Tsunamis

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This document was produced in cooperation with the Emergency Management Division of the Washington State Military Department.

A tsunami is a series of destructive waves affecting shorelines. Tsunamis are usually generated by earthquakes. Tsunamis may also be caused by underwater landslides or underwater volcanic eruptions.

Tsunami dangers

  • Tsunami waves can be created by events thousands of miles from our beaches.
  • Tsunami waves can be as tall as 30 feet when they come ashore; 100 feet in extreme cases. They can move inland from several hundred feet to several miles.
  • A tsunami can cause a series of waves that arrive over several hours. Later waves can be larger than the first wave.
  • Tsunamis move faster than a person can run.
  • Tsunamis have enormous power—enough to move rocks weighing several tons, boats and other debris. Homes and other buildings can be destroyed. People can be killed or injured by the force of the water.

Tsunami definitions

The National Oceanic and Atmospheric Administration (NOAA) can issue a tsunami watch or warning within 15 minutes after an earthquake.

Tsunami Advisory

  • An advisory reports a threat of a potential tsunami that may produce strong currents or waves dangerous to those in or near the water.
  • Listen to your radio, NOAA Weather Radio, or TV for updates on the watch.
  • Know well in advance what your safest evacuation route will be.
  • Local officials will determine appropriate actions such as closing beaches, evacuating people, repositioning ships, etc.

Tsunami Watch

  • A watch reports conditions that may cause a tsunami.
  • Listen to your radio, NOAA Weather Radio, or TV for updates on the watch.
  • Know well in advance what your safest evacuation route will be.

Tsunami Warning

  • A warning reports that a tsunami may have been generated.
  • Move to higher ground or inland.
  • If no higher ground is near, go to upper levels of reinforced buildings.
  • Continue to monitor your local radio or NOAA Weather Radio for further information and instructions.
  • Wait for the “All Clear” before you return to the beach or to your home.

What to do at the beach

Immediately head for high ground; do not wait for a warning if:

  • The ground shakes.
  • You hear a siren.
  • The ocean recedes dramatically from the shoreline.

Coastal evacuation signs

Tsunami evacuation route signs have been placed along coastal roadways to indicate the direction inland or to higher ground. In some places, there may be more than one route to safer areas. These routes may be marked with several signs showing additional options for evacuation. You should know the evacuation routes for your area.

Other languages (All files are PDF.)

DOH Pub 821-036
Revised - March 2008
Reviewed annually