Such a phenomenon as a tsunami is as old and indomitable as the ocean. Eyewitness accounts of the terrible waves passed from mouth to mouth over time became legends, and about 2,000-2,500 years ago, written evidence began to appear. Among the probable reasons for the disappearance of Atlantis, which happened about 10,000 years ago, some of the researchers also call giant waves.
The word "tsunami" came to us from the Land of the Rising Sun. It is Japan that is most affected by the tsunami on the planet. She felt the dire consequences of the tsunami, which took many thousands of lives and caused enormous material damage. Tsunamis occur most often in the Pacific Ocean. In Russia, the Far Eastern shores - Kamchatka, the Kuril and Commander Islands and, partially, Sakhalin - are subject to regular attacks by giant waves.
What is a tsunami? A tsunami is a giant wave that captures a huge amount of water and raises it to great heights. Such waves are found in oceans and seas.
The occurrence of a tsunami
What can make ordinary water transform into such a destructive phenomenon of nature, endowed with a truly hellish power?
Tsunamis are long and high waves generated as a result of a powerful impact on the entire water column in the ocean or other body of water.
A common cause of catastrophic tsunamis is activity that occurs in the interior of the Earth. For the most part, water monsters provoke underwater earthquakes, so the study of this destructive phenomenon became possible only after the science of seismology appeared. A direct dependence of the wave strength on the strength of the earthquake was recorded. This is also influenced by the depth at which the shock occurred. Thus, only waves generated by high-energy earthquakes with a magnitude equal to or greater than 8.0 have significant destructive power.
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Observations show that tsunamis occur when an area of the sea or ocean surface is unexpectedly displaced in the vertical direction after the corresponding area of the seabed is also displaced. Experts understand by tsunamis the so-called long-period (that is, far from each other) sea gravitational waves that suddenly appear in the seas and oceans precisely as a result of earthquakes, the sources of which are under the bottom.
The ocean floor shudders with colossal energy and produces huge faults and cracks that lead to subsidence or elevation of significant areas of the bottom. As if a giant underwater ridge directs the entire volume of water from the bottom to the surface itself, in all directions from the hearth. Oceanic water at the very surface may not absorb this energy at all, and vessels passing through them may simply not notice the serious disturbance of the waves. And in the depths, the future disaster begins to gain momentum and rushes at breakneck speed to the nearest shores.
Tsunamis also arise from explosions of underwater volcanoes, and as a result of bottom landslides. Coastal landslides caused by the fall of a huge mass of rock into the water can also cause a tsunami. Tsunamis with foci at great depths usually have a great destructive force. In addition, the causes of tsunamis are surges in bays caused by typhoons, storms and strong tides, which, as you can see, can explain the origin of the Japanese word "tsunami", which translates as "big wave in the harbor."
Giant waves have great speed and enormous energy, and therefore are capable of being thrown far out onto land. When approaching the coast, they deform and, rolling onto the coast, produce enormous destruction. In the open ocean, water monsters are not high, not exceeding heights of 2-3 m during the strongest earthquakes, but at the same time they have a considerable length, sometimes reaching 200-300 km, and an incredible propagation speed.
Approaching the coast, depending on the coastal bottom topography and the shape of the coastline, giant waves can grow up to several tens of meters. Getting into a shallow coastal zone, the wave changes - its height increases and, at the same time, the steepness of the leading front increases. When approaching the shore, it begins to overturn, creating a foaming, bubbling, high-altitude water stream crashing onto the shore. In such cases, river mouths are quite dangerous, along which monstrous waves are able to penetrate into the depths of the territory for a distance of several kilometers.
Tsunami - aftermath
1946, April 6 - the city of Hilo on the island of Hawaii experienced the full power of the disturbance of the water element. Residential buildings and administrative buildings were overturned, asphalted roads and beaches disappeared, the railway bridge was moved 300 meters upstream, and boulders weighing several tons were scattered throughout the devastated area. This was the result of a displacement of the ocean floor that occurred at a distance of 4,000 km from Hilo, in the Aleutian Islands.
The shock gave rise to a series of tsunamis that swept across the Pacific Ocean at a speed of more than 1,100 km / h, reaching a height of 7.5 to 15 m. The water element with all its fury pounced on land and literally tore everything that it managed to embrace with its foamy embrace. Waves of this kind travel in all directions from the point where they appeared, at large intervals, but at an alarming speed. While the distance between normal sea waves is about 100 m, tsunami wave crests follow each other at intervals from 180 km to 1200 km. Therefore, the passage of each such wave is accompanied by a deceptive lull.
