Tsunamis:

On March 28, 1964 Crescent City was damaged by a tsunami originating from the Great Alaskan subduction zone earthquake. Note how whole buildings were lifted and moved by the force of the water. An aerial view looking north. Del Norte County Historical Society Photograph.

Tsunami (soo-NAH-mee) Facts:

Tsunami is a series of sea waves most commonly caused by earthquakes beneath the sea floor. In the open ocean, tsunami waves travel at speeds of up to 600 miles per hour. As the waves enter shallow water, they may rise to several feet or, in rare cases, tens of feet, and can cause great loss of life and property damage where they come ashore. The first wave is often not the largest; successive waves may be spaced tens of minutes apart and continue arriving for a number of hours. There are two kinds of tsunamis which could affect the North Coast:

1. Locally generated tsunamis: If a large earthquake displaces the sea floor near our coast, the first waves may reach the coast within minutes after the ground shaking stops. There is no time for authorities to issue a warning. People on the beach or in low coastal areas need to be aware of the tsunami risk and be prepared to move to higher ground as soon as they are able after a strong earthquake and stay there until told by an official source that the danger has passed.

2. Distant-source tsunamis: Tsunamis may also be generated by very large earthquakes in other areas of the Pacific Ocean and may reach our coastline many hours after the earthquake occurred. Tsunami Warning Centers are responsible for gathering information on earthquakes which may generate tsunamis and alerting local officials who may order evacuation. If you are in an isolated area, however, you may not hear the official announcements. If you notice a sudden drop or rise in sea level, nature may be warning you of impending danger and you should move inland or to high ground immediately.

March 28, 1964 Crescent City. Looking east from Second and F Streets. Del Norte County Historical Society Photograph.

What Can I Do Ahead of Time to Protect Myself and My Family From a Tsunami?

• Make disaster plans beforehand. Talk to the people you live with about what may happen during a strong earthquake or other disaster. If you live or work in a low-lying coastal area, know where to go to survive a tsunami. Hold earthquake/tsunami drills at home or at work.

• Assemble a portable disaster supply kit. Have a kit available in your car, at home and at work. Your kit should include a portable radio with fresh batteries, water, first aid supplies, flashlight, and extra clothes or a blanket. Put your kit in a backpack and leave it in an easy-to-reach place.

• Contact local emergency officials. Find out what areas are most vulnerable to tsunami hazards, which areas are safe, and which routes are best for evacuation.

• Take a first aid class. Learn survival skills, talk with your family, friends and neighbors. Knowledge is your greatest defense against any potential disaster.

THE APRIL 25, 1992 TSUNAMI

The Cape Mendocino earthquake produced a tsunami that reached tide gauges at the mouth of Humboldt Bay about 20 minutes after the shaking with wave heights of about one foot. It reached communities closer to the Cape in even less time. The tsunami arrived at Crescent City in 50 minutes and was detected in Oregon, the San Francisco Bay Area, Santa Barbara, and Hawaii.

Although not destructive, the April tsunami is important because it illustrates both how quickly a wave can arrive at nearby coastal communities and how long the danger period can last. The first wave reached Crescent City in less than an hour, but the highest waves, about one-and-a-half-feet, arrived nearly four hours later. Abnormal sea levels continued for more than eight hours.

IF YOU FEEL A STRONG EARTHQUAKE WHICH LASTS A LONG TIME WHEN YOU ARE ON THE COAST:

1. Protect yourself during the earthquake. Duck, cover and hold if inside and watch for falling objects if outside until the earthquake is over.

2. Move to higher ground immediately. Gather your family members and evacuate quickly. Leave everything else behind. A tsunami may be coming within minutes. Go on foot if at all possible. If there is no high ground, move inland away from the coastline.

   DO NOT WAIT FOR AN OFFICIAL WARNING

3. Stay away from the coast. A later wave may be higher than the first! Damaging waves may continue to arrive even hours later.

4. Listen to your radio. Wait until an official all clear signal has been given before returning to low-lying areas.

• Never go to the coast to watch for a tsunami if you hear that a warning has been issued. Tsunamis move faster than a person can run. Also, incoming traffic hampers safe and timely evacuation of coastal areas.

• Tsunamis are not surfable! They are not V-shaped or curling waves. Most frequently they come onshore as a rapidly-rising turbulent surge of water choked with debris.

• All tsunamis - like hurricanes - are potentially dangerous, even though they may not damage every coastline they strike.

• An earthquake in your area is a natural tsunami warning. Do not stay in low-lying coastal areas after a strong earthquake has been felt.

• Damaging tsunamis are very rare. Our coastlines are vulnerable but tsunamis are infrequent. Understand the hazard and learn how to protect yourself, but donØt let the threat of tsunamis ruin your enjoyment of the beach.

Tsunami, Hawaii 1957. Magnitude 8.3 earthquake in the Aleutian Islands 2,100 miles away caused $5 million damages in Hawaii. Photos by Henry Helbush.

What is a low-lying area and how high is high ground?

The earthquake planning scenario, includes a study of tsunami wave heights in the Humboldt Bay and Crescent City areas. Areas below the ¹blue lineœ should be considered at risk from a tsunami and persons living or working in these areas should know how to evacuate and where to go if a strong earthquake occurs. Most of the coastline, however, has not been studied and it is difficult to predict how high the waves are likely to reach. Other potentially hazardous areas are coastal river banks. Typical peak wave heights from large tsunamis in the Pacific Ocean over the last eighty years have been between 21 and 45 feet at the shoreline. A few waves, however, have locally been higher - as much as 100 feet in a few isolated locations. The best general advice available today is to:

• Go to an area 100 feet above sea level, if possible, or go up to 2 miles inland, away from the coastline. If you can not get this high or far, go as high as you can. Every foot inland or upwards may make a difference.

• Go on foot if at all possible because of traffic, damage to roads, downed power lines and other earthquake debris.

How do I know when to evacuate?

Evacuation after a strong earthquake can be hazardous. In the process of hurrying to high ground, you may expose yourselves to other earthquake hazards such as dangerous debris and falling objects dislodged by aftershocks. Coastal Humboldt County has experienced frequent strong earthquakes in historic times. None of these earthquakes have produced damaging tsunamis. The 1992 Cape Mendocino earthquake produced about 12 seconds of strong shaking; the 1994 Eureka earthquake was over in only a few seconds. A major Cascadia subduction zone earthquake will shake the ground strongly for 20 seconds or longer. Get into the habit of counting how long the earthquake shaking lasts. If you count 20 seconds of very strong ground shaking, evacuate as soon as it is safe to do so.

To learn more about tsunamis click here

Do You Wish To Continue?

Do You Wish to Return to Beginning?