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Frequently Asked Questions

The last major Pacific wide tsunami occurred in 1964. The rare occurrence of a Pacific wide tsunami in recent times makes them increasingly important to understand as more and more people live and play in coastal areas. Currently, many people are not aware of the actual threat tsunamis pose to many coastal areas throughout the Pacific. This section has been designed to answer many of the common questions concerning the nature of tsunamis; their occurrence here in Hawaii and the Pacific region; and what scientists and civil authorities have done to improve our understanding and prevent loss of life from this destructive natural phenomenon.
Please read on and discover the fascinating facts about Tsunamis! If you have trouble with any of the terms, look them up in the Tsunami Glossary.

Be sure to check out our
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black ball Where is Hilo, Hawaii?
black ball What does the word tsunami mean?
black ball Is there a Hawaiian word for tsunami?
black ball What causes a tsunami?
black ball Could Nuclear testing create a tsunami?
black ball How is a tsunami wave different from a normal wave?
black ball How does a tsunami behave as it approaches land?
black ball How long does it take a tsunami to reach land?
black ball How many waves are there in a tsunami?
black ball What is run-up and inundation?
black ball How are tsunami wave heights measured?
black ball What is the "wrap-around" effect?
black ball Do all oceans have tsunamis?
black ball What is the Tsunami Warning system?
black ball What is the difference between a Tsunami Watch and a Tsunami Warning?
black ball How many warnings have been issued by the Pacific Tsunami Warning Center since it was established?
black ball What should I do or not do in a tsunami warning?
black ball If I need to evacuate, what should I bring with me?
black ball Can the arrival time of a tsunami be accurately predicted?
black ball What has been the most destructive tsunami to strike the Hawaiian Islands in recent history?
black ball How many Pacific-wide tsunamis have struck the Hawaiian Islands in recent history?
black ball How many locally generated tsunamis have occurred in the Hawaiian Islands in recent history?
black ball How are inundation/evacuation areas determined?
black ball Since I don ′t live in an inundation area why should I be concerned?
black ball I own a boat: what should I do when there is a tsunami warning?
black ball If I would like more information on tsunamis who should I contact?

Where is Hilo Hawai ′i?
Hilo, pronounced (hee-low), is located on the windward (eastern) coast of the island of Hawaii, 200 miles southeast by air from Honolulu, the state capitol. Nestled between the flanks of the volcanic peaks Mauna Kea and Mauna Loa, Hilo, and its 49,000 residents surround Hilo Bay, the second largest deep water port in the island chain. To island residents, Hilo is most famous for its rainfall (about 120 inches per year), hence agriculture is the dominant industry in the surrounding area. hilo
The geographic isolation of the Hawaiian Islands has resulted in unique assemblages of plants and animals found nowhere else on Earth. Surrounded by Pacific Ocean, the history of the Islands has been shaped by the interactions between land and sea. Hilo occupies a unique spot in this history, having been frequently subjected to devastating tsunami waves. In terms of property damage and loss of human life from tsunamis, Hilo surpasses all other areas in Hawaii, and consequently has the reputation as the tsunami capital of the United States.
Hilo is largely affected by tsunamis for many reasons, one of which is the local topography and bathymetry.  The orientation of the Hawaiian Ridge and coastline, with respect to the direction and approach of a tsunami, plays an important role.  Also, small funnel-shaped bays, like Hilo Bay, harness the tsunami wave energy and amplify the heights of the waves.  That leads to greater destruction.
What does the word tsunami mean?
"Tsunami" is a Japanese word which translates as "harbor wave", now used internationally to refer to a series of waves traveling across the ocean with extremely long wavelengths (up to hundreds of miles between wave crests in the deep ocean).  When these waves approach shore, the speed of the wave decreases as they begin to "feel" the bottom.  It is at this time that the height of the wave drastically increases.  As the waves strike shore they may inundate low-lying coastal areas resulting in mass destruction and in many instances loss of life.   Often a tsunami is incorrectly referred to as a tidal wave.  Tidal waves are simply the periodic movement of water associated with the rise and fall of the tides produced by the gravitational attraction of the sun and moon. Tsunamis have no connection with the weather nor with tides.
Is there a Hawaiian word for tsunami?
