsunamis and earthquakes ceased, the damage was surveyed. 230,000 people had been killed by the tsunami, and billions of dollars worth of property destroyed. Starvation and disease instantly set in, but the effect was minimalized due to many agencies assisting the affected areas. Despite this, chemicals and pollution affected much of the areas hit by the tsunami, rendering long-term problems. Additionally, the long term economy was virtually destroyed, as the tsunami destroyed the vital infrastructure. Small fishing villages lost their boats, docks, and all other buildings in the tsunami, crippling their ability to recover. The land that would previously have been fertile enough to cultivate was covered with a thick layer of sea salt, making it impossible to grow any time of food. Additionally, the tourism industry was virtually destroyed by the tsunami. Not only was the infrastructure gone, with hotels being destroyed, but people also began to fear going to that area of the world, due to the disease and fear of more tsunamis and other related disasters. Thus, the results of the tsunami were not all immediate, instead, the deaths were accompanied by the destruction of much land, agriculture, infrastructure and also the loss of many ecosystems. (http://www.oceansatlas.org/servlet/CDSServlet?status=ND03MTY4NyY2PWVuJjMzPSomMzc9a29z)
The 2004 Indian Ocean earthquake and resulting tsunami were one of the most deadly disasters to ever affect the world. The earthquake devastated the surrounding terrain, and the resulting tsunami killed 230,000 people, with more dying from the aftermath. While the event was not preventable, the damage most likely was, and hopefully it will not happen again. With the steps taken by the United Nations, the damage should be less widespread in future disasters, although the disasters themselves cannot be prevented. It is ironic that despite all the information and technology available, Mother Nature still unleashes devastating events upon the unprepared.
Works Cited
Bilham, Roger. "A Flying Start, Then a Slow Slip". Science Magazine. 20 May 2005. Accessed 2 March 2006. < http://www.sciencemag.org/cgi/content/full/sci;308/5725/1126>
"The Human Toll." UN Office of the Special Envoy for Tsunami Recovery. Accessed 2 March 2006. <http://www.tsunamispecialenvoy.org/country/humantoll.asp>
"Impact of Tsunamis on Ecosystems." UN Atlas of the Oceans. Accessed: March 4, 2006. <http://www.oceansatlas.org/servlet/CDSServlet?status=ND03MTY4NyY2PWVuJjMzPSomMzc9a29z>
Kious, Jacquelyne W. This Dynamic Earth: The Story of Plate Tectonics. Accessed 3 March 2006. <http://pubs.usgs.gov/gip/dynamic/dynamic.html>
Knight, Will. "Asian tsunami seabed pictured with sonar." New Scientist. February 10, 2005. Accessed 2 March 2006. <http://www.newscientist.com/article.ns?id=dn6994>
"Tsunami waves exposed remnants of lost city". New Scientist. February 26, 2005. Accessed 2 March 2006. <http://www.newscientist.com/channel/being-human/mg18524883.800>
Walton, Marsha. "Science and Space". CNN. May 20, 2005. Accessed 4 March 2006. < http://edition.cnn.com/2005/TECH/science/05/19/sumatra.quake/index.html>
West, Michael. "Periodically Triggered Seismicity at Mount Wrangell, Alaska, After the Sumatra Earthquake". Science Magazine. 20 May 2005. Accessed 2 March 2006. <http://www.sciencemag.org/cgi/content/abstract/308/5725/1144>
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