Tsunamis: Be prepared, not scared

Washington State has the second-highest tsunami risk behind Hawaii because of its close proximity to the tectonic plates, crustal faults, and large subduction zone. But DNR scientists have created materials to educate Washington residents of these risks.

Tsunamis in Washington

Since 1700, Washington has experienced multiple tsunamis that were generated from earthquakes caused by the tectonic plates off the coast.

When an earthquake hits, scientists expect a tsunami to land on Washington’s coast within 15 minutes of the initial strike. Two hours and 30 minutes later it is projected to hit the Tacoma waterfront after passing through the Strait of Juan de Fuca.

Washington faces danger from both distant-source earthquakes and other natural disasters.

In 1964, a magnitude 9.2 earthquake in Alaska’s Prince William Sound produced a tsunami with 12-foot waves that flooded Washington’s coastal towns, even sweeping away a bridge over the Copalis River.

Copalis River bridge
Large waves generated by the 9.2 magnitude Alaskan earthquake in 1964 destroyed this bridge in Washington State.

Several of Washington’s largest historic tsunamis were triggered by landslides, such as the 1980 tsunami produced by the Mount St. Helens eruption in Spirit Lake, and the Hat Island tsunami that buried an entire village in the 1820s.

Additionally, eastern Washington faces tsunami hazards, as multiple landslide-induced tsunamis have been recorded in Lake Roosevelt. 

Cascadia Earthquakes

The last Cascadia Earthquake, was recorded 320 years ago in 1700, it shook Washington, and surrounding states, and even Japan with a 9.0 magnitude. Cascadia subduction zone earthquakes occur every 300-600 years when the larger North American tectonic plate is pushed upwards by the Juan de Fuca plate.

Scientists at the Department of Natural Resources (DNR), have put together tsunami evacuation maps and detailed video simulations illustrating the path, intensity, and effects on surrounding areas the next Cascadia Earthquake-induced tsunami is expected to have.   

Understanding Tsunamis

Many tsunamis are generated from the force of tectonic plates thrusting together. The energy that is emitted from this collision reverberates into the water creating a surge that forms large swells of fast moving water.

The greater the depth of water, the faster the water moves, reaching speeds up to 500 mph, the equivalent of a jet plane. As it reaches land, the water becomes shallower. It will slow to speeds of 20 to 30 mph but that is still faster than humans are able to run.

Unlike wind-driven waves, tsunami waves have greater wavelengths allowing them to maintain their force as they move inland, ultimately creating more potential for damage. Flooding from a tsunami wave can last for as short as several minutes up to multiple hours. This is the reason tsunami experts warn that the first wave may not be the most dangerous. In fact, it is the following waves that people should beware.

What we need to know!

All this being said, how should we prepare? Below is a list of preparedness tips, resources, and helpful information to make sure you’re ready when you feel the earth shake.

  1. Be informed: sign up for text alerts from local government and emergency alert stations. Look for signs when you visit coastal cities.
  2. Know your surroundings: if you are near the coastline, know where you can evacuate to higher ground.
  3. Know your evacuation route: if possible, identify multiple evacuation routes in case one is not accessible. You can check for evacuation routes in your area here.
  4. Plan ahead: if you are visiting the coast, ask your hotel staff what their evacuation route is. Likewise with schools, ask what their evacuation plan is—a route to higher ground or vertical evacuation as seen here.
  5. Have a communication strategy: develop a way to communicate with your family to ensure they are safe should you be separated. Choose a meeting spot on high ground and practice getting to that spot in various conditions.
  6. Preparedness packs: put together emergency bags for your family and pets to take when you evacuate. It is recommended to stock the bag with 2-weeks worth of supplies.
  7. Prepare all locations: place a preparedness pack in your car, at work, at school, on your boat, and in your house to ensure you are ready no matter where you are.
  8. Maritime preparedness: if you are on a boat out in the water, move to depths of 180ft. Wait until you are given the all clear from officials to come back to the harbor. If you are in the harbor, exit your boat and move to higher ground.
  9. Stay updated: purchase a battery operated radio to receive updates from NOAA weather radio station.
  10. Pass it on: share your knowledge with friends and refer them to these links for more detailed information.