If you’ve been to beaches and coastal communities in the Pacific Northwest, you’ve probably seen signs like these.
These signs tell you that you are in a place that is especially at risk for tsunamis.
Tsunamis have hit Washington in the past, and they will happen again in the future. Read more below to learn about how and where tsunamis occur, how to recognize a tsunami and evacuate, and what geologists at the Division of Geology and Earth Resources are doing to learn more about them.
This map shows areas where inundation modelling has been completed in Washington. The entire coastline of Washington may be at risk for tsunamis. Landslide-caused tsunamis can happen anywhere there are landslide hazards and lakes, rivers, or ocean. Clicking on the map will take you to the Geologic Hazards Map Page where you can find tsunami-related maps and brochures.
WHAT WE DO
The mission of the Washington Division of Geology and Earth Resources is to collect, develop, use, distribute, and preserve geologic information to promote the safety, health, and welfare of the citizens, protect the environment, and support the economy of Washington.
Develop and publish inundation maps
The Division works with NOAA to model the inundation of coastal areas from tsunamis. This is an important step for learning what areas will be affected by tsunami waves. The models use the shape of the ocean floor, topography of the land, and the expected size and shape of tsunami waves. The result is a series of maps that show the depth of water and the speed of the currents.
|Click here to find the published reports and inundation maps||Click here to find all of the inundation data in an online viewer|
Develop and publish evacuation maps
The Division works with the Washington Emergency Management Division and local, county, tribal, and other planners and emergency managers to develop, publish, and disseminate evacuation maps. These maps are made for areas that are especially at risk for damaging tsunamis.
|Click here to find the published brochures for specific areas||Click here to find all of the evacutation routes and meeting places in a searchable online viewer|
Help communities prepare
The Division helps communities to prepare for tsunamis by identifying hazard areas (tsunami inundation maps) and areas prone to earthquake-caused ground failure. This information helps planners to select the best evacuation routes and assembly areas. We publish the hazard maps and evacuation maps as PDFs and on our Geologic Information Portal. The portal includes an address locator to help people orient themselves and plan their best evacuation options.
We also work with communities to facilitate the planning and design of tsunami evacuation structures. The first vertical tsunami evacuation structure is currently being built as part of a new elementary school in the Ocasta School District at Westport. The evacuation structure is designed to hold 1,000 people above the gymnasium in an area that has little high ground for other types of evacuation.
Ocasta School elementary students helping to break ground on the new evacuation structure.
Work to increase public understanding
The Division works with the Emergency Management Division and local emergency managers to hold tsunami workshops in at-risk communities. The goal of these workshops is to help people understand their risks and make appropriate preparations.
In addition to workshops, we work to increase public understanding through media outlets such as this website, our blog Washington State Geology News, and the DNR blog Ear to the Ground. We post all of our new publications on the Washington State Geology News, so consider subscribing to stay up to date with the most recent geological research in Washington.
WARNING SIGNS AND EVACUATION
- When should I evacuate?
- Where and how do I evacuate?
Warning signs of a tsunami
For people in Washington, the single biggest warning of a potential tsunami is a large earthquake.
If you are near the ocean when there is a large earthquake or there is a tsunami warning,
EVACUATE TO HIGHER GROUND!
A tsunami may be about to hit if you:
- Hear a tsunami warning siren or receive a tsunami alert.
- Feel a strong earthquake near the ocean or a large lake. A strong earthquake is one that knocks people down, damages buildings, or lasts for longer than 20 seconds.
- Notice a very large approaching wave.
- See the water at the ocean disappear. As the tsunami approaches, sometimes sea level will rapidly drop as the wave gets taller.
- Notice an unusual rapid rise in sea level. Some tsunamis will have a surge in front of them as they approach land. These surges can be very damaging and dangerous.
- Notice a landslide that falls or slides into the ocean, a large lake, or a river.
EVACUATE IMMEDIATELY! if you notice any of these signs or hear a tsunami warning.
Tsunami waves can be 30–100 feet tall or more. If you cannot evacuate to higher ground, go as far inland as possible.
If there is a large earthquake, roads and bridges may be damaged. It may be impossible to evacuate by car.
KNOW HOW TO EVACUATE ON FOOT, even if that means walking along the road of the evacuation route.
Learn about your tsunami hazard and where you should go during an evacuation:
- If you live or work near the ocean or Puget Sound
- Before you travel near the ocean
- If you know someone who lives or works near the ocean or Puget Sound
Tsunami evacuation brochures and maps for parts of Washington are produced by the Washington Division of Geology and Earth Resources in concert with local and regional government offices.
This map shows all available tsunami evacuation brochures for Washington. Clicking on a region will download the brochure. Use your scroll wheel or the zoom buttons in the upper left corner to zoom.
