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QHow does tsunami occur?

How does the tsunami ?

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#1wizAnswered at 2013-01-21 14:04:09
Usually, after an earthquake. google .
#2Phat T Answered at 2013-02-14 08:14:09
Happenening Earthquakes in the ocean and then out of that.
#3JerichaAnswered at 2013-04-03 07:28:42
#4Mary BethAnswered at 2013-04-04 17:34:05
earth trembles under water http://earthquake.usgs.gov/eqcenter/eqin ...
#5Ninja :PAnswered at 2013-05-24 22:08:16
jeffy likes apples shimmy!
#6TaraleeAnswered at 2013-06-04 11:29:25
Earth Quake in the sea.
#7@@@@Answered at 2013-06-08 19:49:44
Tsunami occur...when you are not expecting it.

This already been discussed for so long in news papers and current affairs of TV for such a long time after such disaster in Malaysia , Thailand , India etc. world ever faced and you still searching answer? Either you want cross check do people have knowledge or you don't bother to read news papers.
#8Ms. SueAnswered at 2013-06-10 03:58:51
Due to under water earthquakes, volcanoes and landslides.
#9calfAnswered at 2013-07-18 02:19:34
when earthquakes occur under the surface of the earth in the deep oceans ...they create a movement not only in the land but also in the water... there are movements in it and huge waves are formed...that is what we call tsunami...all the best...
#10jo145578Answered at 2013-07-21 01:19:29
"Tsunami " is a Japanese term. "Tidal Wave" occurs more along the Japanese coast due to earthquake prone area.

Try dropping a pebble in bucket full of still water, you observe ripples or waves radiating out. Imagine an explosion (diwali bomb) at the bottom of the bucket full of water - Waves radiate out to the surface. Depending on the power of explosion the scale of the wave varies.

Tsunami is also the same. It is an after affect of some kind of movement beneath the sea. It could be due to underwater Volcanoes, Earthquake or similar happenings.

For more information visit
http://en.wikipedia.org/wiki/Tsunami
#11toriannaAnswered at 2013-07-26 03:09:18
Under water Earthquakes.
#12DaronAnswered at 2013-07-30 20:18:52
could be man induced shock waves by a big explosion,the natural way is a rippling in the earths crust,that produces a subteranian earth quake.
this sets in motion a giant wave that can travel for thousands of miles.

there is also a super tsunami,that is caused by a landslide into the sea from a coastal mountain .
this causes a super tsunami that make the others look insignificant ,of over 20 metres in hight ,that can travel from one side of the Ocean to the other.
thers is a potential situation like this threatening ,the south east American coast ,but it could be hundreds of years before it happens ,but nothing is certain it could also be a lot sooner.
there was one on the east north American coast many years ago and the evidence is still visible
#13ouraclndAnswered at 2013-10-09 09:28:46
Go to howstuffworks.com and type tsunami in the search engine
#14shanequaAnswered at 2013-11-04 17:09:29
Your geography teacher will say that there different plates of earth which keep moving and when two such plates move into each other, it erupts into a tremor or earth quake. Underneath the sea, near Indonesia and Andaman &Nicobar Islands, the crash occured on 24th December, 2004. The collision occured much near the surface of the earth and that too for a pretty long distance, the movement of one plate lading to a the creation of fissure on the surface of earth for a considerable distance resulted in the displacement of a huge chunk of sea water. This literally churned the sea which resulted in strong waves of sea rolling over the coast areas and creating unimaginable amount of damage in its wake.

My religioun belief is that whenever we breach the natural law and moral law, the anger of God or Nature are exptressed in natural calamities. God had ordainined in Bible that he shall destroy the Earth with any more flood. In Hindu religion, also, it is believed that he has put the water in the sea and forbade the sea from crossing over the coastal line. He has enjoined 'Agni' to remain in the midst of the sea to check and control the sea. It is my belief that when man crosses all limits of morality, Nature some times cross the Lakshman rekha, to impress upon him the need for remaining within the ordained bounds.
#15maribelAnswered at 2013-11-06 00:19:50
A tsunami (pronounced /tsʊˈnɑːmi/ or /sʊˈnɑːmi/) is a series of waves when a body of water, such as an ocean is rapidly displaced on a massive scale. Earthquakes, mass movements above or below water, volcanic eruptions and other underwater explosions, and large meteorite impacts all have the potential to generate a tsunami. The effects of a tsunami can range from unnoticeable to devastating.

