A tsunami ('harbor wave') or tidal wave is a series of water waves (called a tsunami wave train) caused by the displacement of a large volume of a body of water, usually an ocean, but can occur in large lakes. Tsunamis are a frequent occurrence in Japan; approximately 195 events have been recorded. Due to the immense volumes of water and energy involved, tsunamis can devastate coastal regions.
Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), landslides and other mass movements, meteorite ocean impacts or similar impact events, and other disturbances above or below water all have the potential to generate a tsunami. The Greek historian Thucydides was the first to relate tsunami to submarine earthquakes, but understanding of tsunami's nature remained slim until the 20th century and is the subject of ongoing research. Many early geological, geographical, and oceanographic texts refer to tsunamis as "seismic sea waves. CHARACTERISTICS: While everyday wind waves have a wavelength (from crest to crest) of about 100 meters (330 ft) and a height of roughly 2 meters (6. 6 ft), a tsunami in the deep ocean has a wavelength of about 200 kilometers (120 mi). Such a wave travels at well over 800 kilometers per hour (500 mph), but due to the enormous wavelength the wave oscillation at any given point takes 20 or 30 minutes to complete a cycle and has amplitude of only about 1 meter (3. 3 ft). This makes tsunamis difficult to detect over deep water. Ships rarely notice their passage.
As the tsunami approaches the coast and the waters become shallow, wave shoaling compresses the wave and its velocity slows below 80 kilometers per hour (50 mph). Its wavelength diminishes to less than 20 kilometers (12 mi) and its amplitude grows enormously, producing a distinctly visible wave. Since the wave still has such a long wavelength, the tsunami may take minutes to reach full height. Except for the very largest tsunamis, the approaching wave does not break (like a surf break), but rather appears like a fast moving tidal bore.
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Open bays and coastlines adjacent to very deep water may shape the tsunami further into a step-like wave with a steep-breaking front. When the tsunami's wave peak reaches the shore, the resulting temporary rise in sea level is termed 'run up'. Run up is measured in meters above a reference sea level. A large tsunami may feature multiple waves arriving over a period of hours, with significant time between the wave crests. The first wave to reach the shore may not have the highest run up. About 80% of tsunamis occur in the Pacific Ocean, but are possible wherever there are large bodies of water, including lakes.
They are caused by earthquakes, landslides, volcanic explosions, and bolides. GENERATION MECHANISMS: The principal generation mechanism (or cause) of a tsunami is the displacement of a substantial volume of water or perturbation of the sea. This displacement of water is usually attributed to earthquakes, landslides, volcanic eruptions, or more rarely by meteorites and nuclear tests. The waves formed in this way are then sustained by gravity. It is important to note that tides do not play any part in the generation of tsunamis; hence referring to tsunamis as 'tidal waves' is inaccurate.
Seismicity generated tsunamis Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquake that are associated with the earth's crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. More specifically, a tsunami can be generated when thrust faults associated with convergent or destructive plate boundaries move abruptly, resulting in water displacement, due to the vertical component of movement involved.
Movement on normal faults will also cause displacement of the seabed, but the size of the largest of such events is normally too small to give rise to a significant tsunami. |[pic] |[pic] |[pic] |[pic] | |Drawing of tectonic plate |Overriding plate bulges under |Plate slips, causing |The energy released produces | |boundary before earthquake. |strain, causing tectonic uplift. |subsidence and releasing energy |tsunami waves. | | | |into water. | Tsunamis have a small amplitude (wave height) offshore, and a very long wavelength (often hundreds of kilometers long), which is why they generally pass unnoticed at sea, forming only a slight swell usually about 300 millimeters (12 in) above the normal sea surface. They grow in height when they reach shallower water, in a wave shoaling process described below. A tsunami can occur in any tidal state and even at low tide can still inundate coastal areas. On April 1, 1946, a magnitude-7. 8 (Richter scale) earthquake occurred near the Aleutian Islands, Alaska.
It generated a tsunami which inundated Hilo on the island of Hawaii’s with a 14 meters (46 ft) high surge. The area where the earthquake occurred is where the Pacific Ocean floor is subducting (or being pushed downwards) under Alaska. Examples of tsunami at locations away from convergent boundaries include Storegga about 8,000 years ago, Grand Banks 1929, Papua New Guinea 1998 (Tappin, 2001). The Grand Banks and Papua New Guinea tsunamis came from earthquakes which destabilized sediments, causing them to flow into the ocean and generate a tsunami. They dissipated before traveling transoceanic distances.
