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Vertical movement of the ocean floor will raise or lower the water above it, causing waves that move outward. Almost undetectable in the deep ocean, tsunamis rise to a mighty crest as the ocean shallows.The intensity at which a tsunami strikes land is also related to the distance between the land and the center of the earthquake. It's here, at the epicenter, that the tsunami originates. As the waves spread from the epicenter in the typical arc-shaped pattern, their energy also spreads out, making tsunamis usually most dangerous to those closest the epicenter.
Spread out, but still powerful
One factor that distinguishes tsunamis from small, familiar waves is their extremely long wavelength. On the open ocean, the peaks of neighboring waves in a tsunami may be 300 kilometers -- you read that right: 300 kilometers! -- apart.
Even in the deepest ocean, that wavelength makes tsunamis what scientists call "shallow water waves." The speed of a shallow-water wave depends on the water depth, and in deep water, tsunamis can move at 500 to 600 miles per hour. That gives them the ability to keep pace with a Boeing 747, yet even after crossing the entire Pacific Ocean, the waves retain huge amounts of energy.
But you wouldn't see a tsunami from the cockpit of a 747. A killer tsunami may be only 2 feet tall in mid-ocean -- far too small to be noticed from an airplane or even a ship.
How can all that destructive kinetic energy hide in waves that we can barely see? Because waves are far more than what you can see on the surface -- they also include the nearly circular movement of water below the surface. Because long-wavelength waves extend far deeper into the water than waves with peaks closer together, there's a massive amount of water in motion beneath the surface. That's where these practically invisible waves store an enormous amount of energy.
As we've indicated, boats in deep water ride over the worst tsunamis without even noticing them. It's only when they reach shallow water and "run aground" that these waves become intense and dangerous. Like all shallow water waves, tsunamis slow when the lower part of the wave -- where the water is moving in a circle -- encounters the bottom as the ocean floor slopes up toward land.
But while the front of the wave slows, the wave behind is still moving rapidly, causing a giant pile-up at the front. Then the kinetic energy that was spread through the entire depth of the ocean becomes concentrated in a towering wave at the surface.
It is these surface waves -- which can be 10 meters high or taller as they cross the beach -- that cause the utter destruction of tsunamis. Usually, a series of waves, often as much as an hour apart, come crashing in -- killing those who return to help victims of the previous waves.
25 MAY 2008
Tsunamis are obviously waves and as such they follow the fundamentals of waves. These basics are as follows:
The wavelength is the length from crest to crest, and the amplitude is the distance from the bottom of the trough to the top of the crest. The period is the length of time for one crest to travel the distance to where the other crest was.
A vertical displacement in the water column at sea creates waves that become tsunamis. While at sea these waves have a VERY large wavelength (approximently 500 kilometers), but their overall amplitude is very small (about a meter). In the ocean, a tsunami could pass beneath the boat that you are on and you would hardly notice it! Because of the very large wavelength, the wave loses very little energy as it moves along the ocean, thus allowing tsunamis to inflict damage hundreds of miles away. As these waves approach the shore, they start to behave differently (like shallow water waves instead of deep water waves) and their wavelength becomes smaller and the amplitude becomes much taller.
[http://www.ew.govt.nz/enviroinfo/hazards/
naturalhazards/coastal/tsunami.htm]
The picture above clearly illustrates the wavelength becoming smaller and the amplitude rising suddenly.
The position of a wave is defined as x(t) = A cos(ωt + φ) where A is the amplitude, ω is the period, and φ is the phase constant.
The velocity of a tsunami is dependant on only one factor: the depth of the ocean over which it is traveling. The maximum velocity of a tsunami can be up to 800 kilometers an hour.
Thus the velocity is equal to the square root of g (gravitational constant 9.81 m / s^2) times the average depth of the ocean. This method was used estimate the average depth of the ocean between Hawaii and Alaska in 1856 before the advent of sonar and modern depth techniques. The scientists knew the amount of time it took for the tsunami to reach Hawaii from Alaska, and also the distance, so they thus knew the velocity. Since g is already known, they simply solved for the average ocean depth.
Another factor in the creation of tsunamis is the depth of the earthquake. If the earthquake occurs more than 100 km below the surface, a tsunami will not occur because there is not enough vertical displacement of the water.
[http://pubs.usgs.gov/circ/c1187/]
These images show how the tectonic plates collide creating an earthquake and a vertical displacement in the water.
[http://www.pmel.noaa.gov/tsunami/Iugg99/iugg99_titlepage.html]
As can be clearly seen from the picture above, tsunamis extend radially from the source of the earthquake, much as if a pebble had been thrown into a pond.
