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What is a Tsunami?

Last Updated : 13 Sep, 2022
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Tsunami is a Japanese word that sounds like “soo-nah-me,” with “tsu” standing for harbor and “nami” for wave. Tsunamis are waves brought on by the abrupt movement of the ocean’s surface as a result of earthquakes, seafloor landslides, landfalls into the water, powerful volcanic eruptions, or meteorite impacts.

The word “tidal wave,” which was once used to describe tsunami, is now universally avoided because the formation of the tsunami has nothing to do with tides (which are driven by the gravity of the Earth, Moon, and Sun). There are times when a tsunami will also include one or more choppy breaking waves, despite the fact that sometimes they will appear at the coast as a swiftly rising or lowering tide.

What distinguishes tsunamis from other waves?

A wind-generated ocean surface wave is not the same as a tsunami. The passage of a tsunami involves the movement of water from the surface to the seafloor, unlike wind-generated waves in deep water, which only induce water movement near the surface. Contrary to wind-generated waves, this has the interesting effect of causing a tsunami’s pace to depend on the depth of the ocean, with quicker speeds in deeper water. As a result, a tsunami slows down as it gets closer to land and enters progressively shallow water, and the space between each wave crest is smaller. The energy is transferred to raise the wave height because the wave’s overall energy remains constant. The term for this is wave shoaling.

The first wave in a series of waves that make up a tsunami may not always have the largest amplitude. Even the strongest tsunami in the open ocean are often only tens of centimeters or less in height when they are far from the tsunami’s initial genesis zone. There are occasions when higher oceanic wave heights are seen quite near the tsunami-producing zone. The shoaling effect, in any case, can significantly raise the height of open ocean waves as they approach the shoreline, with some tsunamis reaching an onshore height of more than ten meters above sea level. Extreme flooding is more likely to happen close to the source of the tsunami and in areas where the coastline is particularly conducive to the tsunami’s amplifying effects.

Tsunami Characteristics

  • The majority of tsunamis on Earth are modest and non-destructive, making them one of the rarest threats.
  • When a tsunami enters shallow water, its wavelength shortens while the period remains constant, increasing the wave height. Over deep water, tsunami has very long wavelengths.
  • Offshore, tsunamis have a small wave height. This can be as small as a few centimeters or as tall as over 30 meters. Most tsunamis, nevertheless, feature waves that are no higher than 3 meters.
  • It spreads out from the source and covers the entire ocean in all directions.
  • It often consists of a sequence of waves, each lasting somewhere between a few minutes and several hours.
  • These are the tremor-generated waves, not the actual earthquake waves.
  • Because not all tsunamis behave the same way, there is no season for them. Where, when, and how damaging it will be are all unknown. A few miles distant, a tiny tsunami may be very big.
  • Different coasts may be affected differently by one tsunami. Any ocean coast could experience a tsunami at any time.
  • Only if the tremor’s epicenter is below oceanic waters and its magnitude is large enough will a tsunami’s effects be felt.
  • The depth of the water affects the wave’s speed in the ocean. In comparison to deep ocean waters, it is more prevalent there. As a result, a tsunami’s effect is felt greater in the area close to the coast than it is over the ocean.

Interesting Facts about Tsunami

  1. According to scientists, a tsunami with a magnitude of 9 struck the Pacific Ocean in the year 1700, causing significant flooding and devastation in Japan.
  2. Tsunamis can traverse the whole ocean in less than a day and move at speeds of up to 5000 miles per hour without being seen.
  3. Even at heights of less than 30 centimeters, a tsunami can go unnoticed.
  4. The strength of a tsunami wave increases with each successive hit; the first hit rarely has the same impact as subsequent ones.
  5. Tsunamis can move up to 500–800 kilometers per hour, which is almost as quickly as a jet airliner.
  6. Greek historian Thucydides was the first to refer to undersea earthquakes as tsunamis in his work History of the Peloponnese War.
  7. Tsunamis only reach heights of 1-3 feet deep in the ocean, and passing people may not even be aware that one is happening.
  8. Many experts think that 3.5 billion years ago, the earth experienced a tsunami brought on by a meteorite.
  9. Onshore, palm trees are planted because their sturdy trunks are known to withstand tsunamis.
  10. When and where a tsunami is most likely to occur may be predicted by scientists with virtually perfect accuracy. Their estimation is based on calculations such as water depth, earthquake time, travel distance, etc.

FAQs on Tsunami

Question 1: What tsunami was the largest ever recorded?


The greatest tsunami wave ever recorded was almost 1,700 feet tall and occurred in Lituya Bay, Alaska, on July 9, 1958. Five square miles of land were flooded, and tens of thousands of trees were felled.

Question 2: When do tsunamis occur?


In some places, large tsunamis might last for days before reaching their height, which usually happens a few hours after arrival and then gradually fades away. The tsunami period, or the interval between tsunami crests, can last anywhere between five minutes and two hours. Tsunami currents that are dangerous might linger for days.

Question 3: How common are tsunamis?


In the Pacific Basin, there are often two catastrophic tsunamis per year. Pacific-wide tsunamis are a rare occurrence, happening around once every 10 to 12 years. There is no season for tsunamis, and they don’t happen often or frequently.

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