Tsunami: what it is, causes, types, consequences, photos and videos * Planet Earth

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The tsunami is one of the dangerous and destructive phenomena, which is still not fully investigated by experts. What is this phenomenon, why does it occur and what causes the consequences? We also consider the tsunami classification and the most famous cases in history.

What is a tsunami?

Translated from the Japanese word "tsunami"Indicates a wave in the bay. In other words, these are large waves that are formed as a result of the strongest impact on the water column in the ocean or sea.

The main difference between this natural phenomenon and ordinary high waves lies precisely in the nature of their origin. If ordinary waves are formed only on the surface of the water, then the tsunami covers its entire thickness. The size of the waves depends on the volume of the reservoir.

The average wave height is 10-40 meters. Tsunamis spread at speeds up to 900 km / h. They can take various forms. Often these are several waves that roll onto the shoreline with a certain period of time - from 3 minutes to 2 hours. Sometimes the elements are alternating ebbs and flows.

Interesting fact: The maximum wave height that was recorded during the tsunami is more than 500 meters.

Do not confuse the tsunami and typhoon, as these are two completely different natural phenomena. The common between them is only the speed of propagation. Typhoons occur only on the surface of the water and are caused by strong winds. Tsunamis are more powerful and are characterized by several damaging factors.

Causes

The causes of the tsunami can be divided into the most common and probable. In most cases, this phenomenon occurs under the influence of several factors simultaneously. A tsunami occurs if the activating factor has sufficient strength.

The most common factors:

underwater earthquake;
landslides;
eruption.

An earthquake in 85% of cases causes a tsunami. In this case, changes occur at the bottom of the reservoir, namely, displacement. As a result, part of the bottom goes down, and the other part goes up. This displacement causes vibrations of water in the vertical direction. She seeks to return to its original position - the middle level, so waves form.

A tsunami does not occur after every earthquake. Only tremors, the foci of which are shallow, can cause strong waves. The difficulty is that specialists still cannot determine the tsunamigenic earthquakes as accurately as possible.

Landslides cause tsunamis in 7% of casesalthough earlier this factor was greatly underestimated. They are formed in combination with earthquakes, or rather, landslides often arise due to strong shocks. At the same time, massive rocks collapse, often in conjunction with ice.

Volcanic eruptions occupy 5% of the total tsunami. They create the same effect as tremors. Moreover, during the eruption, water can fill the cavities that occur during the collapse of the walls of the crater. This phenomenon allows the tsunami wave to actively grow in length.

Other possible causes:

meteorite fall;
strong wind;
human activities.

If a sufficiently large meteorite falls into a body of water, it is able to create a wave. But it takes on a circular shape and rapidly loses power, without turning into a tsunami. A true element can arise only if the cosmic body falls near the shore - at a distance of 10-20 km.

As mentioned earlier, the wind creates waves up to 21 meters high maximum, but they can not be called a tsunami. However, in the event of a sharp jump in atmospheric pressure, meteotsunami.

Human activity can also negatively affect natural conditions.At the same time they talk about the occurrence of artificial tsunamis. This includes various tests in the form of atomic explosions, activation of hydrogen bombs, etc., therefore, they are prohibited in some international treaties.

Classification

Tsunamis are classified according to several criteria, such as the causes of occurrence, the intensity of the phenomenon, the number of affected people. Depending on the origin, tsunamis are divided into 4 types:

caused by underwater earthquakes;
caused by volcanic eruptions;
caused by landslides;
caused by coastal earthquakes.

By the intensity of the waves, their height and strength, these types of elements are distinguished, distinguishing them by a point system:

1 point - you can notice such waves only with the help of special devices. They are considered non-hazardous.
2 points - the coastline is partially flooded.
3 points - medium-intensity waves reach 2 meters. They represent a danger to small vessels, structures on the shore of a reservoir.
4 points - the height of intense waves up to 3 meters. Small vessels such a tsunami can be washed ashore, and then washed into the ocean. Constructions on the coastline suffer mid-level damage.
5 points - especially strong waves of 8-23 meters in height. The degree of destruction depends on the proximity of objects to the coastline. Even heavy vessels are thrown to land.
6 points - a phenomenon of this, the most powerful type, is considered a natural cataclysm. As a result, a large number of people suffer, the coastline is flooded, buildings are almost completely destroyed.

The tsunami classification by the number of victims is represented by 5 groups:

1 - no injuries;
2 - up to 50;
3 - from 50 to 100;
4 - from 100 to 1000;
5 - more than 1000.

Interesting fact: One of the most powerful tsunamis in the Indian Ocean (2004) as a result of an underwater earthquake. Damaged the territory of 11 countries. The waves reached and exceeded the mark of 30 meters. The element moved at a very high speed - it took her only a couple of hours to cover the distance from one coast of the ocean to the other.

Harbingers

Tsunamis belong to natural phenomena that occur suddenly and spread dynamically. But being attentive and observant, you can notice some signals that portend a natural disaster. These include the following symptoms:

Unusual behavior of animals seeking to quickly leave the coastal zone. Water inhabitants try to get to the depths.
Humming aftershocks.
Unexpected tide or ebb, as a result of which the water goes several kilometers towards the reservoir.
In winter, you can hear the sounds of cracking ice, as well as see unusually drifting ice plates in places that are not characteristic of such phenomena.

An underwater earthquake or land event near a body of water should already alert. The same applies to a sharp ebb, which does not occur according to the “schedule”.

Interesting fact: before collapsing on land, the first tsunami wave moves far from the coast. At the same time, the stronger the ocean floor opened, the more powerful the flow of water will be. The wave will return a few minutes after low tide.

Sometimes the destructive tsunami waves are not yet visible, but they can be heard - from a distance they resemble the peals of thunder.

