Tsunamis (Japanese for "big wave in the harbor") are sea gravity waves that result from upward or downward displacement of extended sections of the seabed during underwater and coastal earthquakes. Propagation speed from 50 to 1000 km / h. The height in the area of origin is from 0.1 to 5 m, near the coast - from 10 to 50 m and higher.
Tsunamis wreak havoc on land. For centuries, this unbridled natural phenomenon has kept people in awe, and therefore there is a lot of understatement about these killer waves.
Tsunami is a huge wave. Firstly, it is not one wave, but a whole series of waves coming to the shore one after another. Their number ranges from 3 to 25.
Second, not every wave is a tsunami. Storm, ship and other waves are the movement of only the upper layer of water, while a tsunami is the movement of its entire thickness.
Tsunami occurs from an underwater earthquake. A seaquake is the culprit in most tsunamis, but not always. Also typhoons, tropical cyclones, underwater landslides or volcanic eruptions can be the reasons. The largest waves are formed when a cosmic body - a comet or a meteorite - hits the ocean. The consequences of such a catastrophe can only be imagined and are unlikely to be survived. At one time, even dinosaurs died from this.
Any seaquake threatens a tsunami. For a tsunami to occur, the displacement of the bottom surface must be lightning fast and large enough to set the water column in motion. In addition, the source of the earthquake should not be too deep (up to 20 km.). Therefore, not every change in the topography of the ocean floor generates a giant wave.
Tsunamis occur only in warm seas. This myth arose because most of all tsunamis occurs in the Pacific Ocean, where seaquakes and underwater volcanic eruptions occur, and most often Japan and the Pacific Islands suffer from their impact. If we talk about landslide tsunamis arising from the collapse of rocks of sea cliffs, then they can happen everywhere! In 1964, due to an earthquake and subsequent ice collapse, a tsunami occurred in Alaska. It amazed with the height of its waves: 60 meters!
Before the tsunami begins, the water recedes from the coast. Canadian mathematician Walter Craig came to the conclusion that only half of the time the water really moves away from the coast, foreshadowing a tsunami. This depends primarily on the wavelength, and not on the power of the tsunami, as previously thought.
Tsunami is always a tall wave! Revealing the secret of this natural phenomenon, it must be said that in fact the height of a tsunami depends on its energy. And the farther from the epicenter, the higher the wave level. While in the open sea the tsunami does not exceed a meter, but moves at a breakneck speed, on the shallows the wave speed decreases and gains height. By the way, there may be no waves at all, and the tsunami will pass like a series of rapid ebb and flow. So the tsunami is not just a wall of water crashing onto the shore, but the movement of the entire water layer, increasing its destructive force when it meets land.
Tsunami comes unnoticed, which is why it is so difficult to escape from it. Indeed, a distinctive feature of a tsunami is its sudden appearance. But all the same, it makes itself felt, and if you are careful, you can notice the approach of a catastrophe. If an earthquake is the cause of a giant wave, everyone on the shore feels tremors, even if not strong. With a strong movement of water, small marine organisms glow. If a tsunami occurs in cold seas, ice breaks, underwater currents arise. In addition, water can leave the coast, draining the bottom, or, conversely, slowly tide.
The first tsunami wave is always the largest. This is not true. Since tsunami waves move one after another, and the distance between them can reach several tens or even hundreds of kilometers, they reach the coast after a certain time (from a couple of minutes to a whole hour). After the first wave, the shore gets wet, thereby reducing the resistance for subsequent waves. They are always more destructive.
Animals always feel the approach of a tsunami. Indeed, during the huge tsunami off the coast of Sri Lanka in 2004, not a single animal was found. Eyewitnesses claim that even the fish tried to hide from the oncoming elements, hiding in corals. But the truth is, not all animals are predictors of disaster. For some, the threat will become obvious, while the other will not react to it in any way. Therefore, it would be wrong to rely on the intuition of our smaller brothers in everything.
The only thing that saves you from the tsunami is a quick flight inland. Indeed, this is so, but it is important not only to run away from the coastline, but also to fulfill the simplest requirements: firstly, do not move along the river beds, where the tsunami wave will quickly overtake you. Secondly, going into the mountains, move up the slope, rising to a height of at least 30 meters from the coastline. Thirdly, if you are on a ship, boat or any other vessel, it is pointless to seek rescue on the shore, and it is better to go further into the sea. Finally, remember that the tsunami is returning. Only after a certain time you can return to the shore.