Tsunami are huge oceanic waves which are formed because of powerful impact of natural cataclysms on all thickness of water. On coast of the Pacific Ocean more than 80% of cases of emergence of a tsunami are observed.
1. Underground earthquakes are the main reason for emergence of a tsunami. More than 85% of cases of emergence of these huge waves fall to their share. At an earthquake at an ocean floor there is a vertical motion of soil. A part of a bottom rises, and another – falls. The surface of the ocean begins to fluctuate down, seeking to return to a starting position, as generates a series of long waves.
2. Not each underwater earthquake leads to formation of a tsunami. Only rather strong earthquake with the center located superficially under a bottom can carry out a motion of all layer of water. Besides, underwater pushes have to enter a resonance with fluctuations of waves.
3. About 7% of a tsunami are a consequence of landslides. Often the earthquake leads to a landslide, and already it generates a powerful wave. Because of an earthquake on Alaska in 1958 in the bay Lutuya there was a landslide. The huge mass of ice and rocks collapsed from height of 1100 m in water. There was a wave which reached height more than 520 m on the opposite coast of the bay.
4. About 5% of tsunami formation are the share of underwater volcanic eruptions. Large volcanic explosions cause the shock wave shaking water weight. Besides, water starts moving, seeking to fill emptiness from the cast-out material. Huge tsunami were generated by a volcanic eruption of Krakatau in 1883.
5. Human activity can become the reason of emergence of a tsunami also. In 1948 as a result of the underwater atomic explosion made by the USA there was a wave 28.6 m high.
6. Falling of a large meteorite to the ocean can also cause destructive waves.
7. Waves up to 21 m high can be formed because of wind of storm force. However they are not a tsunami as in this case there is no motion of all thickness of a water layer. Besides, storm waves are short and cannot cause considerable floodings ashore.