All About Waves of Tsunami

A Tsunami generally occurs due to a sudden shift in the ocean’s tectonic plates, usually due to an earthquake. This shifting of the plates causes the water to rise higher above the level of the ocean. Once the Tsunami waves approach the shore, they slow down but still cause extreme environmental damage. The speed of the Tsunami waves is extremely high.

Formation of Tsunami Waves

Megathrust earthquakes cause a sudden displacement in a seabed sufficient to cause the sudden raising of a large body of water.
As the subducting plate plunges beneath the less dense plate, stresses build-up, the locked zone between the plates give way abruptly, and the parts of the oceanic crust is then upthrust resulting in the displacement of a large column of water vertically.
The tsunami on December 26, 2004, was caused after an earthquake displaced the seabed off the coast of Sumatra, Indonesia.
A marine volcanic eruption can generate an impulsive force that displaces the water column and gives birth to a tsunami.
During a submarine landslide, the equilibrium sea-level is altered by sediment moving along the floor of the sea. Gravitational forces then propagate a tsunami.
Most destructive tsunamis can be caused due to the fall of extra-terrestrial objects on to the earth.

Propagation of the waves

Gravity acts to return the sea surface to its original shape.
The ripples then race outward, and a tsunami is caused.
As a tsunami leaves deep waters and propagates into the shallow waters, it transforms. This is because as the depth of the water decreases, the speed of the tsunami reduces. But the change of total energy of the tsunami remains constant.
With the decrease in speed, the height of the tsunami wave grows. A tsunami which was imperceptible in deep water may grow to many metres high, and this is called the ‘shoaling’ effect.
Sometimes, the sea seems to at first draw a breath, but then this withdrawal is followed by the arrival of the crest of a tsunami wave. Tsunamis have been known to occur suddenly without warning.
In some cases, there are several great waves separated by intervals of several minutes or more.
The first of these waves is often preceded by an extraordinary recession of water from the shore, which may commence several minutes or even half an hour beforehand.

Characteristics of a Tsunami

The wavelength of a deep ocean tsunami can be up to 200 kilometres
Tsunamis are fast in deep waters and slow in shallow waters
Small tsunamis can be destructive because they may carry debris
Tsunamis come in multiple waves
The time difference between one wave and another can be hours
The later waves are usually more destructive
When a tsunami reaches the shore, there is a temporary rise in sea levels, which is called a “run-up”
About 80% of the tsunami waves happen in the Pacific Ocean
Tsunamis can travel from one end of the pacific ocean to the other in just one day.

Effects of Tsunamis

Residents of coastal areas are in serious danger from tsunamis. They emerge out of nowhere and strike the seashore like a water bomb with enormous, powerful waves that are travelling with great speed.
Loaded with enormous energy, the killer waves create havoc by flooding hundreds of metres inland, past the typical high water level.

Difference between ‘tsunami’ and ‘tidal wave’

Tsunamis are usually referred to as ‘tidal waves’ but they are not so. There are a lot of differences between a tsunami and a tidal wave based on various factors:

Cause: A tidal wave is the caused due to the gravitational forces of the sun and the moon whereas tsunamis are caused due to underlying causes like earthquakes, erupting submarine volcanoes or any gas bubble erupting in the sea or ocean.
Location: Tidal waves are noticed mostly in coastal areas. On the contrary, tsunamis can take place in any large body of water if the underlying causes are present there.
Frequency: Tidal waves take place at regular intervals whereas a tsunami has no specific time and can occur at any time if there are favourable conditions (seismic activity) for its occurrence. However, tsunamis are rare.
Intensity: Tidal waves usually do not cause much damage if they are not very high and even if they are high, they can affect only coastal areas whereas a tsunami can travel a long distance and cause extensive damage.

FAQs related with Tsunami Waves

Ques 1. What causes tsunamis?

Ans. Tsunamis are primarily caused by large-scale events that disturb the ocean floor, such as underwater earthquakes, volcanic eruptions, or landslides. These events displace massive amounts of water, generating powerful tsunami waves.

Ques 2. How do tsunamis differ from regular ocean waves?

Ans. Tsunamis differ from regular ocean waves in several ways. They have much longer wavelengths, often stretching across hundreds of kilometers, and higher amplitudes. Unlike regular waves that are primarily influenced by wind, tsunamis are generated by vertical movements of the ocean floor, resulting in their devastating power.

Ques 3. What are the impacts of tsunamis?

Tsunamis can have catastrophic impacts when they reach coastal areas. They can cause widespread flooding, destruction of infrastructure, loss of life, and long-lasting environmental damage. The force and speed of a tsunami can lead to the erosion of coastlines, damage to buildings and structures, and the displacement of communities. Early warning systems and preparedness measures are crucial in mitigating the impacts of tsunamis.

Read Also : Anatomy Of A Wave