If you have adiquate bandwidth watch this animation of a tsunami spreading across the Pacific (several Mb) http://www.pmel.noaa.gov/tsunami/Mov/andr1.mov
The 2004 Indian Ocean earthquake was an undersea (subduction) earthquake that occurred at 00:58:53 UTC on December 26, 2004, with an epicentre off the west coast of Sumatra, Indonesia. The earthquake triggered a series of devastating tsunamis along the coasts of most landmasses bordering the Indian Ocean, killing more than 225,000 people in eleven countries, and inundating coastal communities with waves up to 30 meters (100 feet). It was one of the deadliest natural disasters in history. Indonesia, Sri Lanka, India, and Thailand were hardest hit.
With a magnitude of between 9.1 and 9.3, it is the second largest earthquake ever recorded on a seismograph. This earthquake had the longest duration of faulting ever observed, between 8.3 and 10 minutes. It caused the entire planet to vibrate as much as 1 cm (0.5 inches)and triggered other earthquakes as far away as Alaska. The disaster is known by the scientific community as the Great Sumatra-Andaman earthquake, and is also known as the Asian Tsunami and the Boxing Day Tsunami. The tsunami occurred exactly one year after the 2003 Bam earthquake and exactly two years before the 2006 Hengchun earthquake.
The plight of the many affected people and countries prompted a widespread humanitarian response. In all, the worldwide community donated more than $7 billion (2004 U.S. dollars) in humanitarian aid.
BY JINNY
13 May 2008
08 May 2008
Tsunami threatening to drown the unwary
Krakatoa Volcano in IndonesiaOn the open ocean, tsunami waves approach speeds of 500 mph, almost fast enough to keep pace with a jetliner. But gazing out the window of a 747, you wouldn't be able to pick it out from the wind-driven swells. In deep water, the waves spread out and hunch down, with hundreds of miles between crests that may be just a few feet high. A passenger on a passing ship would scarcely detect their passing. But in fact the tsunami crest is just the very tip of a vast mass of water in motion. Though wind-driven waves and swells are confined to a shallow layer near the ocean surface, a tsunami extends thousands of feet deep into the ocean.
Because the momentum of the waves is so great, a tsunami can travel great distances with little loss of energy. The 1960 earthquake off the coast of Chile generated a tsunami that had enough force to kill 150 people in Japan after a journey of 22 hours and 10,000 miles. The waves from a trans-Pacific tsunami can reverberate back and forth across the ocean for days, making it jiggle like a planetary-scale pan of Jell-O.
02 May 2008
Think of a column of fluid of height h and cross sectional area A. The fluid has a density rho. The pressure P at the base of the column is by definition the force exerted on the base divided by the area A; that force is the weight of the column plus any force acting on the top. 
This is the formula for the pressure due to a column of fluid, or "hydrostatic pressure".
TSUNAMI & WAVES
A tsunami is not a sub-surface event in the deep ocean; it simply 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.
A tsunami wave in deep water creates a small but measurable change in pressure that will be maintained for as long as twenty minutes.
Tsunamis have tremendous force because of the great volume of water affected and the speed at which they travel. Just a cubic yard of water, for example, weighs about one ton. Although the tsunami slows to a speed of about 48 km/h (30 mph) as it approaches a coastline, it has a destructive force equal to millions of tons.
Waves are formed as the displaced water mass moves under the influence of gravity to regain its equilibrium and radiates across the ocean like ripples on a pond.
Tsunamis act very differently from typical surf swells; they are phenomena which move the entire depth of the ocean (often several kilometres deep) rather than just the surface, so they contain immense energy, propagate at high speeds and can travel great trans-oceanic distances with little overall energy loss.
The wave travels across open ocean at an average speed of 500 mph.
The passing "hump" mentioned earlier is a "momentum flux" equal to density multiplied by the square of the velocity. This gives the transient pressure built up during the quake as equal to twice and in addition to the hydrostatic pressure. There is no proof for this.
EXTRAS:
Pressure Waves and Shockwaves
As any object moves through the atmosphere is creates pressure waves. These are simply small disturbances caused by forcing air molecules closer together. These disturbances are then transmitted through the atmosphere, just like waves passing energy through the ocean.
