Tsunamis are also often confused with storm surges, even though they are quite different phenomena. For tsunamis that are generated by underwater earthquakes, the amplitude of the tsunami is determined by the amount by which the sea-floor is displaced. As well as travelling at high speeds, tsunamis can also travel large distances with limited energy losses. As a tsunami leaves the deep water of the open-ocean and travels into the shallower water near the coast, it transforms. Just like other water waves, tsunamis begin to lose energy as they rush onshore - part of the wave energy is reflected offshore, while the shoreward-propagating wave energy is dissipated through bottom friction and turbulence.
Tsunamis have great erosion potential, stripping beaches of sand that may have taken years to accumulate and undermining trees and other coastal vegetation. In the deep ocean, a tsunami has a small amplitude (less than 1 metre) but very long wavelength (hundreds of kilometres).
Tide gauges measure the height of the sea-surface and are primarily used for measuring tide levels.
The tide gauge at Cocos Island observed the tsunami on December 26th 2004 as it passed by the island, as shown in these observations made during December. In 1995 the National Oceanic and Atmospheric Administration (NOAA) began developing the Deep-ocean Assessment and Reporting of Tsunamis (DART) system. An undersea earthquake in the Indian Ocean on 26th December 2004 produced a tsunami that caused one of the biggest natural disasters in modern history. The waves devastated the shores of parts of Indonesia, Sri Lanka, India, Thailand and other countries with waves reported up to 15 m high, reaching as far as Somalia on the east coast of Africa, 4500 km west of the epicentre. Due to the distances involved, the tsunami took anywhere from fifteen minutes to seven hours (for Somalia) to reach the various coastlines. On its arrival on shore, the height of the tsunami varied greatly, depending on its distance and direction from the epicentre and other factors such as the local bathymetry. Tide: The term ‘tide’ refers to the alternate rising and falling of the sea level at shores. Earthquake: A sudden and violent movement of a portion of the earth’s crust, and the series of vibrations that follow. Teletsunami: A tsunami which causes damage a long distance away from the source has been given the name ‘teletsunami’.
Tsunami waves are caused by large underwater earthquakes where there are tectonic plate boundaries. When the pressure of the tectonic plate at the ocean floor releases pressure, it causes the water above to create a series of rolling waves which will build up to cause more turbulent and fast moving waves. Some people might left be trapped under buildings for long periods of time while search and rescue teams attempt to get a hold on the situation.
Tsunamis can cause economic decline as they have to spend a lot of money rebuilding the houses and restoring the original landscape. One of the most well known and recent incidence of a tsunami was in Indonesia, on the 26th of December 2004. Due to the distances involved, the disastrous tsunami took between fifteen minutes and seven hours to reach the all the different coastlines. The earthquake which caused the tsunami affected many countries even beyond Southeast Asia. A tsunami is a series of ocean waves that sends surges of water, sometimes reaching heights of over 100 feet (30.5 meters), onto land.
The day after Japan's biggest earthquake, cities smoldered, soldiers lent helping hands, and a nuclear reactor exploded. The biggest earthquake in Japan's history Friday sparked three-story waves, hundreds of casualties, and towering infernos. In light of Friday's tsunami following the Japan earthquake, find out how the killer waves are caused, what the warning signs are, and how to respond when a tsunami threatens. The deadly earthquake that struck Japan Friday sent a tsunami racing across the Pacific Ocean, reaching Hawaii, the Pacific Northwest, and California.
Southern California, Seattle, and Taiwan are some of the places where tsunamis may be more likely than thought, a new study says. See heroic firefighters and breathtaking devastation shared with the #wildfire2014 tag on Your Shot. Twisters across much of the South and Midwest highlight seasonal dangers in vast strike zone.
The National Geographic Society aims to be an international leader for global conservation and environmental sustainability. On March 11, 2011, a magnitude-9 earthquake shook northeastern Japan, unleashing a savage tsunami. The total damages from the earthquake and tsunami are estimated at $300 billion dollars (about 25 trillion yen), according to the Japanese government. Scientists drilled into the subduction zone soon after the earthquake and discovered a thin, slippery clay layer lining the fault. Less than an hour after the earthquake, the first of many tsunami waves hit Japan's coastline. The tsunami caused a cooling system failure at the Fukushima Daiichi Nuclear Power Plant, which resulted in a level-7 nuclear meltdown and release of radioactive materials.

