Tsunami Basics

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Inundation at Pago Pago, American Samoa, from the 2009 Samoa tsunami. Image Credit: NOAA/NGDC
Inundation at Pago Pago, American Samoa, from the 2009 Samoa tsunami. Image Credit: NOAA/NGDC

A tsunami is a series of waves formed in a body of water by the sudden displacement of the entire water column. Most large tsunamis are caused by undersea earthquakes, though landslides, volcanic eruptions, explosions, and even meteorite impacts can also cause them. Tsunamis commonly appear on shore as a rapidly receding tide or rapidly rising flood. Tsunamis sometimes provide natural warning signs to people living on coasts, especially close to the tsunami-causing event, such as a rapidly receding tide prior to the waves' arrival. Global monitoring systems also provide critical early warning to coastal populations.[1]

Why do tsunamis matter?

Tsunamis can be highly destructive, causing extensive loss of life and property damage. They have killed more than 350 people on the coast of the United States since 1946, with losses exceeding half a billion dollars.[2] Even larger tsunamis, like the ones that devastated Chile in 1960, Japan in 2011, and Indonesia in 2004, have hit the U.S. Pacific coastal states in the past and could hit them again.

How can geoscience help inform decisions about tsunami hazards?

Tsunamis can’t be prevented, but scientists use earthquake information, tide gauges, and tsunami detection buoys to issue early warnings and give people time to evacuate. Others study records of prehistoric tsunamis left in the geologic record along coasts. These studies help determine the probability of tsunamis on different coastlines, leading to better hazard planning and preparedness. Some geoscientists study the shape and topography of coastal regions to determine the areas likely to be flooded during a tsunami of a given size, which helps to further refine hazard mitigation and evacuation plans.


1Pacific Tsunami Warning Center, http://ptwc.weather.gov

2NOAA/WDC Tsunami Event Database, www.ngdc.noaa.gov/nndc/struts/form?t=101650&s=70&d=7

Learn More

Introductory Resources

  • About Tsunamis (Webpage), International Tsunami Education Center
    In-depth discussion of tsunamis, their causes, and tsunami preparedness for a non-expert audience.
  • Preparedness and the Tsunami Resilient Community (Webpage), National Oceanic and Atmospheric Administration
    Links to national, state, and international tsunami preparedness and response programs.

Resources for Educators

Frequently Asked Questions

American Geosciences Institute
National Oceanic and Atmospheric Administration