Tsunami, Meaning, Characteristics, Causes, Impacts

Tsunamis are among the most destructive natural phenomena, causing widespread destruction and loss of life. They are a series of powerful ocean waves triggered by large-scale disturbances on the ocean floor. These waves travel at high speeds across oceans, often unnoticed in deep waters, but grow significantly in height as they approach coastal areas, causing catastrophic destruction.

The 2004 Indian Ocean tsunami is a grim reminder of its destructive potential. Thus, understanding tsunamis, their causes, characteristics, and impacts is essential to developing effective response and mitigation measures.

What is a Tsunami?

A tsunami is a series of massive waves produced by an underwater disturbance typically linked to earthquakes that happen beneath or close to the ocean. The Japanese words "tsu" (which means harbour) and "nami" (which means wave) make up the word "tsunami".

• Unlike normal waves, which are caused by the wind and have short wavelengths, tsunamis are caused by geological events, such as earthquakes, underwater volcanic eruptions, landslides, or even asteroid impacts. They have extremely long wavelengths and can travel at high speeds across ocean basins.
• With waves arriving every 5 to 60 minutes, tsunamis can attack the shoreline and be dangerous for hours. Tsunami waves frequently resemble walls of water. Tsunamis can occur at any time of day or night.

Tsunami Characteristics

Tsunamis exhibit unique characteristics, including shallow-water classification due to long wavelengths, extended periods of 10 minutes to 2 hours, jet-like speeds in deep water, multiple waves, and dramatic shoaling effects near coasts.

• Shallow-Water Waves: Tsunamis are classified as shallow-water waves due to their extremely long wavelengths, often exceeding 300 miles (500 km), unlike wind-generated waves that span only 100–200 meters.
• Long Period: The time interval between tsunami waves, known as the period, ranges from 10 minutes to 2 hours, far longer than typical ocean waves, which have periods of 5–20 seconds.
• High Speed: In deep water, tsunamis travel at speeds of up to 550 mph (890 km/h), comparable to a jet aeroplane, enabling them to traverse entire ocean basins within hours.
• Series of Waves: A tsunami is not a single wave; rather, it consists of multiple waves that arrive in intervals. Often, the first wave is not the most destructive, and larger waves may follow, making tsunamis unpredictable.
• Shoaling Effect: As tsunamis approach shallow coastal waters, their speed decreases while wave heights increase significantly, transforming barely noticeable waves into towering surges.
• Energy Conservation: Due to their long wavelengths, tsunamis lose minimal energy during propagation and maintain their strength over vast distances, making them a transoceanic threat.

Tsunami Causes

Tsunamis arise from significant disturbances in the ocean caused by earthquakes, landslides, volcanic eruptions, or rare asteroid impacts. These forces displace massive water volumes, generating waves that devastate coastal regions.

Earthquakes

Tsunamis are caused by movements along fault zones at plate boundaries—areas where tectonic plates interact. Subduction zones, where one plate slides beneath another, produce the strongest earthquakes. For a tsunami, an earthquake must be under the ocean, shallow (under 70 km deep), have a magnitude above 6.5, and trigger vertical seafloor movement.

Landslides

A landslide near the coast can push a lot of water into the water, disturb it, and cause a tsunami. When the material loosened by the landslide moves violently and pushes the water in front of it, underwater landslides can also cause tsunamis.

Volcanic Eruption

Violent eruptions caused by volcanoes, though rare, can trigger destructive tsunamis by displacing large volumes of water. The 1883 Krakatoa eruption caused massive waves up to 135 feet high, devastating Java and Sumatra, destroying coastal towns, and claiming 36,417 lives in one of history’s deadliest tsunamis.

Extraterrestrial Collision

Tsunamis caused by asteroid or meteor impacts are extremely rare but catastrophic. A large asteroid striking an ocean, like the Atlantic, could displace immense water, creating massive waves capable of destroying coastal cities and impacting regions as far as the Appalachian Mountains.

How Does a Tsunami Occur?

A sudden geological event, such as an earthquake or volcanic eruption, displaces a large amount of water and sets off a series of waves. In the open ocean, these waves spread rapidly across vast distances. Due to their long wavelengths, they may go unnoticed, even by ships.

• As the waves reach shallow coastal waters, they slow down due to friction with the seafloor. This compression causes the wave height to increase dramatically.
• The powerful waves crash onto the shore, often causing massive flooding. The water eventually withdraws, only for subsequent waves to strike, causing repeated surges and destruction.

Tsunami Risk Zones

All oceanic regions of the world can experience tsunamis, but the Pacific Ocean and its marginal seas experience much more frequent large, destructive tsunamis because of the many large earthquakes along its margins. 