The cause of the Storegga sediment failure is unknown. Possibilities include an overloading of the sediments, an earthquake or a release of gas hydrates (methane etc. ) The 1960 Valdivia earthquake (Mw 9. 5) (19:11 hrs UTC), 1964 Alaska earthquake (Mw 9. 2), and 2004 Indian Ocean earthquake (Mw 9. 2) (00:58:53 UTC) are recent examples of powerful mega thrust earthquakes that generated tsunamis (known as teletsunamis) that can cross entire oceans. Smaller (Mw 4. 2) earthquakes in Japan can trigger tsunamis (called local and regional tsunamis) that can only devastate nearby coasts, but can do so in only a few minutes.
In the 1950s, it was discovered that larger tsunamis than had previously been believed possible could be caused by giant landslides. These phenomena rapidly displace large water volumes, as energy from falling debris or expansion transfers to the water at a rate faster than the water can absorb. Their existence was confirmed in 1958, when a giant landslide in Lituya Bay, Alaska, caused the highest wave ever recorded, which had a height of 524 meters (over 1700 feet). The wave didn't travel far, as it struck land almost immediately. Two people fishing in the bay were killed, but another boat amazingly managed to ride the wave.
Scientists named these waves mega tsunami. Scientists discovered that extremely large landslides from volcanic island collapses can generate mega tsunami that can travel trans-oceanic distances. SCALES OF INTENSITY AND MAGNITUDE: As with earthquakes, several attempts have been made to set up scales of tsunami intensity or magnitude to allow comparison between different events. Intensity scales The first scales used routinely to measure the intensity of tsunami were the Sieberg-Ambraseys scale, used in the Mediterranean Sea and the Imamura-Iida intensity scale, used in the Pacific Ocean.
The latter scale was modified by Soloviev, who calculated the Tsunami intensity I according to the formula [pic] Where Hav is the average wave height along the nearest coast. This scale, known as the Soloviev-Imamura tsunami intensity scale, is used in the global tsunami catalogues compiled by the NGDC/NOAA and the Novosibirsk Tsunami Laboratory as the main parameter for the size of the tsunami. Magnitude scales The first scale that genuinely calculated a magnitude for a tsunami, rather than an intensity at a particular location was the ML scale proposed by Murty & Loomis based on the potential energy.
Difficulties in calculating the potential energy of the tsunami mean that this scale is rarely used. Abe introduced the tsunami magnitude scale Mt, calculated from, [pic] where h is the maximum tsunami-wave amplitude (in m) measured by a tide gauge at a distance R from the epicenter, a, b & D are constants used to make the Mt scale match as closely as possible with the moment magnitude scale. WARNINGS AND PREDICTIONS: Drawbacks can serve as a brief warning. People who observe drawback (many survivors report an accompanying sucking sound), can survive only if they immediately run for high ground or seek the upper floors of nearby buildings.
In 2004, ten-year old Tilly Smith of Surrey, England, was on Maikhao beach in Phuket, Thailand with her parents and sister, and having learned about tsunamis recently in school, told her family that a tsunami might be imminent. Her parents warned others minutes before the wave arrived, saving dozens of lives. She credited her geography teacher, Andrew Kearney. In the 2004 Indian Ocean tsunami drawback was not reported on the African coast or any other eastern coasts it reached. This was because the wave moved downwards on the eastern side of the fault line and upwards on the western side.
The western pulse hit coastal Africa and other western areas. A tsunami cannot be precisely predicted, even if the magnitude and location of an earthquake is known. Geologists, oceanographers, and seismologists analyze each earthquake and based on many factors may or may not issue a tsunami warning. However, there are some warning signs of an impending tsunami, and automated systems can provide warnings immediately after an earthquake in time to save lives. One of the most successful systems uses bottom pressure sensors that are attached to buoys. The sensors constantly monitor the pressure of the overlying water column.
This is deduced through the calculation: [pic] Where, P = the overlying pressure in Newton per meter square, ? = the density of the seawater = 1. 1 x 103 kg/m3, g = the acceleration due to gravity = 9. 8 m/s2 and h = the height of the water column in meters. Hence for a water column of 5,000 m depth the overlying pressure is equal to [pic] Or about 5500 tonnes-force per square meter. Regions with a high tsunami risk typically use tsunami warning systems to warn the population before the wave reaches land. On the west coast of the United States, which is prone to Pacific Ocean tsunami, warning signs indicate evacuation routes.
In Japan, the community is well-educated about earthquakes and tsunamis, and along the Japanese shorelines the tsunami warning signs are reminders of the natural hazards together with a network of warning sirens, typically at the top of the cliff of surroundings hills. The Pacific Tsunami Warning System is based in Honolulu, Hawaii. It monitors Pacific Ocean seismic activity. A sufficiently large earthquake magnitude and other information trigger a tsunami warning. While the seduction zones around the Pacific are seismically active, not all earthquakes generate tsunami.