The Geologic Information Portal has a Tsunami Evacuation theme that allows you to search for addresses and locations of interest. The information on the portal and in the brochures is the same.
WHO IS AT RISK?
Anyone in Washington who lives near the ocean or a large body of water is at risk of a tsunami or seiche.
There are four main types of tsunami risk in Washington. Each type of risk affects different parts of the state. Emergency planners and hazard geologists are working hard to learn more about these risks. Maps of tsunami inundation and evacuation brochures are produced by the Division of Geology and Earth Resources.
|Types of tsunamis and who they affect|
|Type of tsunami||Description||Damaging earthquake in Washington?||Area of largest tsunami||Time to evacuate|
|Remote||A tsunami is created by a distant earthquake or landslide and travels across the ocean||No||Pacific coastal communities||Hours|
|Cascadia subduction zone||Tsunami created by large M8–9 earthquake off the Washington, Oregon, or British Columbia coasts||Yes—significant damage||Pacific coastal communities||Tens of minutes|
|Local earthquake (for example, the Seattle or Tacoma faults)||Tsunami created in large body of water from an earthquake on local faults||Yes—significant damage is likely||Communities close to the body of water||Minutes to tens of minutes|
|Landslide-caused tsunami||Large landslide occurs underwater or slides from land into water||Usually, but not always||Depends on where the landslide occurs||Minutes to tens of minutes|
HOW TSUNAMIS HAPPEN
- What is a tsunami?
- Detection and warning
What is a tsunami?
Tsunamis are large and destructive ocean waves caused by earthquakes, landslides, or volcanic eruptions. When a large wave is caused by the resonance of wave energy it is called a 'seiche'. Although they are created differently, both seiches and tsunamis can be large and destructive.
Tsunamis from large earthquakes travel across entire oceans and can be 30–150 feet tall when they reach shore. They are caused when a large amount of water is moved very quickly, and are more like large walls of water than a single breaking wave.
Tsunami waves are different than normal ocean waves which are caused by the friction of wind on the ocean surface.
Tsunamis will hit Washington again, but it is impossible to predict exactly when. Know what to expect. Know how to evacuate.
What causes a tsunami?
Tsunamis are usually caused by either earthquakes, landslides, or volcanic eruptions. Sometimes a large earthquake can cause a tsunami and trigger a landslide that creates a second tsunami.
Earthquakes are the most common cause of tsunamis, and usually require a large (M7 or greater) earthquake.
Only those earthquakes that cause vertical movement of the ocean floor will create a tsunami. The rapid uplift of the ocean floor transfers an enormous amount of energy and creates a powerful wave. The tsunami wave can be hundreds of miles long and up to several meters tall when it is created.
The 1964 Alaska Earthquake triggered several tsunamis. The tsunami washed several boats into the heart of Kodiak, Alaska. Photo by U.S. Navy, March 30, 1964.
The following short video describes several ways that tsunamis are created by earthquakes.
The types of faults that produce tsunamis are most common along subduction zones. The Cascadia subduction zone off the coast of Oregon, Washington, and British Columbia is a good example of where tsunamis are created. Other tsunami-generating subduction zones occur in Alaska, Japan, Central America, South America, and along the eastern edge of the Indian Ocean.
The Cascadia subduction zone
The Cascadia subduction zone off the coast of Washington, British Columbia, and Oregon is the biggest tsunami hazard that we face. This very large fault is capable of making some of the largest and most damaging earthquakes in the world. These earthquakes also cause very large and damaging tsunamis. The following series of diagrams shows how tsunamis are created along the Cascadia subduction zone.
Other faults in Washington, such as the Seattle fault and Tacoma fault can also move the ocean floor and cause tsunamis.
Large underwater landslides also cause tsunamis. Sometimes, but not always, the slides themselves are triggered by an earthquake. The 1964 Alaska earthquake created a large tsunami and also triggered many landslides that made other tsunamis. In Valdez Inlet, one of these landslide-created tsunamis reached heights of 200+ feet (67 meters). Underwater landslides can occur at any time and in many places throughout the world.
To learn more about landslides, visit our landslides page.
Volcanic eruptions can cause also cause tsunamis. Volcanoes near the ocean or a large body of water can cause a tsunami during eruption as pyroclastic flows (a mixture of ash, rock, gas, and water) rapidly flow downhill into the water.
Volcanic eruptions often have lots of earthquakes, and these can also cause tsunamis, either by moving the ocean floor, or by causing landslides. If the eruption is so large that part of the volcano collapses, then this collapse can also cause a tsunami. Oregon State University maintains a list of noteworthy volcano-induced tsunamis.
Early stages of May 18, 1980 eruption of Mount St. Helens from ~20 miles away. Note helicopter in left third of image. Photo by Ralph W. Frank.