That is why, when the first wave in Hilo subsided, many residents descended to the shore to understand the scale of the destruction, and were washed away by the next giant wave. The eyewitness account said:
“The tsunami waves, steep and eddy, rushed to the shore. Between the ridges, the water receded from the coast, exposing reefs, coastal silt accumulations and the bottom of the bay at a distance of 150 meters or more beyond the usual coastline. The water rolled back swiftly and violently, with a hiss, hiss and a crash. In several places, houses were washed into the sea, in some places even huge rocks and concrete blocks were carried over the reefs. The people, along with their belongings, were carried out to sea, and only a few of them were rescued several hours later with the help of boats and life rafts dropped from aircraft."
If the speed of a simple wind wave is capable of reaching 100 km / h, then tsunami waves move at the speed of a jet plane - from 900 to 1500 km / h. The lethal effect of the elements is determined not only by the power of the shock that generated the tsunami, but also by the terrain along which the giant wave is traveling, and the distance from the coast.
Of course, they are more dangerous on gentle coasts than on steep ones. When the bottom has cliffs, the oncoming waves will not rise to a sufficient height, but, hitting a gentle shore, they often reach the height of a six-story building or more. When these waves enter the bay or inlet in the form of a funnel, each of them brings a violent flood onto the shore. The height of the wave decreases only in closed expanding bays with a narrow entrance, and when it hits the river, the wave increases in size, increasing its destructive power.
The activity of a volcano in the water column gives an effect that can be compared with a strong earthquake. The greatest giant wave ever known was caused by the powerful eruption of the Krakatoa volcano in Indonesia in 1883, when a huge mass of rock was thrown into the air to a height of several kilometers and turned into a dust cloud that circled our planet three times.
Sea waves rushing one after another, up to 35 m high, drowned over 36,000 inhabitants of the nearby islands. They circled the entire globe and were spotted in the English Channel a day later. A military vessel, located off the coast of Sumatra, threw 3.5 km inland, where it got stuck in a thicket 9 m above sea level.
Another stunning case of an unusually high wave was recorded on July 9, 1958. After the earthquake in Alaska, a mass of ice and earth rocks with a volume of about 300 million cubic meters. m collapsed into the narrow and long bay of Lituya, causing a colossal wave splash on the opposite side of the bay, reaching almost 60 meters in height on certain parts of the coast. At that time, there were three small fishing boats in the bay.
“Despite the fact that the disaster took place 9 km from the ship's anchorage,” says an eyewitness, “everything looked terrible. Before the eyes of the shocked people, a huge wave rose up, engulfing the foot of the northern mountain. Then she swept across the bay, stripping trees from the slopes of the mountains, destroying the recently abandoned camp site of climbers; falling like a water mountain on the island of Cenotaphia, it swallowed up the old hut and, in the end, rolled over the highest point of the island, which rose 50 m above sea level.
The wave spun Ulrich's ship, which, losing control, rushed at the speed of a galloping horse towards the Swanson and Wagner ships, still at anchor. To the horror of the people, the wave broke the anchor chains and dragged both ships like chips, forcing them to overcome the most incredible path that once fell to the lot of fishing vessels. Below the ship, Swanson said, they saw the tops of 12-meter trees and rocks the size of a house. The wave literally threw people across the island into the open sea."
Over the centuries, tsunamis have become the culprits of terrible world catastrophes.
1737 - a case of a giant wave on the Kamchatka coast is described, when the waves washed away almost everything that was in the flood zone. The small number of casualties was due only to the small number of residents.
1755 - due to the fault of a water monster, the city of Lisbon was completely wiped off the ground, the death toll was more than 40,000 people.
1883 - Tsunami caused colossal damage to the shores of the Indian Ocean, the death toll is more than 30,000.
1896 - the water element hit the shores of Japan, the death toll is more than 25,000.
1933 - The coast of Japan was damaged again, more than a thousand buildings were destroyed, 3,000 people died.
1946 - the most powerful tsunami caused huge damage to the islands and the coast near the Aleutian Gap; total loss of more than $ 20 million.
1952 - the enraged ocean pounced on the northern coast of Russia, and although the waves were no more than 10 meters high, the damage was enormous.
1960 - the coast of Chile and surrounding territories suffered from the raid of giant waves, the damage was more than $ 200 million.
1964 - The Pacific coast is attacked by a tsunami that destroyed over $ 100,000 worth of buildings, roads and bridges.
In recent years, it has been established that giant waves can cause even "space guests" - meteorites that did not have time to burn up in the earth's atmosphere. Perhaps a few tens of millions of years ago, the fall of a giant meteorite led to a tsunami, which led to the death of the dinosaurs. Another, quite banal reason, may be the wind. He is able to cause a large wave only under the right circumstances - the air pressure must be correct.
However, the most important thing is that a person is capable of provoking a "man-made" tsunami himself. This is exactly what the Americans proved in the middle of the 20th century, having experienced an underwater nuclear explosion, which caused huge underwater disturbances and, as a result, the appearance of monstrous high-speed waves. Be that as it may, even now man cannot predict for sure the appearance of a tsunami and, what is even more terrible, stop it.
E. Gurnakova