The mighty waves ruling the ocean, tsunamis are not larger waves lapping against the shore. They are tidal titans, sparked into existence by monumental disturbances deep down the sea. But how do tsunamis form?

Get an in-depth answer in this fin-tastic article. 

What is Tsunami

A tsunami is a series of large waves induced by volcanic eruption, underwater explosion or massive earthquakes in a water body like the ocean. Deep in the sea, tsunamis are low and long, but as they reach the shore where water gets shallower, they slow down to get extensive and turn into massive mighty water walls, namely tsunami – the marine mayhem. 

Would you be astonished if we say that these seafloor sweeps can get as high as 35m or even higher – same as a 10-storied building? However, the most frightening attribute of a tsunami is its wavelength. The longer the wavelength, the farther inland the wave can inundate. 

For a storm-induced large wave, the wavelength can reach up to 150 meters, causing the energy to be dissipated soon after it hits the shore. For a tsunami, the wavelength can be as high as 1,000 kilometers, allowing the wave to encompass much farther inland. The result is a mayhem accompanied by massive floods and death of people.  

Where do Tsunamis Occur?

You will see tsunamis mostly originated in the “Ring of Fire” – a tectonic plate in the basin of the Pacific Ocean where a string of earthquakes and volcanic eruptions occur. According to the study of the US NOAA Tsunami Program, more than 80% of tsunamis hitting the Earth occurred in the Ring of Fire.

The earthquake that shook the coast of Sumatra, Indonesia, with a magnitude of 9.1 on the Richter scale, caused the most destructive tsunami in world history. It reached a height of a staggering 50 meters, wrecking havoc over an area that extended 5 kilometers from the coastline and killed more than 230,000 people. 

Do you know that tsunamis don’t strike the same place twice? 

How Fast is a Tsunami?

While the speed of a normal wind-forced wave is around 90kmh, for a tsunami wave, the speed is an incredible 970kmh! Sometimes, even before the mighty waves sweep the shore, water from nearby beaches and harbours starts getting sucked up due to the vacuum effect induced by the tsunami. In a minute or so, a big wave blasts onto the shore and the destruction continues for the next couple of hours! 

Can You Predict a Tsunami?

A tsunami can be incredibly destructive, devastating coastlines with mighty towering waves that inundate inland, demolish infrastructure, and claim countless lives. The aftermath can be even more catastrophic that disrupts usual activities of the affected community, leaving lasting socio-economical effects. 

However, the unpleasant truth is that a proper scientific measure to predict an imminent tsunami is yet to be discovered. 

How do tsunamis form?

Here’s how one of Earth’s most destructive forces came to be, in five steps.

Activation

A tsunami starts with massive underwater disturbance, such as an earthquake, landslide or volcanic eruption, far offshore. The earthquake shifts the seabed all of a sudden causing the water to lift up. This is what a tsunami wave starts with. 

Build   

As we have stated, the initial wave starts slow and gets bigger and bigger as water gets shallower. At the inception point of a tsunami wave, it can hardly be noticed with a height of only 30 cm. But as time passes, the marine monsters get mightier traveling at a velocity of over 800km per hour. Even starkly, two successive wave crests are spaced around 100km, whereas this distance is only 100m for a normal wind-forced wave. 

Formation

A tsunami wave consists of a trough and peak. Sometimes the wave gets even more fierce when there appears the drawback effect. The drawback effect is when the trough hits the land first, creating a deceptive effect that makes the wave appear to recede much farther than usual. The drawback effect lasts for around six minutes after which the peak (the real tsunami) makes its fiery entrance, startling and posing risk to those unprepared.

Approach

The tsunami waves approach the shallower water and slow down, losing its strength due to friction with the seafloor. As the wave crest reaches shallower water, friction with the seabed causes it to slow down. The waves trailing these slower waves are relatively faster and begin to accumulate behind them, driving the massive waves forward and making them even more formidable. Do you remember that six minutes of suspense? During this time, the height of the wave crest keeps rising. 

Impact

Tsunamis typically resemble rapidly rising tides rather than breaking wave crests. They can inundate extensive areas, washing away buildings and posing a significant threat to the lives of people and animals. 

Causes of Tsunami

Certain environmental events trigger tsunamis. Some of the causes of tsunamis are: 

• Earthquakes: Underwater earthquakes – seismic events caused by the movement of tectonic plates – are the main culprits behind tsunamis – the liquid leviathans. Tectonic plates are large areas of the Earth’s crust that rest upon the semi-fluid layer of the mantle. Earthquakes shake the Earth’s surface when these plates move away, subduct or collide into other plates. This sudden shake in the seabed, if the magnitude is 7 or above in the Richter scale, displaces a huge volume of water, causing it to radiate outward from the epicenter. This is how earthquakes cause tsunamis – the oceanic outbursts.    
• Volcanic Eruptions: During a volcanic eruption, underwater water gets exploded much like an underwater earthquake. This super powerful explosive force pushes the water away from the volcano and generates a string of mighty waves forming tsunami. Even worse, severe volcanic eruptions can result in landslides into the seawater. This sudden fall of a massive amount of land into the water causes seawater to displace and turn into tsunami waves. If the pyroclastic flow discharged from a volcano, forcefully gets into the seawater, it creates mighty waves that form tsunamis. Pyroclastic flow is  a hot (typically >800 °C, or >1,500 °F )mixture made up of magma, ash and volcanic matter swiftly discharged from a volcanic vent or disintegrating flow front.  In 1883, the world witnessed the destructive events in human history when a tsunami hit Indonesia hard and wreaked havoc. The reason behind this destruction was the volcanic eruption of Krakatoa. 
• Meteorite Impacts: Although rare, near-earth objects, for example comets or asteroids, if collide or explode above the sea, can form watery whirlwinds, what we call tsunami.