Tsunami – Killer Waves

The word tsunami comes from the Japanese : tsu means harbour and nami waves. A tsunami is a series of ocean waves that can travel over hundreds of kilometres at a very high speed. They are hardly seen in the open ocean, but when they reach the shallow water near the coast they get taller and taller—up to 30 metres. The waves are so powerful that they can destroy everything that gets in their way.

Tsunamis are created by earthquakes on the ocean floor. The earth’s crust is made up of many plates that always move. Where such plates meet, one of them may move on top of the other. When a plate moves upward it pushes the water above normal sea level. That is when a tsunami is born.

The energy of the earthquake creates waves that spread into all directions very quickly. In the open ocean tsunamis can reach a speed of up to 900 kilometres an hour. When a tsunami approaches the coastline it slows down to maybe 50 km an hour. The water has nowhere to go so it piles up—in some cases it gets taller than a ten-story building. It crashes onto the coast and destroys houses, beaches, roads without difficulty.

When the wave enters shallow water, it slows down and becomes taller
Image: Régis Lachaume , CC-BY-SA-3.0, via Wikimedia Commons

Tsunamis cause most damage when an underwater earthquake occurs near a coastal region. The waves can reach the coast within minutes and the population there cannot be warned in time. There is almost no way of escaping. If quakes happen very far from land it may take the killer waves a few hours to reach the coast. People can be warned and get to a safe place .

On the beach people who witness a tsunami approaching will see a great rise and fall of water. Sometimes the water near the beach will completely disappear and a few minutes later the first of the great waves can reach the shore. In some cases tsunamis don’t arrive as one big wave but as a strong flood.

People, especially tourists, often make mistakes when they see a tsunami approaching. Curious crowds stay at the beach and watch the giant waves come in. When they realize how tall these waves are, it may be too late to run. The best thing to do is to try to run as far inland as possible and try to reach high ground.

Many regions around the Pacific Ocean have warning centres and special plans on how to evacuate people when a tsunami comes close. The Pacific Tsunami Warning Centre is located on the Hawaiian islands. It detects the rise of ocean water and underwater earthquakes and reports information to many other stations in other countries. Local governments must then decide what to do.

On December 26, 2004 the world’s most powerful earthquake in 40 years occurred off the coast of Sumatra, Indonesia. The tsunami that it set into motion hit the coastal areas very quickly—during the middle of the Christmas season. Thousands of Europeans were on the beaches of Thailand, Indonesia, Sri Lanka and other islands when the tsunami hit. It is thought that about 280,000 people died . Many coastal villages were wiped out completely

Location of the 2004 Indian Ocean tsunami
Image: Uwe Dedering, CC BY-SA 3.0, via Wikimedia Commons

Village near the coast of Sumatra lies in ruins after 2004 tsunami
Image: U.S. Navy photo by Photographer’s Mate 2nd Class Philip A. McDaniel,
Public domain, via Wikimedia Commons



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