Tsunami (Meaning and Explanation)

We explain what a tsunami is and what its causes and consequences are. Also, its characteristics and what megatidal waves are.

What is a tsunami?

Tsunamis, also called tidal waves, are waves that move through the ocean at high speed and that, when they reach the coast, can reach up to 30 meters in height.

Tsunamis occur in large bodies of water such as seas and oceans, and are extremely rare in smaller bodies of water such as lakes and lagoons.

They originate from earthquakes that occur in the oceanic crust, which release large amounts of energy. This energy is transmitted to the water and waves are generated that move through the ocean.

Tsunamis occur mainly in the Pacific Ocean, and are less frequent in the Indian and Atlantic Oceans.

Causes of a tsunami

For the most part, tsunamis are caused by earthquakes that occur on the sea floor. These earthquakes produce a sudden movement of the tectonic plates that make up the ocean floor, which generates a large release of energy. This energy is transferred to the water through waves and can cause a tsunami to form.

Less commonly, tsunamis can be caused by eruptions of underwater volcanoes. These eruptions release a lot of energy, which spreads through the water and can form large waves.

Another possible but even stranger cause is the fall of a meteorite into the ocean, which can also generate waves that propagate through ocean water.

Consequences of a tsunami

The most frequent consequences of tsunamis are:

Floods, which are caused by the impact of the tsunami in coastal areas.
The loss of human life and material property as a result of the impact of waves with the coast, floods or rip currents that move people and objects into the sea.
Pollution of fresh water by salt water penetrating inland. This not only affects the availability of drinking water but also significantly changes the salinity of the soil, which can negatively affect its fertility.
The deterioration or destruction of underwater ecosystems near the coast. The impact of waves can put the balance of coastal ecosystems at risk and have a significant impact on the development of the life of corals, algae and other marine species.

How is a tsunami measured?

Tsunamis can be measured in:

Height. It refers to the vertical height that the waves reach when they reach the coast.
Wavelength. Measures the distance between two successive wave crests. The wavelength of a tsunami can be very long, meaning that the distance between two wave crests can be several hundred kilometers.
front length. It refers to the width of the waves produced by the tsunami.

How to prevent a tsunami?

There are various measures that can be taken to prevent or reduce the impact of tsunamis in coastal areas:

Early warning systems. They allow coastal communities to evacuate or prepare for the arrival of a tsunami.
Evacuation plans. They make it easier for people to know what to do in the event of a tsunami warning. In areas that are frequently affected by these natural phenomena, there are safety areas where people can take refuge from the arrival of large waves.
Resilient infrastructure. Retaining walls and protective barriers reduce the impact of waves when they reach the continent.

Warning systems

Since the 1920s, there have been warning systems to prevent tsunamis in territories where tectonic movements usually occur.

In 1949, the “Pacific Tsunami Warning Center” was created in the United States (Pacific Tsunami Warning Center). This is one of the largest tsunami warning systems in the world and covers most of the Pacific Ocean.

A prevention system called CREST (Consolidated Reporting of Earthquakes and Seaquakes) is used on the northwest coast of the United States and in Hawaii. It is a tsunami monitoring system through ocean seismic sensors that was created by the United States Geological Survey.

In addition, there are tsunami monitoring systems in other parts of the world, such as the Indian Ocean Tsunami Warning Center that operates in Australia, or the Su Pacific Tsunami Warning Systemr (SPATS) which includes tsunami monitoring for the coasts of countries such as Chile, Peru and New Zealand.

You may be interested: Hurricane Patricia

Danger of a tsunami

The movement of underwater tectonic plates is the most frequent way in which tsunamis occur. The danger that the tsunami has when it reaches the coast will depend on various factors:

Magnitude of the earthquake. The greater the magnitude of the earthquake, the greater the energy released by the oceanic crust and the greater the amount of energy is transmitted through the water of the oceans.
Hypocenter depth. The hypocenter is the point beneath the Earth’s crust where tectonic movement originates. At greater depths, the chances of a destructive tsunami occurring are lower since much of the energy released is dissipated before making contact with the water.
Seafloor morphology. The presence of underwater canyons, volcanoes or continental shelves can amplify or diminish the force of the tsunami.
Distance from epicenter. The epicenter is the place on the surface of the water, just above the hypocenter. Tsunamis usually lose strength as they move away from the epicenter, so the greater the distance from the coast, the less their impact will be.

Mega tidal waves

Mega tidal waves are large underwater earthquakes that can generate very destructive tsunamis. To be considered a megatidal event, the seismic event must register a magnitude of 9.0 or higher on the Richter scale.

Megatidal events are extremely rare events and do not occur frequently. However, due to their great destructive power, they are the object of constant study and research by geologists and specialists on the subject.

Differences with swells and macareos

What is a swell?

A storm surge is a rise in sea level due to weather conditions such as storms, hurricanes or cyclones.

Storm surge can be very destructive if combined with heavy rain and winds.
The central difference with tsunamis is that they are surface waves and their origin is the wind, not tectonic movements.

What is a macareo?

Macking is a particular form of tidal wave. It is a natural phenomenon that occurs in the ocean and refers to a long, regular tidal wave that moves through the oceans.

Relevant tsunamis in history

Japan Tsunami in 2011

tsunami - japan — The earthquake in Japan lasted six minutes and was the largest that that country has ever suffered.

The Japan tsunami is officially called the “Great East Japan Earthquake,” but it is also known as the Tohoku Earthquake. It happened on March 11, 2011 off the coast of Japan. The earthquake that generated the tsunami had a magnitude of 9.0 on the Richter Scale.

The waves reached a height of 40 meters and caused the death of more than 15,000 people. It was very destructive, among other factors, because the epicenter was located very close to the country’s coasts.

The effects of this tsunami extended to the Californian coast of the United States and Hawaii, where the waves exceeded 3 meters in height and invaded up to 3 kilometers of land. This earthquake, which lasted 6 minutes, was the most powerful that Japan has ever suffered and the fourth largest magnitude worldwide.

Indian Ocean tsunami in 2004

The Indian Ocean tsunami occurred on December 26, 2004 off the coast of Sumatra, Indonesia, after an underwater earthquake measuring 9.1 on the Richter scale.

It affected several countries in the Indian Ocean, including Indonesia, Thailand, Sri Lanka, India and Somalia. It is estimated that around 230,000 people died and millions were affected. The tsunami caused massive damage to coastal infrastructure and destroyed entire cities, ports and fishing communities. Rescue and recovery efforts lasted for months.

References

López Bermúdez, F. (2002). Physical Geography and nature conservation. Geography Papers, 36. https://www.researchgate.net/
Pech, P and Regnauld, H. (1997). Physical geography. Teaching.
Tarbuck, E., & Lutgens, F. (1999). Earth Sciences. An introduction to physical geology. Prentice Hall.