There are two words used to describe tsunamis. "Kai e ′e" is a general word for tsunami waves, and "Kai mimiki" is used to describe the withdraw of the water before the Kai e ′e arrives.  The withdraw of the water is actually the trough of the tsunami reaching shore.
What causes a tsunami?
Oceanographers often refer to tsunamis as seismic sea waves as they are usually the result of a sudden rise or fall of a section of the earth ′s crust under or near the ocean.  A seismic disturbance can displace the water column, creating a rise or fall in the level of the ocean above. This rise or fall in sea level is the initial formation of a tsunami wave.
Tsunami waves can also be created by volcanic activity and landslides occurring above or below the sea surface.  These types of activity produce tsunamis with much less energy than those produced by submarine faulting.  The size and energy of these tsunamis dissipates rapidly with increasing distance from the source, thus resulting in more local devastation.
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Could Nuclear testing create a tsunami?
Nuclear testing at and near Pacific islands, with ample wave detection equipment included, showed that such explosions do not propagate hazardous tsunami waves.
How is a tsunami wave different from a normal wave?
The waves you see at the beach are generated by wind blowing over the sea surface.  The size of these waves depends on the strength of the wind creating them and the distance over which it blows.  Generally the distance between these waves, known as the wavelength, ranges from a couple of feet to perhaps a thousand feet.   The speed of these waves as they travel across the ocean ranges from a few miles an hour up to sixty miles an hour in some instances.
Tsunami waves resulting from physical mechanisms (see above question) behave much differently than wind generated waves.  The magnitude of the disturbance causing the tsunami is the primary factor influencing the size and strength of the waves.   The height of the wave when it is generated is very small, usually less than a few feet.  The distance between successive wave crests or the wavelength however, is much larger than that of a normal wave and may be hundreds of miles apart.  Depending on the depth of the water in which the tsunami is traveling, it may attain speeds of up to 500 miles an hour.
How does a tsunami behave as it approaches land?
When the waves of a tsunami approach land, their appearance and behavior become dependent on several local factors. Two of the most important factors are the topography of the seafloor (bathymetry) and the actual shape of the shoreline. As a tsunami encounters shallow waters surrounding the shoreline, its height can increase from a meter (three feet) or less to over 15 meters (50 ft.). Wave heights can also be increased when concentrated on headlands or when traveling into bays having wide entrances that become progressively more narrow. The presence of an offshore coral reef can dissipate the energy of a tsunami, decreasing the impact on the shoreline. Normal wind swell may ride atop of a tsunami wave thereby increasing wave height.
The image most people have of a tsunami is a large, steep wave breaking on the shore. This image is seldom the case. Most tsunamis appear as an advancing tide without having a developed wave face, resulting in rapid flooding of low-lying coastal areas. Sometimes, a bore can form during which an abrupt front of whitewater will rapidly advance inland much similar to the tidal bore formed at the mouth of large rivers.
Another event that may result from a tsunami is a standing wave or seiche. A seiche occurs in bodies of water that are partially or completely enclosed, such as Hilo Bay, creating a standing wave that continually sloshes back and forth. The appearance of a seiche would be very similar to what happens when you place a glass of water on the table; the water rocks back and forth before settling. When a seiche is generated by a tsunami, subsequent tsunami waves may arrive in unison with a seiche resulting in an increase in the drawdown in sea level and a dramatic increase in wave height. Seiche waves may continue several days after a tsunami.
How long does it take a tsunami to reach land?
Once generated, a tsunami wave in the open ocean can travel with speeds greater than 500 miles an hour.  These waves can travel across the Pacific Ocean in less than one day.  Locally generated tsunamis can reach coastlines in just minutes.
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How many waves are there in a tsunami?
A tsunami generally consists of a series of waves, often referred to as the tsunami wave train.  The amount of time between successive waves, known as the wave period, is usually a few minutes; in some instances, waves are over an hour apart.  Many people have lost their lives after returning home in between the waves of a tsunami, thinking that the waves had stopped coming.
What is run-up and inundation?
