What is a tsunami? When does a tsunami occur?

Tsunami is one of the most devastating disasters of mankind.

What is a tsunami?

Tsunami (tsunami) is a series of waves created when a large volume of ocean water is flashed on a large scale. Earthquakes and large geological movements above or below the water surface, volcanic eruptions and meteorite impacts are all capable of causing tsunamis. The disastrous consequences of tsunamis can be enormous, killing by drowning in the water to hundreds of thousands of people in a few hours.

Tsunami.

The term tsunami (tsunami) originating from Japanese means "berth" (su tsu, Sino-Vietnamese pronunciation: "tan") and "wave" (波 nami, "three"). The term was set by fishermen, although at that time they did not know why the wave originated far away. The tsunami starts from the deep sea floor, while offshore, the wave has a small amplitude (wave height) but the length of the wave reaches hundreds of kilometers. So when it is far from the shore, it is difficult to recognize it, but only to feel a long wave of alcohol.

Causes of tsunami formation

Tsunami battles can form when the sea floor , suddenly deformed vertically, displaces the amount of water above it. Such large vertical movements of the Earth's crust can occur at the edge of the continental plate. Earthquakes are caused by special collisions or create tsunamis. When an ocean plate collides with a continental plate, it sometimes moves the edge of the continental plate downwards. Finally, the excessive pressure applied to the edge of the array made it snaps back to create waves that hit the Earth's crust, causing the earthquake to occur, known as the earthquake. Bottom of the sea.

The seabed landslides (sometimes due to earthquake causes) as well as volcanic collapses can also shock the water column, causing sediments and rocks to slide down the mountain slopes to the seabed. Similarly, a strong volcanic eruption under the sea can also bounce off a column of water to form a tsunami. The waves are formed when the displacement of water moves under the influence of gravity to regain balance and spread out across the ocean like ripples on the pond surface.

Tsunami formation.

In the 1950s it was discovered that large tsunamis can occur from landslides, volcanic eruptions and meteorite collisions. These phenomena caused a large amount of water to quickly be displaced, when the energy from an asteroid or an explosion moved into the water where the collision occurred. Tsunamis that appear from these causes, unlike tsunamis caused by earthquakes, often quickly disintegrate and rarely spread to the coast too far because of the small event area. These phenomena can cause large seismic waves in only one area. However, an extremely large landslide can cause a massive tsunami to affect the entire ocean.

The characteristics of tsunamis

The tsunami is very different depending on the wave type: they contain tremendous energy, propagate at high speed and can exceed large distances across the ocean with only very little energy loss. A tsunami can cause damage on the coast thousands of kilometers away where it arises, so we can have many hours of preparation since it's formed until it hits a beach, it appeared a long time after seismic waves formed from where the incident occurred. The energy per meter is long in the wave proportional to the inverse of the distance from the source.

Even a separate tsunami can involve a series of waves of different heights. In large waters, tsunamis have a very long cycle (the time for the next wave to reach a point after the previous wave), from several minutes to several hours, and the length of the wave is hundreds of kilometers. This is very different from the waves formed from normal wind on the ocean surface, they usually have a period of about 10 seconds and a wave length of 150 meters.

Tsunami in Japan in 2011.

The actual height of a tsunami in the ocean is usually less than a meter. This makes it difficult for people on board the ocean to recognize them. Because they have a large wave length, the energy of a tsunami controls the entire column of water, pointing it towards the sea floor. Ocean waves in deep water often occur due to water movement from the surface to a depth of half the wave length. This means that the movement of ocean surface waves only reaches a depth of about 100 m or less. In contrast, tsunamis act as waves of shallow waters in the open sea (because their length is at least 20 times greater than the depth where they operate), because the scattering of water moves less frequently. where deep water.

The wave passes through the ocean at an average speed of 500 miles per hour. As the land approached, the sea floor became shallow and the wave could no longer move quickly, so it began to "stand up"; The front part of the wave starts to stand and rise, and the distance between the short waves. Although a person outside the ocean may not notice the tsunami, when entering the shore it can reach a height of a six-story building or more. This upright process is the same as when you are waving a leather whip. When the waves advance from the end to the whip head, the same amount of energy is distributed in the smaller amount of material, making the movement become more intense. The more you enter the land, the slower the speed of travel but the wave is high.

A wave becomes a "shallow water wave" when the ratio between the water depth and its wave length is very small, and because the tsunami has a very long wave length (hundreds of kilometers), tsunamis acts as shallow water waves just outside the ocean. Shallow water waves move at a rate equal to the square root of the product between the gravitational acceleration (9.8m / s2) and the water depth. For example, in the Pacific Ocean, with an average depth of 4000m, a tsunami moves at about 200m / s (720km / h or 450 miles / hour) and loses little energy, even for intervals big way. At a depth of 40m, the speed will be 20m / s (about 72km / h or 45 miles / hour), smaller than the speed on the ocean but obviously people cannot run faster than this speed.

Hawai'i people flee before a tsunami is hitting Hilo, Hawai'i.

Signs of an upcoming tsunami

The following signs often foretell a tsunami:

1. Feel the earthquake. If you feel that the ground is shaking so hard that it can't stand, it's likely that a tsunami will happen.
2. Gas bubbles that float on the water make us feel like the water is boiling.
3. The water in the waves is unusually hot.
4. Water smells of rotten eggs (hydrogen sulfide gas) or gasoline and oil odors.
5. Water causes itchy skin.
6. Hearing an explosion sounded like: a jet engine's noise, the noise of a helicopter rotor, or a whistling sound.
7. The sea came back remarkably.
8. Dark clouds filled the sky.
9. Red light streaks on the horizon.
10. When the tsunami hits the shore, there will be a roar like a train approaching.
11. Millions of seagulls fly against the sea.
12. Many countries when there are tsunamis, often have warning sirens howling.

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