Planet Earth that we walk on is made up of plates. Plates of the earth constantly moving, and rub against each other and collide. Friction and collision of the plates can cause vibration and mass dislocation event on the seabed will alter the behavior of a sudden sea. Perabahan behavior of
water waves generated by a tsunami.
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Diagram showing how earthquakes
can generate a tsunami. (Picture from: |
The word tsunami is made up of words
tsu and
nami in Japanese.
Tsu means harbor, while
nami means wave. Thus, tsunami means harbor crashing ocean waves. While a look at the process of events, the tsunami is a series of water waves with
wavelengths and very long period as a result of the activity of moving large amounts of
water.
Tsunamis are often associated with
earthquakes in oceanic regions. However, not all underwater earthquakes can cause
tsunamis. Tsunamis occur due to a strong earthquake that shallow seismic center of the dislocation caused by plate vertically on the seabed. If a fault occurs on the
sea floor plate, the plate of rock collapsed (fall) that
sea water is to be sucked on it. Due to the influence of gravity, the water is trying to get back to balance so that there is an oscillating water movement (up and down) to achieve balance. Water movement was later called a tsunami.
The main factor that determines the initial size of a tsunami is the amount of vertical deformation of the ocean. The amount of deformation is controlled partly by the great earthquake, the depth of the earthquake and the characteristics of the fault or faults. Other features that affect the size of a tsunami that struck the coastal shoreline and barimetrik configuration, the deformation velocity of the ocean, the water depth near the earthquake source, and the efficiency at which energy is channeled from the earth's crust into the water column.
Tsunamis can be generated by some disturbance which moved a number of water masses from the position of the
water balance.
Landslide on the ocean floor, which often occurs during a large earthquake, causing a mass of rock fell into the slope below it. As a result, the water that was above become elevated and then create a tsunami. During the underwater landslides, the balance of the sea level changed by the movement of ocean floor sediments.
Gravitational forces then propagate the tsunami and provide the initial disturbance on the surface of the sea. In the same way, a great eruption of the volcano, the sea can create an impulsive force to move the water column and generate a tsunami. Water in the avalanche can interfere with water on it. Falling debris move water from its equilibrium position and generate a tsunami.
Tsunami are characterized as
shallow water waves. Shallow water waves are different from the waves of
wind-generated waves, the waves that we often see on the beach. Waves generated by wind typically has a period of 5 to 20 seconds and a wavelength of about 100 to 200 meters.
A tsunami can have a period in a span of ten minutes to two hours and a wavelength of more than 500 kilometers. This is due to the long wavelengths that tsunamis behave as waves have shallow water. A wave is characterized as a shallow water wave when the ratio of water depth and its wavelength is very small. The rate of a shallow water wave equal to the root of the result of multiplying two acceleration of gravity and depth of the water.
Rate at the time the wave loses its energy is inversely proportional to wavelength. During the tsunami has a very large wavelength, tsunamis will be little loss of energy is propagated. Therefore, in very deep waters, the tsunami will spread very fast pace and spread across the vast ocean with little energy loss. For example, when at a depth of 6,100 meters of the ocean, tsunami spreading approximately 890 kilometers per hour, equal to the rate of a jet plane. Tsunamis can move from one region to other regions of the
Pacific Ocean in less than a day.
When leaving waters in the seas and spread to more shallow waters near the coast, tsunami transformed. Because the rate of tsunami related to the depth of water, as water depth decreases, the tsunami reduced rate. While the tsunami
total energy change is constant. Thus, the rate decreased when the tsunami enters shallow water, and the wave height increases. Meanwhile, when in deep water or the sea, the
tsunami wave height is only about 0.25 to 0.50 meters. That is why the ships are at sea often do not feel the tsunami, because of the short wave. When the tsunami reaches shallower places such as beaches, bays, harbors, or estuaries, the height of the waves into extraordinary ride. These waves can appear as a rapidly rising tide or into a series of breaking waves. Sea water is trapped so that its volume multiplied and raised to the power of a huge tsunami that damages and destroys the surrounding area. In the extreme case, the height of the tsunami could reach 30 feet for tsunamis generated near the epicenter of the earthquake.
Reefs, bays, estuaries, underwater features, and the slope of the beach all help to modify the tsunami as it approaches the coastal waves. When the tsunami enters the V-shaped bay, the greater the strength of the tsunami as it has a funnel effect. *** [GUN GUN GUNAWAN | PIKIRAN RAKYAT 26042012]
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