The surge of water carried an estimated five million tons of debris out to sea, the National Oceanic and Atmospheric Agency has reported.
In Norway, water in fjords pointing toward Japan sloshed back and forth as seismic waves from the earthquake raced through. The earthquake produced a low-frequency rumble called infrasound, which traveled into space and was detected by the Goce satellite. Buildings destroyed by the tsunami released thousands of tons of ozone-destroying chemicals and greenhouse gases into the air.
Please listen to your local radio and TV announcements or call 1300 TSUNAMI (1300 878 6264) for latest warning information. Similarly, the wavelength and period of the tsunami are determined by the size and shape of the underwater disturbance.
As the tsunami propagates across the ocean, the wave crests can undergo refraction (bending), which is caused by segments of the wave moving at different speeds as the water depth along the wave crest varies. If you read the "The physics of a tsunami" section, you will know that a tsunami travels at a speed that is related to the water depth - hence, as the water depth decreases, the tsunami slows.
So a tsunami with a height of 1 m in the open ocean where the water depth is 4000m would have a waveheight of 4 to 5 m in water of depth 10 m. Capable of inundating, or flooding, hundreds of metres inland past the typical high-water level, the fast-moving water associated with the inundating tsunami can crush homes and other coastal structures.
These are sent down to the ocean surface from the satellite and the height of the ocean surface can be determined by knowing the speed of the pulse, the location of the satellite and measuring the time that the pulse takes to return to the satellite. The data were taken by a radar altimeter on board the satellite along a track traversing the Indian Ocean when the tsunami waves had just filled the entire Bay of Bengal.
Refraction and diffraction of the waves meant that the impact of the tsunami was noticed around the world and sea-level monitoring stations in places such as Brazil and Queensland also felt the effect of the tsunami. A numerical model was used to replicate the generation and propagation of the tsunami and it shows how the waves propagated around the world's ocean basins. With a magnitude of 9.0 on the Richter scale, it was the largest since the 1964 earthquake off Alaska and equal fourth largest since 1900, when accurate global seismographic record-keeping began. It was a rare megathrust earthquake and occurred on the interface of the India and Burma tectonic plates. Plates slide along either beside, over or under each other, causing friction and pressure between the plates. These types of tsunamis are not produced by horizontal motions, but by vertical motions in the seabed. This is due to the amount of earthquake and volcanic activity in the area, which occur due to the tectonic shifts in the earth’s plates. When it reaches the shore, it produces what is described as the ‘vacuum effect’, which sucks the coastal water into the sea and gives the opposite effect of a tsunami.
A 9.3 magnitude earthquake triggered a series of giant tsunamis along the coasts of most landmasses that bordered the Indian Ocean. These other countries included Sri Lanka, India, Malaysia, Thailand, Myanmar, the Maldives, Seychelles, Somalia, Tanzania and South Africa. This is an aerial view of damage to Sukuiso, Japan, a week after the earthquake and subsequent tsunami devastated the area in March, 2011. Radioactive water was recently discovered leaking from the Fukushima Daiichi Nuclear Power Plant, which suffered a level 7 nuclear meltdown after the tsunami. That record goes to the 2004 Banda Aceh earthquake and tsunami in Sumatra, a magnitude-9.1, which killed more than 230,000 people. The country's stringent seismic building codes and early warning system prevented many deaths from the earthquake, by stopping high-speed trains and factory assembly lines. The tsunami waves reached run-up heights (how far the wave surges inland above sea level) of up to 128 feet (39 meters) at Miyako city and traveled inland as far as 6 miles (10 km) in Sendai. The electrical power and backup generators were overwhelmed by the tsunami, and the plant lost its cooling capabilities.
Researchers sailed offshore and dropped sensors along the fault line to measure the forces that caused the earthquake. In Chile, some 11,000 miles (17,000 km) distant, the tsunami was 6.6 feet (2 meters) high when they reached the shore, according to the Pacific Tsunami Warning Center. The term "tidal wave" is misleading; even though a tsunami's impact upon a coastline is dependent upon the tidal level at the time a tsunami strikes, tsunamis are unrelated to the tides. The tsunami's energy flux, which is dependent on both its wave speed and wave height, remains nearly constant.