The term tsunami comes from the Japanese language meaning harbour ("tsu", 津) and wave ("nami", 波). Although in Japanese tsunami is used for both the singular and plural, in English tsunamis is often used as the plural. The term was created by fishermen who returned to port to find the area surrounding their harbour devastated, although they had not been aware of any wave in the open water. Tsunamis are common throughout Japanese history, as 195 events in Japan have been recorded.

A tsunami has a much smaller amplitude (wave heights) offshore, and a very long wavelength (often hundreds of kilometres long), which is why they generally pass unnoticed at sea, forming only a passing "hump" in the ocean.

Tsunamis have been historically referred to as tidal waves because as they approach land, they take on the characteristics of a violent onrushing tide rather than the sort of cresting waves that are formed by wind action upon the ocean (with which people are more familiar). Since they are not actually related to tides the term is considered misleading and its usage discouraged by oceanographers. [1] However, since not all tsunamis occur in harbours, that term is equally misleading, although it does have the benefit of being misleading in a different language.

Causes
Generation of a tsunami
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Generation of a tsunami

Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Such large vertical movements of the Earth’s crust can occur at plate boundaries. Subduction earthquakes are particularly effective in generating tsunamis. As an Oceanic Plate is subducted beneath a Continental Plate, it sometimes brings down the lip of the Continental with it. Eventually, too much stress is put on the lip and it snaps back, sending shockwaves through the Earth’s crust, causing a tremor under the sea, known as an Undersea Earthquake.

Sub-marine landslides (which are sometimes triggered by large earthquakes) as well as collapses of volcanic edifices may also disturb the overlying water column as sediment and rocks slide downslope and are redistributed across the sea floor. Similarly, a violent submarine volcanic eruption can uplift the water column and form a tsunami.

Tsunamis are surface gravity waves that are formed as the displaced water mass moves under the influence of gravity and radiate across the ocean like ripples on a pond.

In the 1950s it was discovered that larger tsunamis than previously believed possible could be caused by landslides, explosive volcanic action and impact events. These phenomena rapidly displace large volumes of water, as energy from falling debris or expansion is transferred to the water into which the debris falls. Tsunamis caused by these mechanisms, unlike the ocean-wide tsunamis caused by some earthquakes, generally dissipate quickly and rarely affect coastlines distant from the source due to the small area of sea affected. These events can give rise to much larger local shock waves (solitons), such as the landslide at the head of Lituya Bay which produced a water wave estimated at 50 – 150 m and reached 524 m up local mountains. However, an extremely large landslide could generate a megatsunami that might have ocean-wide impacts.

[edit] Characteristics
There is a common misconception that tsunamis behave like wind-driven waves or swells (with air behind them, as in this celebrated 19th century woodcut by Hokusai). In fact, a tsunami is better understood as a new and suddenly higher sea level, which manifests as a shelf or shelves of water. The leading edge of a tsunami superficially resembles a breaking wave but behaves differently: the rapid rise in sea level, combined with the weight and pressure of the ocean behind it, has far greater force.
Enlarge
There is a common misconception that tsunamis behave like wind-driven waves or swells (with air behind them, as in this celebrated 19th century woodcut by Hokusai). In fact, a tsunami is better understood as a new and suddenly higher sea level, which manifests as a shelf or shelves of water. The leading edge of a tsunami superficially resembles a breaking wave but behaves differently: the rapid rise in sea level, combined with the weight and pressure of the ocean behind it, has far greater force.

Often referred to as "tidal waves", a tsunami does not look like the popular impression of "a normal wave only much bigger". Instead it looks rather like an endlessly onrushing tide which forces its way around and through any obstacle. Most of the damage is caused by the huge mass of water behind the initial wave front, as the height of the sea keeps rising fast and floods powerfully into the coastal area. The sheer weight of water is enough to pulverise objects in its path, often reducing buildings to their foundations and scouring exposed ground to the bedrock. Large objects such as ships and boulders can be carried several miles inland before the tsunami subsides.

Tsunamis act very differently from typical surf swells: they contain immense energy, propagate at high speeds and can travel great trans-oceanic distances with little overall energy loss. A tsunami can cause damage thousands of kilometres from its origin, so there may be several hours between its creation and its impact on a coast, arriving long after the seismic wave generated by the originating event arrives. Although the total or overall loss of energy is small, the total energy is spread over a larger and larger circumference as the wave travels. The energy per linear metre in the wave is proportional to the inverse of the distance from the source.[citation needed] (In other words, it decreases linearly with distance.) This is the two-dimensional equivalent of the inverse square law, which is followed by waves which propagate in three dimensions (in a sphere instead of a circle).

