What is a tsunami, why does it keep forming in the island country?

GS Paper I and III

News Excerpt:

Recently, Tsunami waves hit several parts of Japan’s coastal areas and urgent evacuation warnings were issued after a 7.6-magnitude earthquake shook the country’s north-central region.

Key Points:

  • People evacuate toward higher ground after a tsunami warning caused by an earthquake in Wajima, Ishikawa prefecture.

What is a tsunami?

  • Tsunami (a Japanese word that means “harbour wave”) is a series of giant ocean waves caused by earthquakes or volcanic eruptions under the ocean. 
  • Reasons For Tsunami: 
    • When an earthquake takes place under the ocean, a large chunk of the ocean floor can suddenly move upward or downward, leading to a sudden displacement of a large volume of water, thereby causing tsunami waves.
    • A similar thing can happen when a volcano erupts in the ocean. The lava flowing out of the volcano displaces the water around it and that water can become a large wave.
  • Big tsunamis usually begin in the deep ocean, where a large volume of water can be displaced.
    • As the wave moves closer to the shore, it grows taller as the ocean becomes shallower.
    • Tsunami waves can be hundreds of feet tall and can travel as fast as jet planes over deep waters while slowing down when reaching shallow waters.
  • However, not all earthquakes or volcanic eruptions lead to tsunamis. 
    • The formation of a tsunami can depend on a host of factors, including the shape of the ocean floor, and the earthquake’s distance and direction.

Why is Japan prone to earthquakes and tsunamis?

  • Japan is situated along the ‘Pacific Ring of Fire’, which is the most active earthquake tectonic belt in the world. 
    • The ‘ring’ refers to an imaginary horseshoe-shaped zone that follows the rim of the Pacific Ocean, where many of the world’s earthquakes and volcanic eruptions occur.
  • Within the Ring of Fire, there are different tectonic belts, including the Pacific Plate, Eurasian Plate, and Indo-Australian Plate, which keep meshing and colliding with each other, causing earthquakes, volcanic eruptions and tsunamis.

Previous Incident of Tsunami in Japan

  • In 2011, Japan was hit by a 9.0 magnitude earthquake and a resulting tsunami which devastated its northeastern coastal communities, killing around 18,000 people and displacing tens of thousands.
    •  Those tsunami waves led to a nuclear meltdown at the Fukushima power plant, causing the most severe nuclear accident since the 1986 Chernobyl disaster in the Soviet Union.


Prelims PYQ

Q. 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 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 which 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.


Mains PYQ

Q. On December 2004, tsumani brought havoc on fourteen countries including India. Discuss the factors responsible for occurrence of tsunami and its effects on life and economy. In the light of guidelines of NDMA (2010) describe the mechanisms for preparedness to reduce the risk during such events. (UPSC 2017)


Book A Free Counseling Session