On Monday, the Japan Meteorological Agency issued tsunami warnings for the coastal prefectures of Ishikawa, Niigata and Toyama of tsunami waves after a severe earthquake.
The word “tsunami” is borrowed from the Japanese language and is composed of two Japanese words: “tsu” (meaning port) and “nami” (meaning wave). The meaning of the word is “harbor wave.”
Earthquakes in the seas and oceans
A tsunami, or tsunami, such as the one Japan warned about today, occurs as a result of a series of huge waves resulting from underwater disturbances for many reasons, most notably earthquakes.
Among the favorable conditions for the emergence of a tsunami is that the earthquake be strong. The magnitude of the Japanese earthquake reached 7.5, according to estimates by the US Geological Survey, and 7.6, according to the Japan Meteorological Agency.
Tsunami waves, resulting from seismic activity from top to bottom of the ocean mass, reach hundreds of meters in height and their strength increases every time they collide with the sea floor.
At the starting point, the tsunami generates only small, very spaced waves because the huge masses of water moved by the earthquake travel deep to the bottom, unlike normal waves that are limited to the surface of the water.
As tsunami waves approach the coast at a speed of approximately 800 km/h, water rises from the ocean floor, concentrating the energy driven by the tsunami. The speed of the waves slows down, they converge, and their height increases significantly, as they can reach more than twenty meters.
The Japanese Meteorological Agency warned of the possibility of tsunami waves reaching a height of five metres, but then reduced this forecast to three metres.
The tsunami wave, since it loses a little of its energy, can spread over large areas, reaching coasts thousands of kilometers away.
In 1960, an earthquake measuring 9.5 on the Richter scale struck Chile, causing a devastating tsunami that reached the coast of Japan.
On Monday, cities in the Russian Far East, including Vladivostok, located on the other side of the Sea of Japan, issued a tsunami alert.
The main countries bordering the Pacific Ocean coordinate their monitoring in anticipation of the dangers of these waves. The Tsunami Warning Center collects information in Hawaii, United States.
other reasons
Although many tsunamis occur after an earthquake, there are other possible causes, including submarine erosion that is sometimes caused by earthquakes, as happened in Papua New Guinea in 1998 (2,000 dead), and a volcanic eruption, as happened in Krakatoa, the small island between Java and Sumatra (36,400). killed in August 1883), or a meteorite falling into the sea.
Light tides may also occur due to phenomena related to weather conditions.
On December 26, 2004, a tsunami swept the coasts of about ten countries in Southeast Asia, killing 220,000 people. Its power is equivalent to about 23,000 atomic bombs like those dropped on Hiroshima, according to the US Geological Survey.
In March 2011, Japan was exposed to one of the worst disasters in the modern era, as a nine-magnitude earthquake struck near its northeastern coast, resulting in tsunami waves, and claiming 18,500 people dead or missing.
Tsunamis are not limited to the Pacific Ocean. In the past, the Atlantic Ocean and the Mediterranean Sea witnessed a sea tide, as reported by the British historian Ammianus Marcellus, who witnessed the earthquake in the city of Alexandria (Egypt) in the year 365.
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