Tsunamis in Oregon
|In Harm's Way|
|Recent scientific studies investigating buried coastal sand deposits at sites stretching from Northern California to British Columbia, Canada, have lead researchers to the conclusion that major earthquakes capable of generating tsunamis impact our area about every 300 to 600 years. These layers of buried sand were carried inland by the advancing tsunami waves and left as evidence of this infrequent yet devastating natural hazard. Unlike tsunamis generated in distant locations, the nearby earthquake that generates a local tsunami may be the only warning coastal residents receive before the tsunami waves flood low lying locations within minutes after the earthquake occurs. |
Oregon has also been hit by tsunamis caused by earthquakes occurring in other areas of the Pacific Ocean's "ring of fire." The March 1964 Alaska earthquake generated a tsunami that caused many casualties and extensive damage in Alaska then traveled the great distance to the US West Coast and Hawaii causing additional fatalities and damage. In Oregon, four campers on the beach were crushed by logs carried by the unexpected high water of the advancing tsunami. For tsunamis generated by earthquakes in distant locations, the Pacific Tsunami Warning System provides advance warning for people in coastal communities to evacuate to higher ground.
More and more people are moving to the Oregon coast to live, work and enjoy a myriad of recreational opportunities. It is important to recognize the prehistoric evidence of major local tsunamis as well as the accounts of damaging historic tsunamis as an opportunity to learn about this natural hazard and ways to protect yourself, your family and friends. What you learn from this information could save your life!
|Soo-nam-ee (harbor wave)|
|A tsunami has been called a tidal wave but has nothing to do with the tide. Rather, it is an unusual increase (sometimes preceded by a decrease before the first wave arrives) in sea level that floods low-lying areas and causes unusual currents in harbors and bays. Tsunamis are most always caused by earthquakes occurring near to or underneath the ocean. The earthquakes are the result of sudden movements in the earth´s crust that effectively transmit energy to the ocean causing a tsunami. Not all oceanic earthquakes generate tsunamis. |
A tsunami is not a single wave but a series of long period waves that can cause havoc along the coastline, in harbors and bays, and move up coastal rivers. The unusual, wild oscillations of sea level caused by the tsunami can last for hours following arrival of the first wave. In 1964, many people in Crescent City, California, thought it was safe to return to the harbor area only to be killed by later arriving tsunami waves. The same happened in Hilo, Hawaii, in 1960. In both of these instances, people received ample warning of the arriving tsunami but did not heed the instructions of local emergency management authorities.
|People located in low-lying areas near the ocean are at greatest risk from tsunami flooding. The tsunami can flood (inundate) inland areas, well beyond the range of normal high water. For this reason, scientists are developing numerical simulations of tsunami that will help define areas where it will be safe to evacuate in advance of the tsunami's arrival. |
Boats and ships in harbor are also at great risk from the wild changes in sea level. The water level can change so fast that lines holding ships to the pier will break like string. Navigating in these conditions will be treacherous as unpredictable, dangerous currents can continue for hours while the water in the harbor shifts back and forth.
- The earthquakes that cause tsunamis in Oregon can occur nearby or in distant areas like Alaska or Russia.
- A severe earthquake associated with the Cascadia Subduction Zone off the Oregon coast would generate a destructive tsunami impacting coastal communities within minutes. A locally generated tsunami has the potential to cause damage that far exceeds the damage inflicted by a tsunami of distant origin.
- Tsunamis generated in distant locations of the Pacific Basin can take four hours or longer to reach Oregon's coastline.
- In the deepest ocean waters a tsunami is unrecognizable and can travel over 500 miles per hour, about the speed of a commercial jet.
- As the tsunami approaches the coastline, and shallower water, its speed slows and wave height increases dramatically. But, the tsunami still moves faster than a person can run once it reaches the shoreline.
- Sometimes, but not always, the tsunami's arrival is preceded by a noticeable withdrawal of the water.
- The configuration of the near-shore ocean bottom and coastline play mean tricks with the tsunami waves. They can cause the waves to amplify in one area and be weakened in another nearby area. Tsunamis are unpredictable as they come ashore and flood low-lying areas.