How big and how fast are tsunamis?
Tsunamis are especially destructive and dangerous because they travel quickly and can reach great heights. It is surprising to learn that most tsunamis are less than three feet tall when they are created. A tsunami in the open ocean can travel at the speed of a jet (500 mph) yet pass unnoticed beneath most ships.
Many people think that a tsunami will be very tall and breaking (like a surf wave). This may not be true. Although many tsunamis are 30–100 feet tall, they are still very broad when they hit the shore. Tsunamis are more like a giant wall of water.
This video shows the arrival of a tsunami in a coastal community of Japan after the 2011 Tohoku earthquake. The tsunami arrives over several minutes and flows straight over the land, flooding buildings up to their second story.
Parts of a wave
Simplified schematic showing the parts of an ocean wave. At the surface, there are crests and troughs. Crests are separated by a wavelength. The depth to which a wave's effects can be felt depends on the wavelength and wave height. From http://www.rsmas.miami.edu/blog/2012/10/22/what-happens-underwater-durin...
Speed of tsunamis
When tsunamis are created they have a very long wavelength. This means that the distance from wave top to wave top is large, sometimes hundreds of miles. These long wavelengths mean that the tsunami can travel very quickly without losing energy. A typical tsunami can travel at speeds of 500 mph while normal ocean waves travel at less than about 5 mph.
In 1946, a tsunami was created by an earthquake in the Aleutian Islands of Alaska. In less than 5 hours, the tsunami reached Hawaii with waves as high as 55 feet and killed 173 people.
This video shows the how the 1700 AD tsunami from the Pacific Northwest may have crossed the Pacific Ocean.
Height of tsunamis
As a tsunami approaches shallow water, it starts to slow down and build in height. This is because the ‘bottom’ of the tsunami starts to feel the ocean floor and is forced upward. This compression is called ‘shoaling’ and causes the wave to slow down and grow in height.
As the front of the wave slows down, more and more of the wave ‘catches up’ with the front. The result is a wave that was stretched out over 100 miles is now forced into a very small area near the shore.
This animation shows how waves get taller as they reach shallow water (shoaling). Tsunamis have very long wavelengths which means that the get much much taller as they shoal. Animation by Régis Lachaume at https://en.wikipedia.org/wiki/Wave_shoaling.
The final height of a tsunami when it hits the shore is a combination of the original tsunami and the shape of the nearby ocean floor. Some places are tsunami ‘funnels’ and create very large waves by focusing the tsunami energy. In other places, the ocean floor may actually lower the height of a tsunami and make it less powerful.
Tsunamis have many waves
Most tsunamis have many separate waves spaced out over tens of minutes to hours. The first wave may not be the highest. If there is a tsunami, expect others to follow.
The first wave to strike Crescent City, California, after the 1964 Alaska earthquake, was 9 feet above the tide level. The second wave arrived 29 minutes later and was 6 feet above tide. The third wave was about 11 feet above the tide level. The fourth and most damaging wave was more than 16 feet above the tide level. The third and fourth waves were the most damaging and killed 11 people.
Tsunami detection and warning
Once a tsunami has been created, there is usually a delay of several minutes to hours before it reaches land. For example, there will be about 15 minutes between an earthquake on the Cascadia subduction zone and when the first wave hits the Pacific shoreline. This same tsunami will take about 4–5 hours to reach Hawaii and 8–10 hours to reach Japan.
This time delay is important for evacuating people. Tsunami warning systems have been developed around the world to detect possible tsunamis and provide warnings for people. All warning systems consist of two parts, a detection network and a communication network.
The Pacific Tsunami Warning Center is the US site that monitors and issues warnings for land around the Pacific Ocean and Caribbean Sea.
Most detection networks for tsunamis use the seismic waves from the earthquake to predict if a tsunami will be created. Seismometers throughout the world are constantly recording earthquakes. When a large earthquake happens, computers rapidly determine what kind of earthquake it is and decide if it is likely to create a tsunami. Because many large earthquakes last for several minutes, this process can occur even while the earthquake is still happening. If the earthquake is predicted to create a tsunami, a warning is issued.
A network of tidal buoys throughout the oceans is used to track the tsunami. As more information is gathered, the warnings are updated.
This interactive graphic shows how seafloor seismometers and buoys detect tsunamis and relay signals. Click on "Trigger Mode" or "Request Mode" to see how the system works.
An important aspect of the warning system is communicating the warning to the people who are in danger. In the US this occurs through the Emergency Alert System. In some beach communities there are loud sirens that warn of a potential tsunami. You can subscribe to SMS, email, or phone notifications. Radio, television, and internet warning systems also exist.
Although substantial loss of life can occur with any major tsunami, people who are warned ahead of time are better prepared to survive.
