Go to content Go to menu

How Tsunamis are Formed


Tsunamis are a massive dark wall of water.  The name comes from the Japanese 'tsu' meaning harbour and 'nami' meaning wave.

Tsunamis are usually formed by undersea earthquakes and volcanic eruptions.  People call them tidal waves but this is incorrect because it has nothing to do with the tides. 

Tsunamis usually occur near the subduction zone when a tectonic plate slips under a continental plate forming an earthquake.  The continental plate flips up and pushes the water causing a wave.

When the wave begins in the opensea you couldn't tell if it is wind generated wave or a tsunamis.  Tsunamis in the open sea are very small but gradually get faster.  The waves are usually spread far apart sometimes for hundreds of miles.

As the wave approaches the shore it slows down, then the wave bunches and squeezes together.  The tsunami gradually grows.  It is a towering wall of water.

As the wave hits the shore it swallows up the land and surrounding area and causes devastation and damage.

Tsunamis are described to be creatures of the open ocean, trains of giant waves that can travel 500mph to 600mph or as fast as a jet.  The unfortunate long lasting effects of a tsunami and the huge damage that it causes can take many years of recovery.


Eight Most Destructive Tsunamis

Aug. 16, 1976: A tsunami generated by a Earthquake on Mindanao in the Philippines killed between 5,000 and 8,000 people in the Moro Gulf region.

March 28, 1964: A magnitude 8.4 earthquake in Alaska generated tsunamis that caused damage in southeastern Alaska, in Vancouver Island, British Columbia, and in the states of Washington, California and Hawaii. More than 120 people died. The worst effected area was Crescent City, California, where waves reached as high as 20 feet destroyed half of the waterfront business district. Eleven people lost their lives there. Extensive damage was reported in San Francisco Bay and at the marinas in Marin County and at the Noyo, Los Angeles and Long Beach harbors.

May 22, 1960: The largest earthquake — magnitude 8.6 — of the 20th century occurred off the coast of south central Chile. It generated a Pacific-wide tsunami, which was destructive locally in Chile and throughout the Pacific Ocean. An estimated 2,300 people were killed in Chile. Waves damaged the waterfront in Hilo, Hawaii, and killed 61 people.

Nov. 4, 1952: A strong earthquake off the coast of Russia's Kamchatka Peninsula generated a great, destructive Pacific-wide tsunami. Its waves struck the Kamchatka Peninsula, the Kuril Islands and other areas of Russia's Far East. Considerable damage and loss of life was caused. There was also damage in Hawaii, Peru and Chile.

Jan. 31, 1906: A strong tsunami struck the coast of Ecuador and Colombia, submerging half of Tumaco, Colombia, and washing away half of a nearby island. The death toll has been estimated at between 500 and 1,500.

Aug. 13, 1868: A massive wave struck Chile, carrying ships as far as three miles inland at Arica. Deaths totaled 25,000 or more.

April 2, 1868: A locally generated tsunami swept over the tops of palm trees and claimed 81 lives in Hawaii.


This is one of the most destructive and devastating Tsunamis in modern history


On the morning of Sunday, 26 December 2004, there was a severe earthquake in the Indian Ocean off the coast of northern Sumatra, Indonesia. The earthquake measured 9.0 on the Richter scale and was followed by aftershocks ranging from 6.3 to 7.0. The underwater earthquake resulted in a powerful tsunami. The wave travelled quickly under the ocean, building to a wall of water up to 10 metres high when it reached the shallow coastal waters causing massive destruction when it landed. Without effective warning people did not know about the the raging tsunami. Many people died  or were seriously injured. People were lucky to be alive. Im sure people won't forget