## HOW ARE TSUNAMIS FORMED VIDEO

### Physical Characteristics of Tsunamis

Physical Characteristics of Tsunamis

All types of waves, including tsunamis, have a wavelength, a wave height, an amplitude, a frequency or period, and a velocity.

Wavelength is defined as the distance between two identical points on a wave (i.e. between wave crests or wave troughs). Normal ocean waves have wavelengths of about 100 meters. Tsunamis have much longer wavelengths, usually measured in kilometers and up to 200 kilometers

* Wave height refers to the distance between the trough of the wave and the crest or peak of the wave.
* Wave amplitude- refers to the height of the wave above the still water line, usually this is equal to 1/2 the wave height. Tsunamis can have variable wave height and amplitude that depends on water depth as we shall see in a moment
* Wave frequency or period - is the amount of time it takes for one full wavelength to pass a stationary point.
* Wave velocity is the speed of the wave. Velocities of normal ocean waves are about 90 km/hr while tsunamis have velocities up to 950 km/hr (about as fast as jet airplanes), and thus move much more rapidly across ocean basins. The velocity of any wave is equal to the wavelength divided by the wave period.

V = l/P

Tsunamis are characterized as shallow-water waves. These are different from the waves most of us have observed on a the beach, which are caused by the wind blowing across the ocean's surface. Wind-generated waves usually have period (time between two successive waves) of five to twenty seconds and a wavelength of 100 to 200 meters. A tsunami can have a period in the range of ten minutes to two hours and wavelengths greater than 500 km. A wave is characterized as a shallow-water wave when the ratio of the water depth and wavelength is very small. The velocity of a shallow-water wave is also equal to the square root of the product of the
acceleration of gravity, g, (980cm/sec/sec) and the depth of the water, d.

V=Ög * d

The rate at which a wave loses its energy is inversely related to its wavelength. Since a tsunami has a very large wavelength, it will lose little energy as it propagates. Thus, in very deep water, a tsunami will travel at high speeds with little loss of energy. For example, when the ocean is 6100 m deep, a tsunami will travel about 890 km/hr, and thus can travel across the Pacific Ocean in less than one day.

As a tsunami leaves the deep water of the open sea and arrives at the shallow waters near the coast, it undergoes a transformation. Since the velocity of the tsunami is also related to the water depth, as the depth of the water decreases, the velocity of the tsunami decreases. The change of total energy of the tsunami, however, remains constant

Furthermore, the period of the wave remains the same, and thus more water is forced between the wave crests causing the height of the wave to increase.
Because of this "shoaling" effect, a tsunami that was imperceptible in deep water may grow to have wave heights of several meters or more.
If the trough of the tsunami wave reaches the coast first, this causes a phenomenon called drawdown, where it appears that sea level has dropped considerably.
Drawdown is followed immediately by the crest of the wave which can catch people observing the drawdown off guard. When the crest of the wave hits, sea level rises (called run-up ).
Run-up is usually expressed in meters above normal high tide.

Run-ups from the same tsunami can be variable because of the influence of the shapes of coastlines. One coastal area may see no damaging wave activity while in another area
destructive waves can be large and violent. The flooding of an area can extend inland by 300 m or more, covering large areas of land with water and debris. Flooding tsunami waves tend to carry loose objects and people out to sea when they retreat.

Tsunamis may reach a maximum vertical height onshore above sea level, called a run-up height, of 30 meters. A notable exception is the landslide generated tsunami in Lituya Bay, Alaska in 1958 which produced a 60 meter high wave because the wavelengths and velocities of tsunamis are so large, the period of such waves is also large, and larger than normal ocean waves. Thus it may take several hours for successive crests to reach the shore. (For a tsunami with a wavelength of 200 km traveling at 750 km/hr, the wave period is about 16 minutes). Thus people are not safe after the passage of the first large wave, but must wait several hours for all waves to pass. The first wave may not be the largest in the series of waves. For example, in several different recent tsunamis the first, third, and fifth waves were the largest.
How Tsunamis Are Formed.
how-tsunamis-are-formed.

1. 我只知道，假如我去愛人生，那人生一定也會回愛我........................................

2. hello~welcome my world~<. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3. 寂寞又無聊 看到你的BLOG 加油喔!!........................................

4. 在莫非定律中有項笨蛋定律：「一個組織中的笨蛋，恆大於等於三分之二。」..................................................

5. 如果成為一支火柴，也要點亮一個短暫的宇宙；如果是一隻烏鴉，也要叫疼閉塞的耳膜。.............................................

6. 過去的事早已消失，未來的更是渺不可知，只有現在是真實的..................................................

7. 能猜得出女人真實年齡的男人也許耳聰目明，但肯定毫無大腦。哈哈！..................................................................

8. 我真心在追求我的夢想時，每一天都是繽紛的。因為我知道每一個小時都是實現理想 的一部份。..................................................

9. 認識自己,是發現妳的真性格、掌握妳的命運、創照你前程的根源。............................................................

10. 愛，拆開來是心和受兩個字。用心去接受對方的一切，用心去愛對方的所有。......................................................................

11. 愛，拆開來是心和受兩個字。用心去接受對方的一切，用心去愛對方的所有。......................................................................

12. 人生有如洶湧的波濤,如果沒有岩石的阻擋，怎能激起美麗的浪花？.......................................................

13. 當一個人內心能容納兩樣相互衝突的東西，這個人便開始變得有價值了。............................................................

14. 卡爾.桑得柏：「除非先有夢，否則一切皆不成。」共勉！.. .. ............................................................