What are the causes of Tsunami?
A series of waves generated in the sea or ocean because of disturbances like earthquakes, volcanic eruptions, meteorite impact, landslides and glacier calvings is called a tsunami. Tsunami is also called a “wave train” as the waves rise in a series that span time periods from few minutes to hours. Tsunami in Japanese language means “harbor wave”. Earlier tsunami waves were known as tidal waves. Now the term is no longer valid as tsunami waves are different from normal waves. Tsunami waves are very long and devastatingly attack the coastal lines across the seas and oceans. Tsunami waves disperse large volumes of water that result in the submergence of several constructions and houses across the coastline. The wave length can be as long as 100 km. As an example, there was a tsunami attack in Chile, South America in 1960. But it travelled almost 17000 km in the Pacific and hit Japan coast.
History of Tsunamis
Greek historian Thucydides made a note in his book “History of the Peloponnesian War” about the causes of tsunami. He is possibly the first person to make an entry about a tsunami. He says, “The cause in my opinion, of this phenomenon must be sought in the earthquake. At the point where its shock has been the most violent the sea is driven back, and suddenly recoiling with redoubled force, causes the inundation. Without an earthquake I do not see how such an accident could happen”.
Longest recorded history of tsunamis is recorded by Japan. In modern times, the worst ever tsunami to hit was in 2004 in the Indian Ocean. Almost 230,000 people were killed in the killer tsunami.
In July 1958, Lituya Bay Alaska, a mega tsunami was hit and it is the tallest tsunami ever hit, wherein waves reached heights of 1720 feet.
In Indonesia in 1883, the eruption of Krakaoa volcano had triggered a series of tsunamis which killed over 36000 people.
CAUSES OF TSUNAMI
When an earthquake hits the ocean, the ocean floor gets deformed and it results in the vertical displacement of water. When the tectonic plates in earth’s crust move abruptly, it results in a tsunami.
Sciorrucks are tsunamis that are caused when underwater landslides occur. It results in dispensing large volumes of water. This type of tsunami occurred in 1958 in Lituya Bay Alaska. Giant waves over 1700 feet struck the coastal areas.
Meteorological conditions like deep depressions cause tropical cyclones. They can also generate meteotsunami in which tides rise several metres above the usual levels. The water displacement results from low atmospheric pressure. Though the result is not tsunami but tsunami like, in which large areas are inundated by water.
Water is literally drawn back exposing those lands that are submerged normally in the first part of the tsunami. This happens because the trough of the wave is in the front and the water propagates outwards.
WARNINGS AND PREDICTIONS
Drawbacks are the first signs of tsunami. If people are around during such times, they should consider the drawback as a warning and should run for higher grounds for shelter. In 2004 Indian Ocean tsunami, a ten year old girl who learnt about tsunamis in the school, saw the drawback and could detect that it could lead to a tsunami. She told her family and her parents could save dozens of lives by warning them. Most of them ran for higher grounds and saved their lives.
After the 2004 Tsunami, several countries erected tsunami warning systems. These warning systems help in warning people before the waves reach the land. Not all earthquakes generate tsunamis and computers are used for analyzing the possibility of an earthquake generating into a tsunami.
Japan is a country prone for earthquakes and tsunamis. They have built tall walls of about 15 feet across the coastal line intending to protect the coastal population. But this precautionary measure did not work out in the case of Hokkaido tsunami. Waves almost 100 feet tall inundated the tsunami wall and submerged several areas.
Tsunami is a calamity which cannot be prevented. Man is not able to overpower nature. Whenever tsunamis hit, only rehabilitation measures can be taken. Science has to go a long way to know more about tsunamis and the warning systems.