When a tsunami approaches a coastline, the wave begins to slow down and increase in height, depending on the topography of the sea floor.  Often the first signs of a tsunami are a receding water level caused by the trough of the wave.  In some instances though, a small rise in the water level just before the recession, has been observed.  Regardless, the incoming wave approaches much like the incoming tide though on a much faster scale.  The maximum vertical height to which the water is observed with reference to sea level is referred to as run-up.  The maximum horizontal distance that is reached by a tsunami is referred to as inundation.
How are tsunami wave heights measured?
The wave height of a tsunami can be highly variable in a local area depending on the underwater topography, orientation to the oncoming wave, the tidal level, and the magnitude of the tsunami.  Because direct physical measurement of a tsunami wave would be a life threatening event, a common method for determining tsunami wave height is by measuring the runup, the highest vertical point reached by the wave.  Runup heights are measured by looking at the distance and extent of salt-killed vegetation, and the debris left once the wave has receded.  This distance is referenced to a datum level, usually being the mean sea level or mean lower low water level.  The reference to mean lower low water is more significant in areas with greater tidal ranges such as in Alaska where a smaller tsunami wave can be more devastating during a high tide than a larger wave at low tide. Tide gauges, found in most harbors, are the other tool for measuring tsunami wave height and period (wavelength).
What is the "wrap-around" effect?
Whether a tsunami is generated in the North or South Pacific, it has the potential to affect all shores of the Hawaiian Islands.  As large tsunami waves approach the islands, they may refract or bend around the islands and diffract through the channels between the islands as well.  The ability of a tsunami wave to bend around and through the islands is called the wrap-around effect.  During the wrap-around effect, the energy of the tsunami often decreases resulting in smaller wave heights.  Sometimes tsunami waves will reflect off of a land mass instead of bending around, thereby increasing wave height of the approaching wave.  Therefore, whether a tsunami warning is issued from an earthquake in Chile, Alaska, or Japan, inhabitants along all shores of the Islands should take the necessary precautions.
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Do all oceans have tsunamis?
Yes.  Tsunamis have been recorded in all the major oceans of the world. However, this phenomenon is mainly restricted to the Pacific basin, an area surrounded by volcanic island arcs, mountain chains and subduction zones earning the nickname the "ring of fire", as it is the most geologically active area on the planet.  The amount of activity in this region makes it much more susceptible to submarine faulting and subsequent tsunami events, whereas the Indian and Atlantic oceans are far less geologically active, with some exceptions, and therefore the occurrence of tsunamis is rare.
What is the Tsunami Warning System?
The lack of a warning during the 1946 tsunami that devastated many coastal areas in Hawaii, led scientists and governmental agencies to establish a Tsunami Warning System (TWS), for the Hawaiian Islands and United States territories in the Pacific by 1948. The main objectives of this system are: To detect and locate the existence of all possible tsunami-causing earthquakes by the use of properly monitored seismographs; to ensure that a tsunami actually exists by measuring water level changes at water level and tide-gauging stations located throughout the Pacific; and finally, to determine the time of arrival of the tsunami and to provide an adequate warning for evacuation procedures. The warning system has been expanded to include 24 ocean countries and is now called the Pacific Tsunami Warning Center. It also provides limited warning information for Indian Ocean coastal countries.
What is the difference between a Tsunami Watch and a Tsunami Warning?
A Tsunami Watch is automatically declared by the warning center for any earthquake having a magnitude of 7.5 or larger on the Richter scale (7.0 or larger in the Aleutian Islands) and located in an area where a tsunami can be generated. Notification of Civil Defense agencies begins, followed by limited public announcements by the local media. Data from sea level gauges is awaited for confirmation of the actual existence of a tsunami.
Reports on wave activity from the locations nearest to the earthquake epicenter is requested by the warning center. If there is no observed tsunami activity, the Tsunami Watch is canceled. If these stations report that a tsunami has been generated, a Tsunami Warning is issued for areas that may be impacted in the next three hours. At this time the public is informed of the ensuing danger by sirens and the emergency broadcast system. Evacuation procedures are implemented, and sea going vessels are advised to head out to sea, where in deep waters they will not be affected by the tsunami.
How many warnings have been issued by the Pacific Tsunami Warning Center since it was established?
