Tsunamis (pronounced soo-ná-mees), also known as seismic sea waves (mistakenly called “tidal waves”), are a series of enormous waves created by an underwater disturbance such as an earthquake, landslide, volcanic eruption, or meteorite. A tsunami can move hundreds of miles per hour in the open ocean and smash into land with waves as high as 100 feet or more.
From the area where the tsunami originates, waves travel outward in all directions. Once the wave approaches the shore, it builds in height. The topography of the coastline and the ocean floor will influence the size of the wave. There may be more than one wave and the succeeding one may be larger than the one before. That is why a small tsunami at one beach can be a giant wave a few miles away.
All tsunamis are potentially dangerous, even though they may not damage every coastline they strike. A tsunami can strike anywhere along most of the U.S. coastline. The most destructive tsunamis have occurred along the coasts of California, Oregon, Washington, Alaska, and Hawaii.
Earthquake-induced movement of the ocean floor most often generates tsunamis. If a major earthquake or landslide occurs close to shore, the first wave in a series could reach the beach in a few minutes, even before a warning is issued. Areas are at greater risk if they are less than 25 feet above sea level and within a mile of the shoreline. Drowning is the most common cause of death associated with a tsunami. Tsunami waves and the receding water are very destructive to structures in the run-up zone. Other hazards include flooding, contamination of drinking water, and fires from gas lines or ruptured tanks.
How can I protect myself?
- Tsunami Watch, Advisory or Warning
- What to do before and during a tsunami
- What to do after a tsunami
- Frequently asked questions about tsunamis
- National Weather Service Forecast Office
- National Tsunami Hazard Mitigation Program
- Tsunami Ready
- NWS Tsunami Brochure
- California Geological Survey
- Tsunami Brochure for Recreational Boaters
TSUNAMI WATCH, ADVISORY OR WARNING
Tsunami Watch: A Tsunami Watch is issued to alert emergency management officials and the public of an event that my later impact the watch area. The watch area may be upgraded to a warning or advisory – or canceled – based on updated information and analysis. Therefore emergency management officials and the public should prepare to take action. Watches are normally issued based on seismic information without confirmation that a destructive tsunami is underway.
Tsunami Advisory: A Tsunami Advisory is issued due to the threat of a potential tsunami, which may produce strong currents or waves dangerous to those in or near the water. Coastal regions historically prone to damage due to strong currents induced by tsunamis are at the greatest risk. The threat may continue for several hours after the arrival of the initial wave, but significant widespread inundation is not expected for areas under an advisory. Appropriate actions to be taken by local officials my include closing beaches, evacuating harbors and marinas, and repositioning of ships to deeps waters when there is time to safely do so.
Tsunami Warning: A Tsunami Warning is issued when a potential tsunami with significant widespread inundation is imminent or expected. Warnings alert the public that widespread, dangerous coastal flooding accompanied by powerful currents is possible and may continue for several hours after arrival of the initial wave. Warnings also alert emergency management officials to take action for the entire tsunami hazard zone. Appropriate actions to be taken by local officials may include the evacuation of low-lying coastals areas and repositioning of ships to deep waters when there is time to safely do so. Warnings may be updated, adjusted geographically, downgraded, or canceled. To provide the earliest possible alert, initial warnings are normally based on on seismic information.
WHAT TO DO BEFORE AND DURING A TSUNAMI
The following are guidelines for what you should do if a tsunami is likely in your area:
- Turn on your radio to learn if there is a tsunami warning if an earthquake occurs and you are in a coastal area.
- Move inland to higher ground immediately and stay there.
- Stay away from the beach. Never go down to the beach to watch a tsunami come in. If you can see the wave you are too close to escape it.
- CAUTION – If there is noticeable recession in water away from the shoreline this is nature’s tsunami warning and it should be heeded. You should move away immediately.
WHAT TO DO AFTER A TSUNAMI
The following are guidelines for the period following a tsunami:
- Stay away from flooded and damaged areas until officials say it is safe to return.
