Tsunamis are long waves generated by powerful impact on all thickness of water in the ocean. More than 80% of tsunami occur on the periphery of the Pacific ocean. The reason most tsunamis are underwater earthquakes during which there is a sudden displacement of the sea floor.
The Pacific ocean is the "parent" of most of the tsunamis that we see on the planet. Reasons that cause tsunamis, the following:
Underwater earthquakes. During the earthquake part of the bottom sharply drops and the other rises dramatically. This pushes a large volume of water vertically upward, and the water, tending to take a horizontal position, creates a few waves.The eruption of volcanoes. A major eruption leading to the bottom of the movement, like an earthquake. The danger of a tsunami caused by the eruption that proseda down, the volcano creates a vast bowl-shaped depression. In an effort to fill it, the water creates a very long wave. Bad name have a tsunami created after the eruption of the volcano Krakatau. Seen in harbours around the world these tsunami over half a century, has destroyed 5000 ships, and killed 36 000 people.The landslides. Tsunamis can occur due to landslides infrequently. The last known case occurred in 1958, when Alaska ice mass and the land fell into the water with almost a kilometer of height by lifting the wave up to 50 m Local tsunami up to 20 m occur in Indonesia, where a large concentration of offshore savings.
Unlike ordinary waves, which arise, for example, during a storm, a tsunami affects the whole water column, not just the surface. Therefore, even small height of the tsunami can carry catastrophic character.
If the shore is shallow, the tsunami can be rolled without waves, and it looks like a series of sharp tides.
Funds that would have accurately identified the approaching wave does not exist. Therefore, if a storm swooped down gradually and people have time to retreat to a safe distance, the tsunami always rapid. Tsunamis are accompanied by a severe withdrawal of water from the shore, but to leave the place it's already too late.
For the vessel in the open sea, where the depth reaches several kilometers, the tsunami poses no danger, since wave height is only 1 m. the speed of the wave in the hearth reach 700 km/h. When approaching the shore with decreasing depth of the thickness of a moving wave rises to a height of 50 m, and decreases movement speed.
Tsunamis have multiple waves, the first and, as a rule, not the biggest, and misleading that the tsunami has passed. But the first wave only wets the shore, reducing the resistance to subsequent waves. A fatal mistake the dead is returning to shore after the initial destruction, where they are overtaken by the next biggest wave. Repeated waves may come at intervals of 2-3 hours.