U.S. Tsunami Programs: A Brief Overview
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Hawaii has a long history of damaging tsunamis. Its tsunami record includes events caused by earthquakes both near and far. Significant tsunamis were produced locally in and , but the majority of Hawaii's destructive tsunamis were produced by distant subduction zone earthquakes. Notable distant tsunamis came from Chile , , , Russia , , Alaska , , and Japan Underwater landslides also pose a threat, and volcanic activity was responsible for a tsunami in Historically, tsunamis in American Samoa have originated around the Pacific, but the greatest threat is from the nearby Tonga trench.
This was made clear in , when an earthquake near this subduction zone produced the worst tsunami in the territory's recorded history. Guam and the Northern Mariana Islands have been struck by tsunamis from sources both local and distant Japan and Russia, most notably. The region's largest tsunami on record was produced by a large earthquake off Guam in The greatest threat is from the nearby Marianas trench, another significant subduction zone.
Atlantic tsunami hazard is greatest for Puerto Rico and the U. Just to the north of the islands, in the Atlantic Ocean, lies the Puerto Rico trench, a dangerous subduction zone like those in the Pacific.
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However, most of the recorded tsunamis in the region were produced by local earthquakes outside of the trench, most notably in and , or in the broader Caribbean region, like off the coast of Hispaniola , , Tsunamis caused by distant earthquakes, volcanic activity, and underwater landslides may also affect the region. The history of U. Atlantic Coast tsunamis is short, but shows that tsunamis can happen in the region.
Key events include an earthquake and an underwater landslide that both produced small local tsunamis. Also, a tsunami produced by an earthquake-generated landslide off Newfoundland, Canada recorded as small waves along the U. There is no subduction zone along the U. Atlantic Coast, and earthquakes are not as large or as frequent as in other regions.
Underwater landslides and meteotsunamis are the most likely source of tsunami waves in the region. More distant tsunami threats come from the Puerto Rico trench, the Canary Islands, and the Azores-Gibraltar fault zone. Atlantic Coast, the U. Gulf Coast is not near a subduction zone, and there has not been much tsunami or seismic activity recorded in the region. Still, evidence suggests a tsunami is possible. An earthquake off Puerto Rico produced the only tsunami on record for the Gulf Coast. However, the geography of the Gulf may reduce the impact of most distant tsunamis.
Geologic evidence in the Gulf of Mexico points to underwater landslides as the region's likeliest tsunami source. Understanding the hazard is an important first step in understanding risk. More research remains to be done to better understand the hazard and the potential losses.
These hazard levels are based on brief and incomplete historical records. It will not look like a normal wind wave. Tsunamis rarely become great towering breaking waves. Sometimes, before the water rushes on land, it will suddenly recede, showing the ocean floor, reefs, and fish like a very low, low tide. Large tsunamis may continue for days in some locations, reaching their peak often a couple of hours after arrival and gradually tapering off after that.
Dangerous tsunami currents can last for days. Tsunamis are often referred to as local or distant. The type of tsunami depends on the location of the source of the tsunami and where it may strike land. The source of a local tsunami is close to the coast and may arrive in less than one hour. The danger is greatest for local tsunamis because warning time is limited.
A distant tsunami is generated far away from a coast, so there is more time to issue and respond to warnings. Most ocean waves are generated by wind. Tsunamis are not the same as wind waves. First of all, they have different sources. In addition, tsunamis move through the entire water column, from the ocean surface to the ocean floor, while wind waves only affect the ocean surface.
Waves can also be described based on their wavelength horizontal distance between wave crests , period time between wave crests , and speed.
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These characteristics highlight additional differences between tsunamis and wind waves. Wavelengths are measured in miles for tsunamis and in feet for wind waves. Periods are measured in minutes for tsunamis and in seconds for wind waves. Tsunamis are also faster than wind waves, and although they may be smaller in height in the deep ocean, tsunamis can grow to much greater heights and cause much more destruction than wind waves at the coast.
Tsunami Wind Wave Source Earthquakes, landslides, volcanic activity, certain types of weather, near earth objects Winds that blow across the surface of the ocean Location of energy Entire water column, from the ocean surface to the ocean floor Ocean surface Wavelength miles feet Wave Period 5 minutes — 2 hours seconds Wave Speed miles per hour in deep water miles per hour near shore miles per hour.