The Pacific Tsunami Warning Center has issued a total of 20 warnings since it was first established in 1948.  Of these 20, 5 resulted in significant Pacific-wide tsunamis.  Even though all significant Pacific-wide tsunami events have been detected since 1948, 61 people perished when they failed to heed the warning for the 1960 tsunami that struck Hilo.  Since 1964, there have been no significant Pacific-wide tsunami events.
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What should I do or not do in a tsunami warning?
Because a tsunami can strike at any time, being adequately prepared and knowing what to do beforehand could save your life. Hawaii State and County Civil Defense agencies provide maps of evacuation zones and information on how to be prepared for this type of natural disaster in the front pages of the telephone book. If you are at the beach and you feel an earthquake or observe a rapid withdrawal of the sea, head for higher ground immediately. When a tsunami warning has been issued do not attempt to use the telephone or head to low-lying areas to view the oncoming waves. Remember, tsunamis travel at very fast speeds across the ocean; therefore once a warning has been issued you should evacuate immediately.
If I need to evacuate, what should I bring with me?
Your tsunami survival kit is generally the same for all natural disasters. Here is a list of suggested supplies:  an extra supply of prescription medicines, non-perishable dietary foods, ice chest, a minimum of 2 quarts of water per person per day, pet food, candles/flashlight, matches, blankets/sleeping bags, extra cash, clothing, eyeglasses, personal hygiene items, special items for infants, elderly and disabled family members, quiet games or books/toys for children, important papers-driver′s license, special medical information, insurance policies, and property inventories, First aid kit and water purification kit.
Can the arrival time of a tsunami be accurately predicted?
When a tsunami is generated offshore the wave will behave as a shallow water wave. A shallow water wave is one that travels through water having a depth less than 1/20 of its wavelength. Knowing that the average Pacific Ocean depth is roughly three miles, oceanographers can determine the speed of the tsunami, and calculate the time it will take to travel between any two points. This information led to the development of travel-time charts that make it possible to predict the arrival time of a tsunami wherever it is generated. Due to the high speeds of these waves, a tsunami can travel across the Pacific Ocean is less than one day! Areas near the epicenter of earthquakes, landslides or volcanic activity are most vulnerable to the effects of a tsunami as they cannot be properly warned by the Tsunami Warning Center of the coming danger.
What has been the most destructive tsunami to strike the Hawaiian Islands in recent history?
Early in the morning on April 1, 1946, an earthquake with a reported magnitude of 7.8 occurred in the Aleutian Islands off of Alaska. Almost five hours later the largest and most destructive tsunami waves in reported history struck the Hawaiian Islands. Maximum runups were reported to be 54 feet in Molokai and 55 feet in Pololu Valley on the Big Island. Waves in some areas penetrated more than half a mile inland. Between wave crests, the drawdown is reported to have exposed some areas of the seafloor 500 feet in the seaward direction. A total of 159 tsunami-related fatalities resulted from this destructive event. Many were curious school children who ventured into the exposed reef area, not knowing the receding water to be a sign of an approaching tsunami. No warning was feasible nor given for this tsunami.
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How many Pacific-wide tsunamis have struck the Hawaiian Islands in recent history?
In the 20th century, there were 13 significant tsunamis impacting Hawaii. These tsunamis were generated by earthquakes occurring along the geologically active margins of the Pacific basin. Maximum recorded runups were 55 feet on the Big Island and 54 feet on Molokai (see above) during the 1946 tsunami, and 53 feet in Kauai during the 1957 tsunami. The last hazardous Pacific-wide tsunami occurred in 1964.
How many locally generated tsunamis have occurred in the Hawaiian Islands in recent history?
On the Big Island there have been several significant tsunamis resulting from local earthquakes or submarine landslides.  The most recent and devastating of these tsunamis occurred in the early morning hours on November 29, 1975.  Within a little over an hour, two earthquakes jolted the island.  The first, located three miles inland of Kamoamoa village in Volcanoes National Park, had a Richter magnitude of 5.7.  The second, centered two miles offshore of the Wahaula heiau (also in the park area) was much more violent having a Richter magnitude later to be determined as 7.2.  The result of this earthquake was a 10 foot subsidence of the shoreline and the second most destructive local tsunami ever to be recorded in Hawaii.