A single tsunami event may involve a series of waves of varying heights; so the set of waves is called a train. In open water, tsunamis have extremely long periods (the time for the next wave top to pass a point after the previous one), from minutes to hours, and long wavelengths of up to several hundred kilometres. This is very different from typical wind-generated swells on the ocean, which might have a period of about 10 seconds and a wavelength of 150 metres.

The height of a tsunami wave in open water is often less than one metre, and the height is spread over the wavelength of the tsunami which is multiple kilometres. This is unnoticeable to people on ships in deep water. Because it has such a large wavelength, the energy of a tsunami mobilizes the entire water column down to the sea bed. Typical ocean surface waves in deep water cause water motion to a depth equal to half their wavelength. This means, ocean surface wave motion will only reach down to a depth of a few 100 m or less. Tsunamis, by contrast behave as 'shallow water waves' in the deep ocean.

Because a Tsunami behaves like a 'shallow water wave,' its speed is based on the depth of the water. Typically, a tsunami wave will travel across a deep ocean at an average speed of 400 to 500 mph.([2]). As the wave approaches land, the sea shallows and the tsunami wave no longer travels as quickly, so it begins to 'pile-up'; the wave-front becomes steeper and taller, and there is less distance between crests. While a person at the surface of deep water would probably not even notice the tsunami, the wave can increase to a height of six stories or more as it approaches the coastline and compresses. The steepening process is analogous to the cracking of a tapered whip. As a wave goes down the whip from handle to tip, the same energy is deposited in less and less material, which then moves more violently as it receives this energy.

A wave becomes a 'shallow-water wave' when the ratio between the water depth and its wavelength gets very small, and since a tsunami has an extremely large wavelength (hundreds of kilometres), tsunamis act as a shallow-water wave even in deep oceanic water. Shallow-water waves move at a speed that is equal to the square root of the product of the acceleration of gravity (9.8 m/s2) and the water depth. For example, in the Pacific Ocean, where the typical water depth is about 4000 m, a tsunami travels at about 200 m/s (720 km/h or 450 mi/h) with little energy loss, even over long distances. At a water depth of 40 m, the speed would be 20 m/s (about 72 km/h or 45 mi/h), which is much slower than the speed in the open ocean but the wave would still be difficult to outrun.

Tsunamis propagate outward from their source, so coasts in the "shadow" of affected land masses are usually fairly safe. However, tsunami waves can diffract around land masses (as shown in this Indian Ocean tsunami animation as the waves reach southern Sri Lanka and India). It's also not necessary that they are symmetrical; tsunami waves may be much stronger in one direction than another, depending on the nature of the source and the surrounding geography.

Local geographic peculiarities can lead to seiche or standing waves forming, which can amplify the onshore damage. For instance, the tsunami that hit Hawaii on April 1, 1946 had a fifteen-minute interval between wave fronts. The natural resonant period of Hilo Bay is about thirty minutes. That meant that every second wave was in phase with the motion of Hilo Bay, creating a seiche in the bay. As a result, Hilo suffered worse damage than any other place in Hawaii, with the tsunami/seiche reaching a height of 14 m and killing 159 inhabitants.

[edit] Tsunami wave

Ocean waves are normally divided into 3 groups, characterized by depth:

* Deep water
* Intermediate water
* Shallow water

Even though a tsunami is generated in deep water (around 4000 m below mean sea level), tsunami waves are considered shallow-water waves. As the tsunami wave approaches the shallow waters of shore, its time period remains the same, but its wavelength decreases rapidly, thus causing the water to pile up to form tremendous crests, in an effect known as "shoaling".

[edit] Signs of an approaching tsunami

The following have at various times been associated with a tsunami [3]:

* An earthquake may be felt.
* Large quantities of gas may bubble to the water surface and make the sea look as if it is boiling.
* The water in the waves may be unusually hot.
* The water may smell of rotten eggs (hydrogen sulfide) or of petrol or oil.
* The water may sting the skin.
* A thunderous boom may be heard followed by
o a roaring noise as of a jet plane
o or a noise akin to the periodic whop-whop of a helicopter,
o or a whistling sound.
* The sea may recede to a considerable distance.
* A flash of red light might be seen near the horizon.