Computers assist in analyzing the tsunami risk of every earthquake that occurs in the Pacific Ocean and the adjoining land masses. |[pic] |[pic] |[pic] |[pic] | |Tsunami hazard sign |A tsunami warning sign on |The monument to the victims of |Tsunami memorial | |atBamfield, British Columbia |a seawall in Kamakura, Japan, |tsunami at Laupahoehoe, Hawaii |inKanyakumari beach | | |2004. | | |
As a direct result of the Indian Ocean tsunami, a re-appraisal of the tsunami threat for all coastal areas is being undertaken by national governments and the United Nations Disaster Mitigation Committee. A tsunami warning system is being installed in the Indian Ocean. Computer models can predict tsunami arrival, usually within minutes of the arrival time. Bottom pressure sensors relay information in real time. Based on these pressure readings and other seismic information and the seafloor's shape and coastal topography, the models estimate the amplitude and surge height of the approaching tsunami.
All Pacific Rim countries collaborate in the Tsunami Warning System and most regularly practice evacuation and other procedures. In Japan, such preparation is mandatory for government, local authorities, emergency services and the population. Some zoologists hypothesize that some animal species have an ability to sense subsonic Rayleigh waves from an earthquake or a tsunami. If correct, monitoring their behavior could provide advance warning of earthquakes, tsunami etc. However, the evidence is controversial and is not widely accepted.
There are unsubstantiated claims about the Lisbon quake that some animals escaped to higher ground, while many other animals in the same areas drowned. The phenomenon was also noted by media sources in Sri Lanka in the 2004 Indian Ocean earthquake.  It is possible that certain animals (e. g. , elephants) may have heard the sounds of the tsunami as it approached the coast. The elephants' reaction was to move away from the approaching noise. By contrast, some humans went to the shore to investigate and many drowned as a result. It is not possible to prevent a tsunami.
However, in some tsunami-prone countries some earthquake engineering measures have been taken to reduce the damage caused on shore. Japan built many tsunami walls of up to 4. 5 metres (15 ft) to protect populated coastal areas. Other localities have built floodgates and channels to redirect the water from incoming tsunami. However, their effectiveness has been questioned, as tsunami often overtop the barriers. For instance, the Okushiri, Hokkaido tsunami which struck Okushiri Island of Hokkaido within two to five minutes of the earthquake on July 12, 1993 created waves as much as 30 metres (100 ft) tall—as high as a 10-story building.
The port town of Aonae was completely surrounded by a tsunami wall, but the waves washed right over the wall and destroyed all the wood-framed structures in the area. The wall may have succeeded in slowing down and moderating the height of the tsunami, but it did not prevent major destruction and loss of life.  Natural factors such as shoreline tree cover can mitigate tsunami effects. Some locations in the path of the 2004 Indian Ocean tsunami escaped almost unscathed because trees such as coconut palms and mangroves absorbed the tsunami's energy.
In one striking example, the village of Naluvedapathy in India's Tamil Nadu region suffered only minimal damage and few deaths because the wave broke against a forest of 80,244 trees planted along the shoreline in 2002 in a bid to enter the Guinness Book of Records.  Environmentalists have suggested tree planting along tsunami-prone seacoasts. Trees require years to grow to a useful size, but such plantations could offer a much cheaper and longer-lasting means of tsunami mitigation than artificial barriers. The Love Canal chemical waste dump
In 1920 Hooker Chemical had turned an area in Niagara Falls into a municipal and chemical disposal site. In 1953 the site was filled and relatively modern methods were applied to cover it. A thick layer of impermeable red clay sealed the dump, preventing chemicals from leaking out of the landfill. A city near the dumpsite wanted to buy it for urban expansion. Despite the warnings of Hooker the city eventually bought the site for the meager amount of 1 dollar. Hooker could not sell for more, because they did not want to earn money off a project so clearly unwise.
The city began to dig to develop a sewer, damaging the red clay cap that covered the dumpsite below. Blocks of homes and a school were built and the neighborhood was named Love Canal. Love Canal seemed like a regular neighborhood. The only thing that distinguished this neighborhood from other was the strange odors that often hung in the air and an unusual seepage noticed by inhabitants in their basements and yards. Children in the neighborhood often fell ill. Love Canal families regularly experienced miscarriages and birth defects.
Lois Gibbs, an activist, noticed the high occurrence of illness and birth defects in the area and started documenting it. In 1978 newspapers revealed the existence of the chemical waste dump in the Love Canal area and Lois Gibbs started petitioning for closing the school. In August 1978, the claim succeeded and the NYS Health Department ordered closing of the school when a child suffered from chemical poisoning. When Love Canal was researched over 130 pounds of the highly toxic carcinogenic TCDD, a form of dioxin, was discovered. The total of 20. 00 tons of waste present in the landfill appeared to contain more than 248 different species of chemicals. The waste mainly consisted of pesticide residues and chemical weapons research refuse. The chemicals had entered homes, sewers, yards and creeks and Gibbs decided it was time for the more than 900 families to be moved away from the location. Eventually President Carter provided funds to move all the families to a safer area. Hooker’s parent company was sued and settled for 20 million dollars. Despite protests by Gibbs’s organization some of the houses in Love Canal went up for sale some 20 years later.