- Stay away from debris in the water; it may pose a safety hazard to boats and people.
- Save yourself – not your possessions
FREQUENTLY ASKED QUESTIONS
Are there any indicators that a tsunami may be coming?
Strong ground shaking, a loud ocean roar, or the water receding unusually far exposing the sea floor are all nature’s warnings that a tsunami may be coming. If you observe any of these warning signs, immediately go to higher ground or inland. A tsunami may arrive within minutes and may last for several hours. Stay away from coastal areas until officials announce that it is safe to return.
You may also hear that a Tsunami Warning has been issued. A Tsunami Warning might come via radio, television, telephone, text message, door-to-door contact by emergency responders, NOAA weather radios, emergency telephonic notification systems (such as Reverse 911 or Code Red) or in some cases by outdoor sirens. Move away from the beach and seek more information on local radio or television stations. Follow the directions of emergency personnel who may request that you evacuate beaches and low-lying coastal areas. Use your phone only for life-threatening emergencies.
Has California ever experience a tsunami?
Yes. Here are some of the notable tsunamis that have struck California:
1700 – Supported by written records of a tsunami hitting Japan and geological evidence in California, a magnitude 9 earthquake along the Cascadia Subduction Zone likely caused a 50-foot tsunami along California’s north coast.
1812 – A local earthquake triggered a tsunami near Santa Barbara. Frightened people in coastal villages retreated up the hill closer to the mission.
1946 – A tsunami generated in the Aleutian Islands caused tsunami flooding in parts of California, including a surge in Half Moon Bay that flooded over 1,000-feet inland.
1964 – A magnitude 9.2 earthquake in Alaska caused a tsunami 20-feet high that flooded 20 city blocks in Crescent City and killed 12 people statewide.
2006 – Strong water currents generated by a tsunami originating from the Kuril Islands caused $20-million worth of damage in Crescent City’s small boat harbor.
Do tsunamis pose a risk to Ventura County residents or visitors?
Yes. Tsunamis are a potential risk to residents and visitors along the Ventura County coast. Since 1812, there have been at least 9 recorded tsunamis that have caused local damage.
12/21/1812 – A 7.1 magnitude earthquake centered in the Santa Barbara or Ventura area caused a 6.5 foot run-up and damage to San Miguelito Chapel.
4/1/1946 – An 8.8 magnitude earthquake along the Aleutian Islands caused sand to sweep over the railroad tracks near Ormond Beach and minor ship berthing problems in Port Hueneme.
11/4/1952 – An 8.2 magnitude earthquake in Kamchatka caused a 2.3 foot run-up in Port Hueneme.
3/9/1957 – An 8.3 magnitude earthqake along the Aleutian Islands caused an approximate 2 foot run-up six hours after the first wave hit in Port Hueneme.
5/24/1960 – A 9.5 magnitude earthquake in Chile created a 4.4 foot run-up in Port Hueneme causing damage to docks and ships.
3/28/1964 – A 9.2 magnitude earthquake in Alaska caused the tide in Ventura to drop eight feet and large swells were reported in Oxnard.
9/29/2009 – A 8.2 magnitude earthquake in Samoa moved buoys within Ventura Harbor.
2/27/2010 – A 8.8 magnitude earthquake in Chile caused a 3 foot run-up in Ventura, as well as damage to 21 docks in Ventura Harbor.
3/11/2011 – A 7.1 magnitude earthquake in Japan caused a run-up within Venutra Harbor.
Will the Channel Islands protect us from a tsunami?
From the area where the tsunami originates, waves travel outward in all directions. Once the wave approaches the shore, it builds in height. The topography of the coastline and the ocean floor will influence the size of the wave. A small tsunami at one beach can be a giant wave a few miles away. Since we do not know where a tsunami might originate, we cannot presume to be safe from a tsunami simply because we have offshore islands.