[Geography Notes] on Tsunami Pdf for Exam [2024]

The tsunami definition states that “A series of waves triggered by the movement of a large amount of water in a water body, typically an ocean or a large lake”.

The tsunami definition tells us that these are waves so tsunamis are also known as tidal waves. Tsunamis and tides both create inland water waves, but the inland movement of water in the case of a tsunami can be much greater, giving the appearance of an extremely high and strong tide called a tsunami wave.

In this article on tsunamis, we will learn about the causes and effects of tsunamis, types of tsunamis, and more tsunami information.

What is the Spelling of the Tsunami?

Tsunami is derived from the Japanese word “soo-NAH-mee”. The tsunami meaning in Japanese is “harbour wave”. Since in Japanese words, there is no ‘T’. So when spelt the initial ‘T’ is often silent which fits with the phonological rules of English.

So, the correct spelling of Tsunami is “Tsunami” with ‘T’ a silent letter.

How Tsunami Occurs?

Tsunamis may be caused by earthquakes, volcanic eruptions, and other underwater explosions such as detonations, landslides, glacier calvings, meteorite impacts, and other man-made disruptions above or below water.
The movement of a large amount of water or the perturbation of the sea is the primary cause of a tsunami. Earthquakes, landslides, volcanic eruptions, ice calvings, and, more rarely, meteorites and nuclear tests are all accounted for the water displacement.
Earthquakes are the major cause of tsunamis that occur worldwide.
Let us look into a detailed explanation of tsunami causes.

1. The Tsunami Caused By Earthquake

When the seafloor suddenly deforms and vertically displaces the overlying water, tsunamis may occur.
Tectonic earthquakes are a type of earthquake that is related to the deformation of the Earth’s crust. When these earthquakes happen under the sea, the water above the deformed region is displaced from its equilibrium state.
Because of the vertical component of movement involved, a tsunami can be produced when thrust faults associated with convergent or destructive plate boundaries move suddenly, resulting in water displacement.
Tsunamis have a small wave height offshore and a long wavelength, which is why they go unnoticed at sea, creating just a small swell about 300 mm (12 in) above the normal sea level.
When they enter shallow water, they rise in height, a process known as wave shoaling. A tsunami can occur at any tidal state, and coastal areas can be inundated even at low tide.
Examples of tsunamis caused by earthquakes are the Aleutian Islands earthquake in 1946, the Valdivia earthquake in 1960, the Alaska earthquake in 1964, the Indian Ocean earthquake in 2004, the Tōhoku earthquake in 2011.

2. The Tsunami Caused By Landslides

Landslides cause displacements mostly along the shallower sections of the coastline, and the extent of large landslides that hit the water is uncertain.
Water in enclosed bays and lakes has been shown to be disturbed as a result, but no landslide large enough to cause a transoceanic tsunami has ever occurred in recorded history.

3. The Tsunami Caused By Meteorological Conditions

The tsunami caused due to Meteorological changes is called a Meteotsunami.
Rapid changes in barometric pressure, such as those seen when a front passes through, can displace bodies of water enough to cause trains of waves with wavelengths similar to seismic tsunamis, but with lower energies.
These are basically dynamically similar to seismic tsunamis, with the exception that Meteotsunami lacks the transoceanic scope of substantial seismic tsunamis and that the force that displaces the water is maintained over time, preventing Meteotsunami from being modelled as occurring instantly.
Despite their lower energies, they can be strong enough to cause localised damage and loss of life on shorelines where they can be intensified by resonance.

Types of Tsunami

There are three basic types of tsunami that occur worldwide. Let us discuss in detail the types of tsunamis in this article on tsunami.

Local Tsunami

A local tsunami is one that causes damage in close proximity to the event that triggered the tsunami.
The underwater occurrence, which is typically an earthquake that triggers a local tsunami, occurs within 100 kilometres (just over 60 miles) of the land damage that results.
Since the time between the underwater occurrence and the arrival of the tsunami can be less than an hour, and even less than 10 minutes, these tsunamis can be catastrophic.
There is insufficient time to perform a thorough evacuation.

Regional Tsunami

A regional tsunami is described as one that causes damage between 100 and 1,000 kilometres from the source of the tsunami. Outside the 1,000-kilometer perimeter, more contained damages will occur in some cases.
Regional tsunamis have a significantly longer warning time than local tsunamis, arriving between one and three hours after the triggering incident.
Within a 1,000-kilometer radius, one to three hours might not be enough time for people to safely evacuate.

Distant Tsunami

A distant tsunami, also known as a Teletsunami or ocean-wide tsunami, is caused by a strong and devastating occurrence that occurs more than 1,000 kilometres away from landfall.
A distant tsunami may appear to be a local tsunami at first, but it spreads through vast swaths of the ocean basin.
A distant tsunami allows more time to evacuate and flee, but it also occupies a wider area of land and is more likely to cause extensive and widespread damage.

Effects of Tsunami

Till now we have learned about what is a Tsunami and the types of the tsunami. So in this section, we will learn about the effects of the tsunami.
A tsunami’s impact on a coastline can vary from mild to catastrophic. The characteristics of the seismic event that caused the tsunami, its distance from its point of origin, its duration, and, finally, the structure of the depth of water in oceans along the coast that the tsunami is approaching, all influence the effects of the tsunami.
Here let us discuss a few of the catastrophic effects on nature, animals, and humans.