Effects

A tsunami is a truly destructive natural phenomenon, the damage from which is determined by various factors: altitude, speed, direction of the wave, etc. The effects that cause the tsunami are divided into primary and secondary.

Primary Consequences:

The threat is not only waves, but also the strong flow of air that they create. Under their action, the destruction of weak coastal structures occurs.
Affected people.
Flooding of agricultural territories (crop destruction), leaching of the foundation of residential, industrial type buildings.
Destruction of coastal cliffs, ports.
Flushing vehicles offshore and throwing ships on land.

Given the fact that most coastal areas are densely populated for various reasons (including with the aim of attracting tourists), tsunamis cause tremendous damage to these areas. After each flood and its attendant consequences, these sections have to be rebuilt.

Secondary causes are directly related to the destruction of industrial facilities. In this case, we are talking about the consequences of anthropogenic nature. For example, tsunamis damage the integrity of ships, oil storage facilities, and processing plants for various products. They can also cause accidents at nuclear plants. All such emergency situations entail consequences in the form of various environmental pollution and fires.

Why is the sea tsunami not scary?

Tsunamis are dangerous only for coastal areas, bays. In the middle of the sea or ocean, they are not terrible for ships. This feature is explained by the nature and mechanism of the distribution of elements.

The fact is that in the open sea, the height of the tsunami waves does not exceed several meters. At the disposal of the elements there is a huge space, measured in kilometers. Thus, the strength and power of the waves are “distributed” along the entire length of the front. Near the shore, the tsunami, on the contrary, intensifies and reaches maximum power.

What to do in case of tsunami?

The main thing to do after warning of an approaching tsunami is to react as quickly as possible, following some rules. The first thing to do is:

do not panic;
objectively assess the situation;
exit the building, after turning off the electricity and gas;
leave the coastline and not approach the coast closer than 3-4 km (preferably elevated sections).

There may be situations when there are tsunami precursors (earthquakes, low tides, etc.), but no official notification is received. In this case, it is better to be proactive.

People living in potentially hazardous areas should prepare a disaster action plan in advance and adhere to it strictly. It is necessary to warn others of the impending elements.

If time and current conditions allow, it is recommended to take documents, other valuables, water, dry clothes and pack it all in a waterproof bag. Waves can be waited for at least 40 m.

The tsunami sometimes catches up all of a sudden. In this case, there may simply not be enough time for the above actions. Once on the coast at the very epicenter of a natural phenomenon, you should find the strongest structure or tree and grasp it tightly (so as not to be in the water column).

If the waves overtake in the building, it is necessary to go to the upper floor and find shelter. Suitable options are rooms without windows, doorways, corners.

Those who are in the water are recommended to perform the following actions:

get rid of shoes and heavy clothes;
to group
Find a large, reliable item and catch on it.

It is important not to return to shore immediately after the first wave. Tsunamis often approach in the form of a second, third and subsequent waves with even greater force. As soon as a message appears that the threat has passed, a check of the surviving buildings begins.

Protective measures

In order to minimize the effects of the tsunami, a system of protective measures has been developed:

Specialists constantly monitor seismic activity and make short-term / long-term forecasts.
Timely warning of the population with the help of sirens, television and radio broadcasting.
A ban on the construction of buildings along dangerous coasts or the construction of buildings of increased strength.
The construction of hydraulic structures (breakwaters, dams, breakwaters).
Strengthening the coastline by tree planting.
Sending ships to the open sea.
Compilation and dissemination of action plans in the event of a tsunami among local residents, as well as regular exercises.
Preliminary preparation of means and places of evacuation, equipped with everything necessary.
Fire fighting measures.

Tsunami Prediction

Specialists work on long-term and short-term forecasts. Long-Range Forecasting It is a risk assessment for certain territories. What is the probability of a tsunami, speed and wave height, etc.

Short-term or operational forecast allows you to find out about the occurrence of a tsunami when it has actually arisen. Seismologists obtain tremors and, based on this information, decide whether a tsunami is possible and, if so, how dangerous it is. The problem is that disasters arise for other reasons.

Modern instruments and the results of scientific advances make it possible to more accurately predict tsunamis. For example, deep-sea DART devices.

Where are tsunamis most often?

High seismic activity is observed in the Pacific Ocean. For inhabited islands, territories with access to water in this zone, the highest danger threshold is set. This applies to underwater earthquakes. If a tsunami occurs as a result of landslides, then it poses a threat to any coast.

Interesting fact: According to research from various regions, increased attention is paid to Alaska, northern California, South America.

Tsunami study

Most actively, tsunami studies are carried out by specialists from Japan, Russia, the United States, but in general, studies are conducted around the world. The pioneers in this field in the Russian Federation were the academies S. Soloviev and Yu. Israel. They contributed to the creation of a warning system of the impending tsunami in the Far East.

The study of this phenomenon is a complex task. First of all, specialists strive to accelerate the process of tsunami recognition, alert the population, and also expand the list of harbingers of the elements.

The most famous tsunamis in history

The most famous were natural phenomena that caused tremendous damage. Among them, the following tsunamis are worth noting:

Indian Ocean Coast. The seabed broke in 2004, after which waves of 30-meter height were formed. The coasts of Thailand, India, Sri Lanka, and East Africa were affected.

Northeast Japan. The tsunami hit the shore in 2011. Miyagi Prefecture was hit hardest. The height of the waves reached 40 m. Material damage amounted to several hundred billion dollars. There were also accidents at nuclear power plants.

Alaska, Fjord Litui. In 1958, an earthquake and landslide occurred. A huge mass of ice and soil hit the bay from a distance of 1 km. A powerful wave appeared, which quickly reached the opposite shore, reaching more than 500 m.