A GOOD WEBSITE ON WAVE PRESSURE: http://www.pwri.go.jp/eng/ujnr/joint/37/paper/13kato.pdf
Sources used:
http://www.cbu.edu/~rprice/lectures/pressure.html
http://www.crystalinks.com/tsunami.html
http://selair.selkirk.bc.ca/aerodynamics1/High-Speed/Page2.html
28 APRIL 2008
For an example of how the environment effects a tsunami, the environment has to be in precise conditions for a tsunami to occur. A tsunami does not just happen out of the middle of the ocean, something has to cause it. On the simplest level tsunamis can be caused by an earthquake, but getting more in depth, the earthquake has a cause, that cause would be movement in tectonic plates, but what causes the movement in the tectonic plates? Is there a never ending cycle of events causing larger events causing larger events until one of them finally catches the human kinds notice and we take the incentive to do something about it. The moving of Tectonic plates is caused by something moving in one of the deeper layers of the earth. Something below the crust. The reason small movements are able to create earthquakes is that because the top 40 killometers of the earths crust are made up of tectonic plates, which rest upon magma which is constantly moving and so moving the plates. So, when a tectonic plate does get moved, it creates an earthquake, which creates an tsunami.  | ||||||||||||||
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| Damage from the tsunami can be very significant. But this damage does NOT seem all that significant to the environment .But behind the scenes lurks hidden damage. All of the damage from the tsunami, such as all the destroyed buildings, with fluids draining from these and leaking back into the ocean, into other farm land, or into rural areas. All of the fluids leaking from the buildings can harshly damage the environment by flooding into the oceans, where it may be drunk by sea creatures, or flowing into the farm land or just fields where it may ruin perfectly good soil. Not only does this damage the fish and ocean environment but it damages the human environment by ruining the economy. After the East India Tsunami the sea exports coming from East India took a hit of 30%. This was mainly because consumers were afraid the fish would be contaminated by the thousands of dead bodies which were washed out to sea.
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21 APRIL 2008
18 APRIL 2008
The described effects of tsunamis, as far as we have found, haven't taken into account how sea life is affected other than as a side note. With this tsunami, the effect on sea life and the associated ecosystems could well be massive.
When researching this entry, one of the most disturbing things we found was that there was very little available information regarding how sea life is affected. Without prior information, it's difficult to ascertain just how much of an impact that the tsunami will have on fishing, and subsequently, the region's economy. This is definitely an area where tsunami experts may wish to study - it's unlikely that this will be the last tsunami that humanity will encounter. The potential impact on humanity - through food and economy - gives such a study merit. As mentioned in an email in 1998 regarding underwater 'storms':
...Earthquakes can raise tsunami that act impact as huge unexpected waves when they arrive in shallow water. Unless the earthquake is near enough for animals to have sensed the vibrations and hidden, they will caught in the open by this large wave. In the 1750 Lisbon earthquake, reports record that the sea withdrew like a giant low tide, leaving fish flopping around on the seabed. People who went out to view this phenomenon, or to collect the fish, were drowned when the tsunami crashed back over the beaches...
In this particular scenario, it's easy to hypothesize that fish caught on the inside of the tsunami, had they sensed it, would have headed away from it - which would have been, in this massive bay, toward land. In doing so, they may have unwittingly become caught up in the wave. As the tsunami approaches land, it gains height even as it slows down. This would affect sea life within 1 kilometer of land, and perhaps even more depending on the depth of the tsunami in the open sea.
Deeper in the ocean, in the region of the earthquake, many things could have happened. Deformation of the sea floor is almost assured with an earthquake of this strength - but how the sea floor became deformed is open to speculation. That's really the bottom line with this tsunami - it's almost a theme - "We Do Not Know."
Because we do not know, it is time for us to start trying to find out. Maybe somewhere, there's a group of people working on this. And again, with all efforts being pointed toward saving the lives of our brothers and sisters, maybe it isn't. Yet knowing how much of an effect has been had on the sea life may well prepare the countries in the region for long term actions; while aid in the form of assistance and money rolls in, the long term effects will determine the long term assistance needed.
by FIONA
14 APRIL 2008
While society has been aware of the effects of fishing and overfishing for quite some time, the numbers tend to be human-centric. We've tried to make made it illegal for humans to inadvertently decimate fish stock although Mother Nature can do it with impunity. This doesn't excuse deep sea scraping; instead it makes humanity's effect on sea life more important. What we call a calamity under cover of a tsunami is something which we actually do ourselves a natural catastrophe. It's not usually the humble coastal fisherman who does this, instead the larger fishing operations yet the price paid is one of hunger.
by JINNY
6 APRIL 2008
like whoa look at her melons!
by charlotte
30 MARCH 2008
16 MARCH 2008
12 MARCH 2008