For people in Washington, the single biggest warning of a potential tsunami is a large earthquake.
Tsunamis are likely if there is a large earthquake that moves the floor of the ocean, or there is a landslide into a large body of water. We know that large earthquakes have happened in the past, and will happen again in the future. We cannot predict exactly when these events will happen, but we are getting better at predicting the size of the tsunami that is created.
The Washington Division of Geology and Earth Resources works with a division of NOAA to model the inundation of coastal areas from tsunamis. This is an important step for learning what areas will be affected by tsunami waves. The models use the shape of the ocean floor, topography of the land, and the expected size and shape of tsunami waves. The result is a series of maps that show the depth of water and the speed of the currents.
Click here to find the published reports and inundation maps Click here to find all of the inundation data in an online viewer
NOAA has developed an interactive map that shows the travel times across the Pacific Ocean for different tsunamis.
The Center for Tsunami Research has a series of animations from real tsunamis that show how the waves moved. Geologists at the Division and at NOAA use this kind of data to improve our ability to predict how tsunamis move along coasts and across oceans.
SOME HISTORIC TSUNAMIS
The list below shows a few of the major tsunamis that have happened in recorded history. Wikipedia hosts a list of historic tsunamis that contains many more events and much more information.
|Some Historic Tsunamis|
|Name||Date||Original location||Maximum wave height||Type of tsunami||Size of earthquake|
|Tohoku||Mar. 11, 2011||Japan||130 feet||Subduction zone||M9.0|
|Notes: Nearly 20,000 people died and a major nuclear meltdown occurred. The Tohoku event is similar to what is expected for the Cascadia subduction zone off the coast of Washington.|
|Cascadia||Jan. 26, 1700||Washington–Oregon coast||~100 feet||Subduction zone||M8.7–9.2|
|Notes: The tsunami created during this event is recorded in the geologic record and in Native American oral history. The tsunami may be the inspiration for the battle of the Thunderbird and Whale. Japanese records precisely document the tsunami from this event because it also caused significant destruction along the coast of Japan.|
|Indian Ocean||Dec. 26, 2004||Sumatra,
|108 feet||Subduction zone||M9.2|
|Notes: One of the most devastating natural disasters in history with nearly 280,000 deaths and more than 1 million people displaced. A lack of a tsunami warning system in the Indian Ocean meant that people did not know to evacuate after the earthquake.|
|Spirit Lake||May 18, 1980||Spirit Lake, Washington||853 feet||Volcanic landslide||None|
|Notes: A large landslide from the Mount St. Helens eruption caused an enormous tsunami in Spirit Lake.|
|Good Friday Earthquake||Mar. 27, 1964||Alaska||100 feet||Subduction zone||M9.2|
|Notes: Third-strongest earthquake in recorded history—shaking lasted 3 minutes. Tsunami caused damage throughout the Pacific Ocean, including 110 deaths, some as far away as Crescent City, California. Also caused a large underwater landslide that created a 200-foot tsunami in Valdez Inlet.|
|Lituya Bay||Jul. 9, 1958||Lituya Bay, Alaska||1,720 feet||Earthquake-triggered landslide||M7.8|
|Notes: An earthquake on the Fairweather fault caused 39 million cubic yards of rock and ice (a cube of land ~1,000 feet on each side) to fall into the ocean. The resulting 'splash' destroyed everything on shore up to 1,720 feet above sea level and sent a huge tsunami into the bay. This is the largest tsunami in history.|
|Aleutian Islands Tsunami||Apr. 1, 1946||Alaska||130 feet||Subduction zone||M8.1|
|Notes: The tsunami from this earthquake caused 165 deaths and significant destruction in Alaska, Hawaii, and other states and countries bordering the Pacific Ocean. It resulted in the formation of the Pacific Tsunami Warning Center.|
|Krakatoa||Aug. 26–27, 1883||Sunda Strait, Indonesia||125 feet||Volcanic explosion, collapse of magma chamber under ocean floor||None|
|Notes: The explosion from the volcanic eruption is thought to be the loudest sound in modern history, reaching people over 3,000 miles away. The collapse of the spent magma chamber beneath the ocean floor caused a tsunami throughout the southern Pacific Ocean and killed at least 36,000 people. The ash from the eruption changed global weather patterns for several years.|
|All Saints Day||Nov. 1, 1755||Offshore of Lisbon, Portugal||50 feet||Earthquake of unknown type||M8.5–9.0|
|Notes: The earthquake and tsunami occurred during mass on All Saints Day and killed at least 40–50,000 people in Lisbon alone. The ocean receded as the tsunami approached, and many people ran to the beach to escape the earthquake’s destruction, only to be faced with a tsunami. This event appears to be the first scientifically studied earthquake and is credited as founding the modern field of seismology.|