The majority of the houses are on the market now and the neighborhood may become inhabited again after 20 years of abandonment. The houses in Love Canal are hard to sell, despite a renaming of the neighborhood. It suffered such a bad reputation after the incident that banks refused mortgages on the houses. None of the chemicals have been removed from the dumpsite. It has been resealed and the surrounding area was cleaned and declared safe. Hooker’s mother company paid an additional 230 million dollars to finance this cleanup. They are now responsible for the management of the dumpsite.
Today, the Love Canal dumpsite is known as one of the major environmental disasters of the century. **** Love Canal is an abandoned canal in Niagara County, New York, where a huge amount of toxic waste was buried. The waste was composed of at least 300 different chemicals, totaling an estimated 20,000 metric tons. The existence of the waste was discovered in the 1970s when families living in homes subsequently built next to the site found chemical wastes seeping up through the ground into their basements, forcing them to eventually abandon their homes.
Love Canal was used from the 1940s through the 1950s by the Hooker Chemical Company and the city of Niagara Falls, among others, to dispose of their hazardous and municipal wastes and other refuse. The canal was surrounded by clay and was thought at the time to be a safe place for disposal—and, in fact, burying chemicals in the canal was probably safer than many other methods and sites used for chemical disposal at the time. In 1953, the Niagara Falls Board of Education bought the land-fill for $1 and constructed an elementary school with playing fields on the site.
Roads and sewer lines were added and, in the early 1970s, single-family homes were built adjacent to the site. Following a couple of heavy rains in the mid-1970s, the canal flooded and chemicals were observed on the surface of the site and in the basements of houses abutting the site. Newspaper coverage, investigations by the State of New York and by the U. S. Environmental Protection Agency, combined with pressure from the district's U. S. congressional representative and outrage on the part of local residents, led to the declaration of a health emergency involving "great and imminent peril to the health of the general public. Ultimately, in August, 1978, a decision was made by Governor Hugh Carey, supported by the White House, to evacuate the residents and purchase 240 homes surrounding the site. Shortly thereafter, the residents of nearby homes that did not immediately abut the site also became concerned about their health and conducted a health survey that purported to show an increase in the occurrence of various diseases and problems such as birth defects and miscarriages, which were attributed to chemical exposures.
A great controversy ensued over whether the observations were real or reflected normal rates of such problems, and whether chemical exposures had, in fact, occurred. Eventually, political pressure resulted in families being given an opportunity to leave and have their homes purchased by the State. About 70 homes remained occupied in 1989 by families who chose not to move. The controversy at Love Canal followed on the heels of the heightened awareness that occurred in the 1960s about environmental contamination, and it contributed to public and regulatory concern about hazardous wastes, waste disposal, and disclosure of such practices.
Such concerns led Congress to pass the Resource Conservation and Recovery Act (RCRA) and the Toxic Substances Control Act (TSCA) in 1976, and the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), also known as the Superfund bill, in 1980. When CERCLA was passed, few were aware of the extent of the problem potentially created by years of inappropriate or inadequate hazardous waste disposal practices. Since implementing CERCLA, the U. S.
Environmental Protection Agency has identified more than 40,000 potentially contaminated "Superfund" sites. The Gulf War In August 1990 Iraqi forces invaded Kuwait, starting the Gulf War in which an allegiance of 34 nations worldwide was involved. In January 1991 of the Gulf War, Iraqi forces committed two environmental disasters. The first was a major oil spill 16 kilometers off the shore of Kuwait by dumping oil from several tankers and opening the valves of an offshore terminal. The second was the setting fire to 650 oil wells in Kuwait.
The apparent strategic goal of the action was to prevent a potential landing by US Marines. American air strikes on January 26 destroyed pipelines to prevent further spillage into the Gulf. This however seemed to make little difference. Approximately one million tons of crude oil was already lost to the environment, making this the largest oil spill of human history. In the spring of 1991, as many as 500 oil wells were still burning and the last oil well was not extinguished until a few months later, in November.
The oil spills did considerable damage to life in the Persian Gulf (see picture). Several months after the spill, the poisoned waters killed 20. 000 seabirds and had caused severe damage to local marine flora and fauna. The fires in the oil wells caused immense amounts of soot and toxic fumes to enter the atmosphere. This had great effects on the health of the local population and biota for several years. The pollution also had a possible impact on local weather patterns.
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