[edit] Warnings and prevention
"Tsunami Hazard Zone" sign at the University of California, Santa Barbara
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"Tsunami Hazard Zone" sign at the University of California, Santa Barbara
Tsunami wall at Tsu-shi, Japan
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Tsunami wall at Tsu-shi, Japan

Tsunamis cannot be prevented or precisely predicted, but there are some warning signs of an impending tsunami, and there are many systems being developed and in use to reduce the damage from tsunamis.

In instances where the leading edge of the tsunami wave is its trough, the sea will recede from the coast half of the wave's period before the wave's arrival. If the slope is shallow, this recession can exceed many hundreds of metres. People unaware of the danger may remain at the shore due to curiosity, or for collecting fish from the exposed sea bed.
Tsunami warning sign on seawall in Kamakura, Japan, 2004. In the Muromachi period, a tsunami struck Kamakura, destroying the wooden building that housed the colossal statue of Amida Buddha at Kotokuin. Since that time, the statue has been outdoors.
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Tsunami warning sign on seawall in Kamakura, Japan, 2004. In the Muromachi period, a tsunami struck Kamakura, destroying the wooden building that housed the colossal statue of Amida Buddha at Kotokuin. Since that time, the statue has been outdoors.

In instances where the leading edge of the tsunami is its first peak, succeeding waves can lead to further flooding. Again, being educated about a tsunami is important, to realize that when the water level drops the first time, the danger is not yet over. In a low-lying coastal area, a strong earthquake is a major warning sign that a tsunami may be produced.

Regions with a high risk of tsunamis may use tsunami warning systems to detect tsunamis and warn the general population before the wave reaches land. In some communities on the west coast of the United States, which is prone to Pacific Ocean tsunamis, warning signs advise people where to run in the event of an incoming tsunami. Computer models can roughly predict tsunami arrival and impact based on information about the event that triggered it and the shape of the seafloor (bathymetry) and coastal land (topography). [4]

One of the early warnings comes from nearby animals. Many animals sense danger and flee to higher ground before the water arrives. The Lisbon quake is the first documented case of such a phenomenon in Europe. The phenomenon was also noted in Sri Lanka in the 2004 Indian Ocean earthquake. [5] Some scientists speculate that animals may have an ability to sense subsonic Rayleigh waves from an earthquake minutes or hours before a tsunami strikes shore (Kenneally, [6]).

While it is not possible to prevent a tsunami, in some particularly tsunami-prone countries some measures have been taken to reduce the damage caused on shore. Japan has implemented an extensive programme of building tsunami walls of up to 4.5 m (13.5 ft) high in front of populated coastal areas. Other localities have built floodgates and channels to redirect the water from incoming tsunamis. However, their effectiveness has been questioned, as tsunamis are often higher than the barriers. For instance, the tsunami which hit the island of Hokkaido on July 12, 1993 created waves as much as 30 m (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.

The effects of a tsunami can be mitigated by natural factors such as tree cover on the shoreline. Some locations in the path of the 2004 Indian Ocean tsunami escaped almost unscathed as a result of the tsunami's energy being sapped by a belt of trees such as coconut palms and mangroves. In one striking example, the village of Naluvedapathy in India's Tamil Nadu region suffered minimal damage and few deaths as the wave broke up on a forest of 80,244 trees planted along the shoreline in 2002 in a bid to enter the Guinness Book of Records. [7] Environmentalists have suggested tree planting along stretches of sea coast which are prone to tsunami risks. While it would take some years for the trees to grow to a useful size, such plantations could offer a much cheaper and longer-lasting means of tsunami mitigation than the costly and environmentally destructive method of erecting artificial barriers.
#16carolynAnswered at 2013-12-06 19:19:50
When there is a eathquake in the sea then Tsunami occurs
#17Joseph B.Answered at 2013-12-25 15:30:01
earth quake on ocean floor causing ripples in forms of big and speedy waves.
#18VitaAnswered at 2014-01-11 19:48:52
Tsunamis occur due to underwater earthquakes, landslides or volcanic eruptions. Tsunamis travel at speeds ranging from 80-300 miles/hr. They may acheive upto 30 ft. The sea near the shore recedes, exposing tthe ocean floor. This is a natural tsunami warning. :D:D
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