What is a Tsunami?

A sign in Alaska warning of the danger of tsunamis.

Tsunamis, also known as seismic waves, are massive bursts of waves that result from sudden motions along the ocean flor. Tsunamis are different from regular waves in that they have a much greater wavelength. Tsunamis go back as far as the earth's history. In fact, tsunamis even captured the attention of Thucydides, a historian from Ancient Greece, who theorized that the origin of tsunamis was related to earthquakes that occurred underwater. The ancient Romans also had a significant interest in tsunamis with one of their most famous historians, Ammianus Marcellinus, writing about tsunamis after the occurrence of a seismic wave in 365 AD that significantly affected the city of Alexandria.

The Causes Of Tsunamis

Sudden motions at the bottom of the ocean floor can be caused by a variety of factors. Earthquakes that occur under the water are one of the main events that result in the formation of a tsunami. In order for an earthquake to produce a tsunami, it needs to have a magnitude of more than 7.0 on the Richter scale. Tsunami-causing earthquakes occur in areas of the world in which bits of the world's crust rub against one another. When the pieces of the earth's crust rub against one another they generate vast quantities of seismic energy which gets released as an earthquake. The immediate aftermath of the earthquake in the case that the epicenter is close to the floor of the sea is the displacement of large amounts of water. The mass of water spreads rapidly in the form of massive waves from the epicenter. Tsunamis that originate from deep oceans grow as they approach regions where the water is shallow.

Tsunamis In History

Tsunamis have occurred for long time throughout history with the first ever recorded history happening in Syria more than 4000 years ago. An earthquake that occurred in 365 BC significantly devastated the city of Alexandria, one of the world's most historic towns. In Ancient Greece, a tsunami happened in 373 BC that devastated the city of Helike which was situated about 1.2 miles away from the sea. In spite of the great distance from the sea, the town was submerged beneath the sea. Japan is one of the places in the world that receives the most tsunamis and the first tsunami in recorded history to affect Japan occurred in 684 BC and affected several regions such as the Kii and Shikoku areas. One of the most damaging tsunamis to impact the world occurred in 2004 within the Indian Ocean. The tsunami was responsible for more than 167,000 deaths in Indonesia and roughly 278,000 deaths internationally. The tsunami caused damage worth nearly $20 billion.

The Impact Of Tsunamis

Tsunamis are some of the world's most catastrophic natural disasters primarily because they cause a massive loss of life. Apart from the loss of life, people are also commonly significantly injured by the tsunamis. Many people lose property of significant value during a tsunami. Tsunamis hinder the economies of various countries as they hamper the growth of industries such as tourism. Since tsunamis affect the coastlines, the number of tourists who visit the beaches dramatically declines.


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