- Harbors, bays and river mouths are very sensitive to tsunamis. Unpredictable currents, terrifying waves, and water level oscillations that can last for hours will play havoc with ships, boats, and dock facilities.
- The rapidly increasing sea level caused by the tsunami picks up debris, rocks, logs and other materials that act as projectiles that further destroy buildings and cause casualties.
- As the water level rises due to the tsunami, wind waves and ocean swells will continue to 'ride on top' of the tsunami and potentially add to the destructive force of the tsunami.
- Sand layers deposited by a prehistoric tsunami that occurred around the year 1700 caused destructive, flooding waves that impacted much of the Oregon coastline. This tsunami was preceded by a severe earthquake, magnitude 8 or possibly greater, that caused land along the coast to sink before it was inundated by the tsunami waves. Historic records from Japan tie the arrival of unusual waves along the Japan coastline to this earthquake and tsunami generated off the Oregon coast!
- March 28, 1964. A tsunami hit the Oregon coastline about four hours after it was generated by a severe earthquake in Prince William Sound, Alaska. Four people in Oregon were killed by this tsunami. Destruction occurred at numerous locations, including Seaside, Cannon Beach, Depoe Bay, Florence, Rogue River, along the Umpqua River, Waldport and in Newport Bay.
|Stay Safe, What to Do |
|For tsunamis generated by earthquakes in or near to Oregon, there will be very little time for the coastal population to take action. |
- Tsunami waves could arrive along the coastline in as little as five minutes, flooding low-lying areas, traveling up rivers that empty into the ocean, and causing wild water level fluctuations in harbors and bays.
- The strong ground shaking of the earthquake will be a natural warning to move to higher ground, quickly.
- Once the earth stops shaking, there will be no time to gather personal belongings.
- You, your family, and friends must not waste any time and evacuate to high ground above the area of tsunami inundation.
- Although there may be an official warning of the tsunami issued, local failures in phone systems, electricity, and TV/radio may preclude hearing the warning.
- County and local emergency management authorities have developed specific evacuation procedures for Oregon coastal areas. Understand the tsunami evacuation plans before disaster strikes.
For tsunamis generated in distant locations, like Alaska or Russia, you will receive advance warning of the tsunami's arrival from your local emergency management office and on TV/radio. Follow the instructions they provide. You will most likely be asked to evacuate to higher ground. Remember, you will not feel the earthquake that generates tsunamis from distant areas of the Pacific.
If you are in a boat in harbor and there is sufficient time, you may be asked to move your craft to deep water, avoiding the impact of the tsunami in the harbor. For a local tsunami event, where you can feel the earthquake, you may find the safest course of action is to leave your boat at the pier and physically move yourself, family and friends to higher ground above the inundation zone.
Since a tsunami is a series of waves, the damaging effects can last for hours following the arrival of the initial wave. DO NOT return to low lying areas susceptible to tsunami flooding until you have received the all clear from local authorities.
Heed this safety information on tsunami preparedness but do not let it deter you from enjoying the Oregon coast. Tsunamis do not happen very often, but by planning ahead you will know how to respond if you feel a strong local earthquake or hear that a tsunami warning has been issued by the authorities.
|Want to Know More ?|
- Contact your local emergency management office if you would like to know more about tsunamis and tsunami preparedness activities for your area.
- The Oregon Department of Geology and Mineral Industries (DOGAMI) in Portland has a wealth of recent scientific reports (on the buried sand deposits) and historical information on tsunamis and earthquakes in Oregon. They have developed tsunami inundation maps for the Oregon coastline.
- Your local library will have information on natural hazard disaster planning so you can prepare for these events beforehand. Local chapters of the Red Cross are an excellent source of information on disaster planning, too.
- Take preventive action now, before you hear or see that a tsunami is coming!
- In Salem, contact the Oregon Emergency Management Office at P. O. Box 14370, Salem OR, 97309 or contact Althea Rizzo, Geologic Hazards Program Coordinator.
|Additional Tsunami Info Sites|
General tsunami information can be found on the U. Of Washington
web site and preparedness and mitigation information on what to do before, during and after the tsunami can be found in the FEMA-Tsunami Facts