Saturday, August 15, 2009

What is Tsunami?

Tsunamis are giant waves, initiated by a sudden change (usually in relative position of underwater tectonic plates). The sudden change is typically enough to propagate the wave; however, its power can be enhanced and fed by lunar positioning and boundaries that focus its energy.
Tsunami is a great sea wave produced by a submarine earthquake, volcanic eruption, or large landslide.
Tsunami is a sea wave of local or distant origin that results from large-scale seafloor displacements associated with large earthquakes, major submarine slides, or exploding volcanic islands. (See also Earthquake ABC’s.)
Definiton of Tsunami :Tsunami is an ocean wave produced by a sub-marine earthquake, landslide, or volcanic eruption. These waves may reach enormous dimensions and have sufficient energy to travel across entire oceans.
Tsunami is an ocean wave generated by a submarine earthquake, volcano or landslide. (Also known as a seismic seawave, and incorrectly as a tidal wave).
Tsunamis are one or a series of huge sea waves caused by earthquakes or other large-scale disturbance of the ocean floor. (Referred to incorrectly by many as a tidal wave, but these waves have nothing to do with tides.) The word tsunami is Japanese, meaning “harbor wave.”
Tsunami is a sea wave produced by any large-scale disturbance of the sea floor, principally by a submarine earthquake or by submarine earth movement.
Tsunami is a rare, giant wave that is caused by an underwater earthquake or other large-scale, underwater disturbance. tuff Tuff is pyroclastic rock. tumbled Tumbled stones were finished in a tumbler, a mechanical device that smooths and rounds the surfaces of stones. Tumbled stones look very much like stones that have been in a fast-flowing river or stream for a long time. tumbler A tumbler is a rotating cylinder (powered by a motor) that smooths and rounds the surfaces of stones, increasing their luster. As the stones tumble around the cylinder, they bump against each other and
Tsunamis are vast sea waves caused by the sudden dropping or rising of a section of the sea floor following an earthquake. Tsunami may be as much as 30 meters high and 200 kilometers long, may move as fast as 250 kilometers per hour, and may continue to occur for as long as a few days.

What is the meaning of Tsunami?

Tsunami is a Japanese word with the English translation, "harbor wave." Represented by two characters, the top character, "tsu," means harbor, while the bottom character, "nami," means "wave." In the past, tsunamis were sometimes referred to as "tidal waves" by the general public, and as "seismic sea waves" by the scientific community. The term "tidal wave" is a misnomer; although 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. Tides result from the imbalanced, extraterrestrial, gravitational influences of the moon, sun, and planets. The term "seismic sea wave" is also misleading. "Seismic" implies an earthquake-related generation mechanism, but a tsunami can also be caused by a nonseismic event, such as a landslide or meteorite impact

The Effect Of Tsunami

- 1946 - tsunami killed 165 people in Hawaii/Alaska, resulted in creation of tsunami warning
- 1960 – Chile strongest quake ever recorded (magnitude 9.5) off coast of south central Chile,
one of the most destructive tsunamis of the 20th century. waves measured up to 25 metres
high. tsunami hit Onagawa, Japan 22 hrs after the quake with waves 3 m above the tide. killed
about (estimation) 2290 people.
- 1964 - good friday - magnitude 9.2 quake, tsunamis struck Alaska, d killed
122 peoplestsunamis were up to 6 m tall.
- 2004 - Indian ocean - magnitude 9.2 quake triggered a lethal series of tsunamis on December
26, killed over 310,000 people (over 220,000 in Indonesia alone), deadliest tsunami in
recorded history, killed people in Indonesia/Thailand all the way to India, Bangladesh (several
thousand km’s away) and even as far as eastern Africa (Kenya, Somalia, Tanzania). over
$600M was raised to help the victims. unlike the pacific ocean, there is no alert system
covering the Indian ocean. there had not been a tsunami there since the krakatoa volcanic
eruption tsunami in 1883. UNESCO and other world bodies have called for a global tsunami
monitoring system.

Causes Of Tsunami?

What causes a tsunami?... A tsunami is a large ocean wave that is caused by sudden motion on the ocean floor. This sudden motion could be an earthquake, a powerful volcanic eruption, or an underwater landslide. The impact of a large meteorite could also cause a tsunami. Tsunamis travel across the open ocean at great speeds and build into large deadly waves in the shallow water of a shoreline.

Subduction Zones are Potential Tsunami Locations

Most Tsunamis are caused by earthquakesgenerated in a subduction zone, an area where an oceanic plate is being forced down into the mantle by plate tectonic forces. The friction between the subducting plate and the overriding plate is enormous. This friction prevents a slow and steady rate of subduction and instead the two plates become "stuck".
Image by USGS

Accumulated Seismic Energy

As the stuck plate continues to descend into the mantle the motion causes a slow distortion of the overriding plage. The result is an accumulation of energy very similar to the energy stored in a compressed spring. Energy can accumulate in the overriding plate over a long period of time - decades or even centuries.
Image by USGS

Earthquake Causes Tsunami

Energy accumulates in the overriding plate until it exceeds the frictional forces between the two stuck plates. When this happens, the overriding plate snaps back into an unrestrained position. This sudden motion is the cause of the tsunami - because it gives an enormous shove to the overlying water. At the same time, inland areas of the overriding plate are suddenly lowered.
Image by USGS

Tsunami Races Away From the Epicenter

The moving wave begins travelling out from where the earthquake has occurred. Some of the water travels out and across the ocean basin, and, at the same time, water rushes landward to flood the recently lowered shoreline.
Image by USGS

Tsunamis Travel Rapidly Across Ocean Basis

Tsunamis travel swiftly across the open ocean. The map below shows how a tsunami produced by an earthquake along the coast of Chile in 1960 traveled across the Pacific Ocean, reaching Hawaii in about 15 hours and Japan in less than 24 hours.
Image by USGS
Tsunami "Wave Train"
Many people have the mistaken belief that tsunamis are single waves. They are not. Instead tsunamis are "wave trains" consisting of multiple waves. The chart below is a tidal gauge record from Onagawa, Japan beginning at the time of the 1960 Chile earthquake. Time is plotted along the horizontal axis and water level is plotted on the vertical axis. Note the normal rise and fall of the ocean surface, caused by tides, during the early part of this record. Then recorded are a few waves a little larger than normal followed by several much larger waves. In many tsunami events the shoreline is pounded by repeated large waves.
Image by USGS
The material above describes how tsunamis are generated and how they travel rapidly across an ocean basin. For more detailed information on this topic the following websites are recommended.

Tsunami in History

Tsunami are not rare, with at least 25 tsunami occurring in the last century. Of these, many were recorded in the Asia–Pacific region—particularly Japan. The 2004 Indian Ocean Tsunami caused approximately 350,000 deaths and many more injuries.
As early as 426 B.C. the Greek historian Thucydides inquired in his book History of the Peloponnesian War about the causes of tsunami, and argued correctly that it could only be explained as a consequence of ocean earthquakes.[2] He was thus the first in the history of natural science to correlate quakes and waves in terms of cause and effect:[3]
The cause, in my opinion, of this phenomenon must be sought in the earthquake. At the point where its shock has been the most violent the sea is driven back, and suddenly recoiling with redoubled force, causes the inundation. Without an earthquake I do not see how such an accident could happen.[15]
The Roman historian Ammianus Marcellinus (Res Gestae 26.10.15-19) described the typical sequence of a tsunami, including an incipient earthquake, the sudden retreat of the sea and a following gigantic wave, after the 365 A.D. tsunami devastated Alexandria.[16][17]

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