What is a Tsunami?

What is a Tsunami?

They are giant tidal waves that begin from the depth of oceans and violently land on seashores. Underwater earthquakes and volcanic eruptions are the primary causes of tsunamis. Initially, these tidal waves are small where the sea is deep; they can grow up to a hundred feet after reaching shallow waters. 

The largest tsunami ever recorded hit Lituya Bay, Alaska, on July 9, 1958. The massive wave was 1,700 feet tall, and it destroyed everything in a 5 square mile radius. However, the average tsunami wave height is only 3 metres (10 feet). 

What Causes a Tsunami?

Drastic submarine activities such as earthquakes, underwater volcanic eruptions, underwater landslides, glacier calvings, and nuclear tests are the prime causes of a tsunami. However, meteorite fall has also caused tsunamis. Earthquakes and volcanic eruptions are the most frequent causes of tsunamis. 

Tsunamis are as fast as a jet plane in deep waters, but they slow down upon reaching shores. It is nearly impossible to track a tsunami on time. A satellite must be passing over the mega wave to detect it, which is the rarest of the rare occurrence. 

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Characteristics/Features 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

Warning and Prediction of Tsunamis

There is no accurate detection system to identify the occurrence of a tsunami within time, even if the system has the data on the magnitude and location of an underwater earthquake. Tsunami Warning Systems play a key role in evacuating the population within time. 

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Tsunami Warning Systems has Two Major Components 

A sensor network that observes seismic alerts to predict an upcoming tsunami wave. 

• A communication system to relay the warning to the authorities and people

Tsunami Warning Systems have two types 

International 

Such systems cover a vast area across international borders and seas 

• Pacific Tsunami Warning Centre (PTWC) covers the Pacific Ocean
• The National Tsunami Warning Centre (NTWC) covers North America and the Gulf of Mexico
• Integrated Plate Boundary Observatory Chile (IPOC) covers nearly a 600-km seismic area
• Tsunami Early Warning and Mitigation System in the North-Eastern Atlantic, the Mediterranean, and Connected Seas (ICG/NEAMTWS) is a joint warning system established with the help of UNESCO

Regional

Local warning systems also detect a shorter range of seismic activities. The Regional warning systems can relay information in a maximum of 15 minutes. 

Natural Warning Signs of a Tsunami 

• Alarming shaking of the ground
• Receding water from the coast results in ocean floors and reef exposure, which is called a “drawback”
• A thunder sound, coming from the ocean like a jet plane

Mitigation Measures for a Tsunami 

Mitigation measures help in minimising the potential damage caused by tsunamis. Nations like Japan, Indonesia, the Philippines, Alaska, and Chile are the most prone to tsunami destruction. Japan has been proactive in preventing damage. They have installed 39 feet (12 metres) walls at populated coasts. There is still a risk factor of the waves overlapping the walls. 

The 2011 Tōhoku earthquake and tsunami caused the horrific Fukushima Daiichi nuclear disaster. Even though there were protective walls, the waves were large and powerful enough to overrun the barricades. 

Mitigation Measures for Tsunami Waves include 

• Constructing, marking, and publicising evacuation routes
• Construction of evacuation structures
• Public warning
• Educating the people on the risks of a tsunami and the safety tips 
• Issuing of design and construction guidelines to prevent or minimise tsunami damage
• A disaster management plan for tsunami aftermath
• According to tsunami prevention guidelines, reinforcement of existing buildings, houses, and warehouses
• Practising tsunami emergency drills such as moving to higher ground

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Formation of a Tsunami 

An earthquake under the deep ocean causes the chaotic displacement of water. This event marks the beginning of a tsunami. The displaced water takes the form of a wave and moves at a tremendous pace. As this wave moves closer and closer to the shore, its speed decreases but the height increases. A tsunami doesn’t stop after hitting the land; it only ends when its energy is exhausted. In some instances, an earthquake causes underwater landslides, resulting in a tsunami. An underwater volcano causes a tsunami by either erupting or collapsing. The only instance of a tsunami caused by a meteorite was in 1958, in Lituya Bay, Alaska. 

Conclusion 

Tsunamis are natural disasters capable of destroying thousands of trees, homes, buildings, and lives. The characteristics of tsunami waves have paved the way to create modern tsunami warning systems. These systems allow the authorities and people to follow mitigation measures for tsunami waves within a safe time window. We cannot control natural phenomena like earthquakes and volcanic eruptions, but we can bolster our preparedness whenever an imminent tsunami hits our seashores. The best advice for an upcoming tsunami is to seek higher ground or tsunami shelters.