Tsunami Effects

Tsunamis can have varying effects on coastlines, depending on the event's characteristics, distance from origin, magnitude, and bathymetry (the depth of water in oceans) configuration. Small tsunamis, which are non-destructive and undetectable without specialised equipment, occur daily due to minor earthquakes and other events and are unnoticeable.

• Loss of Life and Property: The intense force of tsunami waves can obliterate entire communities, causing significant loss of life and property. The 2004 Indian Ocean tsunami killed over 230,000 people across multiple countries.
• Disease: In tsunami-affected areas, flooding and contaminated drinking water can spread disease. Whenever water is stagnant and contaminated, diseases like malaria can develop. Because it is difficult for people to maintain good health and treat illnesses, infections and illnesses can spread quickly, increasing the number of fatalities.
• Environmental Impacts: Tsunamis not only cause human deaths but also significantly reduce the number of insects, animals, plants, and natural resources. They alter the landscape, destroy animal habitats, and release harmful chemicals into the sea, causing land animals to drown and aquatic animals to die. 
• Cost: The reconstruction and clean-up after a tsunami is a significant financial burden, involving the replacement of infrastructure, demolition of unsafe buildings, and clearing of rubbish. The financial cost of a tsunami could be millions or billions of dollars, representing a significant portion of a nation's GDP.
• Psychological Effects: Psychological issues that affect tsunami victims frequently last for days, years, or even their entire lives. WHO found that survivors of the Sri Lankan tsunami in December 2004 had post-traumatic stress disorder (PTSD); 14% to 39% of these were children.

Tsunami Risk, Hazard & Mitigation Measures

Tsunami risk and hazard mitigation involve proactive measures, such as advanced early warning systems, evacuation planning, public awareness initiatives, and natural barriers, to minimize destruction, safeguard lives, and enhance resilience in vulnerable coastal areas.

• Early Warning Systems: The establishment of systems like the Indian Ocean Tsunami Warning and Mitigation System (IOTWS) provides early alerts to vulnerable regions. Countries prone to tsunamis have advanced sensors, seismographs, and tide gauges to detect and monitor seismic activity and water levels.
• Evacuation Plans and Infrastructure: Coastal communities implement evacuation routes and shelters to ensure swift and safe movement in the event of an alert. Building regulations often require structures in tsunami-prone areas to withstand wave impact.
• Public Awareness and Education: Educating the public on tsunami warning signs, such as the drawback phenomenon, and conducting regular drills significantly improve survival rates. Japan, a country highly susceptible to tsunamis, has extensive public awareness programs.
• Natural Barriers: Mangroves, coral reefs, and sand dunes help reduce tsunami impact by absorbing wave energy before it reaches populated areas. Coastal reforestation projects can serve as natural tsunami barriers.

Tsunami UPSC PYQs

Question 1: The 2004 Tsunami made people realize that mangroves can serve as a reliable safety hedge against coastal calamities. How do mangroves function as a safety hedge? (UPSC Prelims 2011)

(a) The mangrove swamps separate the human settlements from the sea by a wide zone in which people neither live nor venture out.

(b) The mangroves provide both food and medicines that people are in need of after any natural disaster.

(c) The mangrove trees are tall with dense canopies and serve as an excellent shelter during a cyclone or tsunami.

(d) The mangrove trees do not get uprooted by storms and tides because of their extensive roots.

Ans: (d) 

Tsunami FAQs

Q1. What is called a tsunami?

Ans. A tsunami is a series of powerful ocean waves caused by the sudden displacement of a large volume of water, typically due to underwater earthquakes, landslides, or volcanic eruptions.

Q2. What is the 3 biggest tsunami ever? 

Ans. The three biggest tsunamis in recorded history were the 1958 Lituya Bay Tsunami, the Lisbon Earthquake and Tsunami of 1755, and the 2004 tsunami in the Indian Ocean.

Q3. How big was the 2004 tsunami?

Ans. The 2004 Indian Ocean tsunami reached heights of up to 30 meters (100 feet) in some areas and affected 14 countries. It caused widespread devastation and over 230,000 deaths.

Q4. What causes a tsunami?

Ans. Underwater earthquakes primarily cause tsunamis but can also be triggered by landslides, volcanic eruptions, glacier calvings, and, rarely, meteorite impacts in large bodies of water.

Q5. What is the original name of tsunami?

Ans. The term "tsunami" comes from the Japanese words "tsu" (harbour) and "nami" (wave), literally meaning "harbour wave",