Destruction

When a massive tsunami hits land, the amount of energy and water stored in it will cause massive damage.
Tsunamis inflict damage by two mechanisms: the slamming force of a fast-moving wall of water, and the destructive strength of a large volume of water draining off the ground and bringing a large amount of debris with it, even with small waves.
The initial wave of a large tsunami is extremely high, but it does not cause the majority of the damage. The vast mass of water behind the initial wavefront causes the majority of the damage, as the sea level continues to rise rapidly and floods the coastal region.
The strength of the waves, the never-ending crashing water, is what causes destruction and death. A tsunami’s huge breaking waves will kill everything in their way as they pound the shoreline.
Tsunami waves wreck everything in their path: boats, houses, bridges, vehicles, trees, telephone lines, power lines, and just about everything else.
If the tsunami waves have swept away the shoreline’s infrastructure, they will proceed inland for several miles, sweeping away more trees, houses, vehicles, and other man-made objects.
Some tsunamis have also made some of the small islands unrecognisable.

Death

The cost of human life is one of the most significant and destructive consequences of a tsunami since surviving a tsunami is virtually impossible. Tsunamis claim the lives of hundreds of thousands of people.
Before a tsunami hits the ground, there is very little warning. When the water flows toward the shore, there is no time to plot an escape path.
People who live in coastal areas, cities, and villages do not have the luxury of time to flee. The tsunami’s strong force causes instant death, most usually from drowning. Another cause of death is buildings collapse, electrocution, and fires from gas, broken tanks, and floating debris.

Disease

In tsunami-affected areas, the disease could spread due to flooding and polluted drinking water. When water is stagnant and polluted, illnesses like malaria will spread.
Since it is difficult for people to remain healthy and diseases to be treated in these environments, infections and illnesses will spread rapidly, resulting in more deaths.

Environmental Impacts

Tsunamis not only kill humans, but also wipe out insects, livestock, plants, and natural resources.
The landscape is changed by a tsunami. It uproots trees and plants, as well as animal habitats including bird nesting sites.
Drowning kills land animals, and waste kills sea animals when toxic substances are washed into the sea, poisoning marine life.
The environmental impacts of a tsunami include not just the landscape and animal life, but also the man-made elements of the climate.

More Facts About the Tsunami

The most dangerous tsunami recorded till now is the Boxing day tsunami, also known as the Indian Ocean tsunami with at least 2,30,000 people killed or missing in 14 countries bordering the Indian Ocean, it was one of the worst natural disasters in human history.
The most recent tsunami is the tsunami 2020 which occurred on the island of Samos (Greece) and the Aegean coast of the Izmir region (Turkey) on 30 October 2020. This significant tsunami was triggered by an earthquake of magnitude 7.0 Mw.
Some zoologists claim that some animals can detect subsonic Rayleigh waves generated by an earthquake or tsunami. Monitoring their actions, if done correctly, may provide an early warning of earthquakes and tsunamis. The proof, on the other hand, is debatable and not generally accepted.
About 80% of Tsunami occur in the Pacific Ocean, “Rings of Fire”.
The first wave of Tsunami is not the strongest. However, the successive waves are stronger and bigger.
Tsunamis can travel up to the speed of 805 km/hrs or 500 miles almost as fast as a jet plane.
The US states like Hawaii, Alaska, Oregon, California, and Washington are at the highest risk of Tsunami.
If anyone is caught by a Tsunami wave, it’s better to not swim, instead, he must grab an object and let the wave carry him.
Tsunamis can travel throughout the ocean with minimum energy loss.
Hawaii is always at risk of a Tsunami- It gets hit by one each year and seven in every seven years. In 1946, Hawaii got hit by the biggest tsunami wave at Hilo Island. The reported height of the wave was 30ft and the speed was 500mph.
In 2004, an earthquake caused a tsunami in the Indian Ocean with the energy of 23000 atomic bombs. After the earthquake, 11 countries were slammed by the radiation emitted from the epicentre. The total death toll was 283000.

Tsunami Safety

A Tsunami becomes dangerous when it approaches land. Its speed decreases from 30mph to 20mph when it enters shallow water near coastlines. The height increases, wavelength decreases, and the currents intensify. Tsunami warnings come in various forms. Tsunami warning centres broadcast warnings through local radio and television, weather radios, wireless emergency alerts, and social media. They may also be received by outdoor sirens, text message alerts, local officials, and telephone notifications.

It is better to recognize natural tsunami warnings instead of waiting for an official warning. These include long and strong earthquakes, a loud sound (similar to train or aeroplane) coming from the ocean, a sudden rise or fall in the sea level not related to the tide. Both natural and official warnings are equally important. One should be prepared to respond quickly to these warnings.

One can move to a safe place by following the evacuation signs. If an individual is unable to do so, then he must go to high ground or far away from the coastlines.

When tsunamis strike land, their height is less than 10 feet, but in some cases, it can exceed 100 feet near their source.

A tsunami can come to the shore like a wall of turbulent water or a fast-rising flood. Moreover, a huge tsunami wave can destroy low-lying coastal areas to a large extent.

Rushing water from floods, waves, and rivers is highly powerful. It can wash off everything coming on their way.

Tsunamis are destructive due to their volume and speed. They become more dangerous when they return from the sea carrying people, objects, and debris with them. Therefore, people are advised to stay out of the tsunami hazard zones until the conditions come under control.