Campers in the remote Volcanoes National Park coast at Halape were awakened by the violent shaking of the first quake unknowing that a second and more severe quake would follow in just over an hour later.  Some of them had barely gotten back to sleep when the second quake shook so violently that standing was nearly impossible.  Within 30 seconds, the first of five tsunami waves struck Halape.  Two campers, one an adult with a group of Boy Scouts, the other a fisherman, did not survive.   Nineteen others were injured.  The maximum runup height was 47 feet at Keauhou Landing and 26 feet at Halape, 1.9 miles to the southwest.
How are inundation/evacuation areas determined?
In Hawaii, methodology was developed at the University for determining the maximum expectable inundation of our shores for worst-case tsunamis, drawing on the records compiled by the Joint Institute for Marine and Atmospheric Research for many years.  These historical data are used in mathematical analyses to predict maximum wave heights along the coast; these heights are then used in numerical models involving the topography (land contours) to map the inundation in each location.
In coordination with the Civil Defense officers on each island, a final map is prepared showing the actual evacuation zones. The zones extend inland from the inundation limit to the nearest landmark such as a road, which can be used by public and police to identify the areas which must be evacuated to ensure safety. When the sirens sound, people are routed to safety until officials determine that hazardous wave action has ceased.
The zones are published in the front of the telephone directories for each Hawaiian island.  UH-scientists have recently done a similar analysis for the Humboldt Bay area in California which may be applied by their emergency management officials.  A few locations in Japan have well marked zones, based on historical inundation but for most of the Pacific, authorities simply call for evacuation of low lying areas.
It is interesting that for Hilo itself, there are such complete (block-by-block) records of inundation (1946-1964) that they have been used to determine evacuation zones with only minor analysis.  In fact, these records have been extensively used to test the computer models developed to predict tsunami wave heights and inundation.  If the model can adequately re-create a previous event, there is more assurance it can be used to predict future events elsewhere.
Since I don ′t live in an inundation area why should I be concerned?
The shoreline areas of the Hawaiian Islands are no doubt the main attraction for visitors and residents alike. Much of the state ′s commerce and recreation involves the surrounding ocean and therefore it is very important for all of us to acknowledge the threat a tsunami would impose on our lives. Even though you may live in an area that is not threatened by a tsunami directly, you would most definitely be impacted by its effects. The last Pacific-wide tsunami to impact Hawaii occurred over 40 years ago. During this period of tsunami quiescence, beach usage especially among children and teenagers has increased. It remains essential that this age group, having never experienced the destructive and deadly forced of tsunamis, be properly informed and aware of what to do and where to go in such an event.
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I own a boat, what should I do when there is a tsunami warning?
Boats are safer from tsunami damage while in the deep ocean rather than moored in a harbor.  U.S. Coast Guard guidelines suggest deployment to water depths of at least 1,200 feet (200 fathoms).  However, do NOT risk your life and attempt to get underway if it is too close to the first wave arrival time.  Anticipate slowdowns caused by traffic gridlock and hundreds of other boaters heading out to sea. Do NOT go near a harbor if there is a local tsunami.
If I would like more information on tsunamis who should I contact?
black ball Check out Links to other Tsunami Web Sites
black ball Pacific Tsunami Museum, P.O. Box 806, Hilo, HI 96721 Tel:(808)935-0926
black ball Pacific Tsunami Warning Center, 91-270 Fort Weaver Rd., Ewa beach, HI 96706 Tel: (808)689-8207 Ext. 301
black ball International Tsunami Information Center,737 Bishop St. Suite 2200, Honolulu, HI 96813 Tel:(808) 532-6422
Tsunami References
Looking for a good book or article about tsunamis? Check out our References webpage. We have compiled a list of books, scientific articles, technical reports, videos and maps as a starting point. Please let us know if you have some references that we ′re missing!
Libraries: Hilo, Kailua-Kona, Lihue, Kahului, Kahuku, Hawaii Kai, Waianae, Hawaii State Library, Salt Lake, and Molokai.
For more information e-mail at or call the Hawaii State Public Library System, Program Coordinator at (808) 586-3620.



All materials © Copyright 1996-2007 Pacific Tsunami Museum Inc.
130 Kamehameha Ave Hilo, HI 96720 tel: 808-935-0926 FAX: 808-935-0842 email:
Last Revised November 2007