Depending on whether the first part of the tsunami to reach the shore is a crest or a trough, it may appear as a rapidly rising or falling tide. Tsunamis may reach a maximum vertical height onshore above sea level, often called a run-up height, of tens of metres. One problem with this kind of satellite data is that it can be very sparse - some satellites only pass over a particular location about once a month, so you would be lucky to spot a tsunami since they travel so quickly. The data shown are the differences in sea surface height from previous observations made along the same track 20-30 days before the earthquake, showing the signals of the tsunami. These stations give detailed information about tsunamis while they are still far off shore.
The northern regions of the Indonesian island of Sumatra were hit very quickly, while Sri Lanka and the east coast of India were hit roughly two hours later.

The closer they get to the shoreline and enter shallower water, their energy and height grow to drastic measures. When this occurs, the sea floor is left completely waterless and the seafloor is totally exposed. This gives people little time to escape the wrath of the tsunami; however the warning can save lives. Australia and Europe had a large number of their citizens in the region at the time of the disaster, along with many other countries.
Japan relies on nuclear power, and many of the country's nuclear reactors remain closed because of stricter seismic safety standards since the earthquake.
But Japan's one-two punch proved especially devastating for the earthquake-savvy country, because few scientists had predicted the country would experience such a large earthquake and tsunami. The great plates are rough and stick together, building up energy that is released as earthquakes.
People in Japan also received texted alerts of the earthquake and tsunami warnings on their cellphones.
The tsunami flooded an estimated area of approximately 217 square miles (561 square kilometers) in Japan.
In some regions, such as Miyagi and Fukushima, only 58 percent of people headed for higher ground immediately after the earthquake, according to a Japanese government study published in August 2011. Teams studied the tsunami deposits to better understand ancient sediment records of the deadly waves.
Becky was a science reporter at The Pasadena Star-News and has freelanced for New Scientist and the American Institute of Physics.
The acoustic sensor emits a sound pulse which travels from the top of the tube down to the water surface, and is then reflected back up the tube.
However, during the Indian Ocean tsunami of December 26th 2004, the Jason satellite altimeter happened to be in the right place at the right time. Each station consists of a sea-bed bottom pressure recorder which detects the passage of a tsunami.
Thailand was also struck about two hours later, despite being closer to the epicentre, because the tsunami travelled more slowly in the shallow Andaman Sea off its western coast. The speed and momentum increases due to the top of the waves moving faster that the bottom does. When a tsunami hits it is important for people to remember that the danger may not have passed with the first wave or two. The east coast of India and Sri Lanka were hit somewhere between 90 minutes to two and a half hours later.
Many people also underestimated their personal risk, or assumed the tsunami would be as small as ones they had previously experienced, the study found. Earthquake engineers examined the damage, looking for ways to build buildings more resistant to quakes and tsunamis.
This large vertical displacement of the sea-floor generated the devastating tsunami, which caused damage over such a large area around the Indian Ocean. Thailand was hit around two hours later despite the fact that it was closer to the epicentre The reason for this is because the water was more shallow in the Andaman Sea, which is off the western coast. In the decade before the 2011 Tohoku earthquake, a handful of Japanese geologists had begun to recognize that a large earthquake and tsunami had struck the northern Honshu region in 869.
Coast Guard fired on and sank the derelict boat 164-foot Ryou-Un Maru in 2012 in the Gulf of Alaska. Because of this shoaling effect, a tsunami that is unnoticeable at sea, may grow to be several metres or more in height near the coast. This system filters out small-scale effects like wind-waves and has the capacity to measure sea-level changes within 1mm accuracy. The best defense against any tsunami is early warning that allows people to seek higher ground.
And their long wavelengths mean they lose very little energy along the way.In deep ocean, tsunami waves may appear only a foot or so high. The surface buoy then radios the information to the Pacific Tsunami Warning Center (PTWC) via satellite. But as they approach shoreline and enter shallower water they slow down and begin to grow in energy and height. Now, tsunami experts from around the world have been asked to assess the history of past tsunamis in Japan, to better predict the country's future earthquake risk. The system has considerably improved the forecasting and warning of tsunamis in the Pacific.
When it does, it produces a vacuum effect that sucks coastal water seaward and exposes harbor and sea floors. Recognizing this phenomenon can save lives.A tsunami is usually composed of a series of waves, called a wave train, so its destructive force may be compounded as successive waves reach shore. The Pacific Tsunami Warning System, a coalition of 26 nations headquartered in Hawaii, maintains a web of seismic equipment and water level gauges to identify tsunamis at sea.

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