What Is a Tsunami?

Japan Struggles To Deal With Nuclear Crisis And Tsunami Aftermath
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A tsunami is a giant wave (or series of waves) created by an undersea earthquake, volcanic eruption or landslide.

Tsunamis are often called tidal waves, but this is not an accurate description because tides have little effect on giant tsunami waves.

Far out in the ocean, tsunami waves do not get very high, but they move very fast. In fact, the National Oceanic and Atmospheric Administration (NOAA) reports that tsunami waves can travel as fast as a jet plane.

As a tsunami gets closer to land and the ocean depth decreases, the speed of the tsunami wave slows down and the height of the tsunami wave increases dramatically—along with its potential for destruction.

One thing is certain about tsunamis: their strength and behavior are difficult to predict. Once a tsunami makes landfall, the waves can last from five to 15 minutes and do not follow a set pattern. NOAA warns that the first wave may not be the largest. A strong earthquake in a coastal region puts authorities on alert that a tsunami may have been triggered, leaving a few precious minutes for coastal residents to flee. Another sign of an imminent tsunami is when the water retreats far from shore very rapidly - but by then you have even less time to react.  

Most undersea earthquakes or other seismic events do not create tsunamis, which is in part why they are so difficult to predict.

Some Recent Tsunamis Were Devastating

  • The day after Christmas 2004, a violent earthquake struck in the Indian Ocean, off Indonesia. The energy released by the quake set off a tsunami that hit the coasts of Indonesia, Sri Lanka, India, and Thailand. More than 200,000 people perished.
  • In March 2011, a 9.0 magnitude earthquake rocked Japan, sending a massive set of waves on its coastline. Over 18,000 people died; buildings, roads, seaports, and railroads were destroyed, and a nuclear power plant was severely damaged.

Environmental Consequences of Recent Tsunamis

Large tsunamis cause devastating damage to land, often scouring everything down to bare earth, but the death toll and human suffering understandably preempt environmental concerns at the site of the disaster.

Elsewhere, the resulting marine pollution can be observed far distances from the tragedy. When waters are receding from flooded lands, they take with them large amount of debris: trees, building materials, vehicles, containers, ships, and pollutants like oil or chemicals.

Several weeks after the 2011 Japan tsunami, empty boats and pieces of docks were found floating off the Canadian and US coast, thousands of miles away. However, much of the pollution from the tsunami was not so visible: tons of floating plastic, chemicals, and even radio-active material continue to swirl in the Pacific Ocean. Radioactive particles released during the Fukushima nuclear power meltdown worked their way up the marine food chains. Bluefin tuna, which migrate long distances, were found off the coast of California with elevated levels of radioactive cesium. 


Edited by Frederic Beaudry.