Tsunami Warning Center History
The main mission of the warning centers is to help protect life and property from tsunamis. To do this, they monitor observational networks, analyze earthquakes, evaluate water-level information, issue tsunami messages, conduct public outreach, and coordinate with the National Tsunami Hazard Mitigation Program and government, academic, and international organizations to continually improve their operations. The Tsunami Warning Centers depend on an observation system that includes seismic and water-level networks from around the world to help them determine when and where to issue tsunami messages.
The warning centers analyze this information to determine if the earthquake could have generated a tsunami and if a tsunami message is necessary. Water-Level Networks —If an earthquake meets certain criteria, the warning centers turn to water-level information, looking for changes in water-level height that could indicate the existence and size of a tsunami.
The primary sources of information about water-level change are a network of Deep-ocean Assessment and Reporting of Tsunami DART systems and an extensive array of coastal water-level stations. Each system consists of a bottom pressure recorder BPR anchored on the ocean floor and a separately moored companion surface buoy. When a tsunami passes over a BPR, the instrument detects and records the changes in the overlying water pressure. An acoustic link transmits information from the BPR to the surface buoy, which then relays it via satellite to the warning centers where the information is incorporated into tsunami forecast models.
See how a DART system works video. Coastal water-level stations collect important information about the height of the ocean at specific coastal locations. Their primary purpose is to monitor tides for navigation purposes, thus they are located on the coast in contrast to the DART systems, which are in deep water , generally on piers in harbors. Information from these stations is relayed via satellite to the warning centers where it is used to confirm tsunami arrival time and height and is incorporated into tsunami forecast models.
Coastal water-level stations are owned and operated by a number of national and international organizations. In the United States, most of the tsunami-capable coastal water-level stations i. In most cases, the first sign of a potential tsunami is an earthquake. Seismic waves travel about times faster than tsunamis, so information about an earthquake is available before information about any tsunami it may have generated.
Three key pieces of information about an earthquake help the Tsunami Warning Centers determine if it was capable of generating a tsunami: The warning centers use this preliminary seismic information to decide if they should issue a tsunami message and at what alert level s. Once a message is issued, the warning centers conduct additional seismic analysis and run tsunami forecast models using information from the seismic and water-level networks as it becomes available. These numerical models use the real-time information and pre-established scenarios to simulate tsunami movement across the ocean and estimate coastal impacts, including wave height and arrival times, the location and extent of coastal flooding, and event duration.
The resulting forecasts, combined with historic tsunami information and additional seismic analysis, help the warning centers decide if they should issue an updated or cancellation message. It is more difficult to forecast nonseismic tsunamis like landslide and volcanic tsunamis and meteotsunamis , which can arrive with little to no warning. Even if a nonseismic tsunami is detected by a DART system or coastal water-level station, there may not be time to develop a detailed forecast. In the case of meteotsunamis, NWS Weather Forecast Offices, with decision support from the warning centers, can notify the public of the potential coastal threat given the presence of or potential for certain weather conditions along with observed water-level measurements.
Tsunami messages are issued by the Tsunami Warning Centers to notify emergency managers and other local officials, the public, and other partners about the potential for a tsunami following a possible tsunami-generating event.
The U.S. Tsunami Program: A Brief Overview. Peter Folger. Specialist in Energy and Natural Resources Policy. March 18, Congressional. Read chapter Summary: Many coastal areas of the United States are at risk for of the U.S. Tsunami Program and the Nation's Preparedness Efforts ().
There are four levels of tsunami alerts: Initial tsunami messages include alert level s , preliminary information about the earthquake, and an evaluation of the threat. If a tsunami is already suspected, the message may also include wave arrival times, recommended life safety actions, and potential impacts. Subsequent messages, both updates and cancellations, are based on additional seismic analysis and results from the tsunami forecast models and may feature more refined, detailed, and targeted information.
A tsunami warning is issued when a tsunami with the potential to generate widespread inundation is imminent, expected, or occurring. Warnings alert the public that dangerous coastal flooding accompanied by powerful currents is possible and may continue for several hours after initial arrival. Warnings 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 coastal areas and the repositioning of ships to deep waters when there is time to safely do so.
Warnings may be updated, adjusted geographically, downgraded, or canceled based on updated information and analysis. A tsunami advisory is issued when a tsunami with the potential to generate strong currents or waves dangerous to those in or very near the water is imminent, expected, or occurring.
The threat may continue for several hours after initial arrival, but significant inundation is not expected for areas under an advisory. Appropriate actions to be taken by local officials may include closing beaches, evacuating harbors and marinas, and the repositioning of ships to deep waters when there is time to safely do so. Advisories may be updated, adjusted geographically, upgraded to a warning, or canceled based on updated information and analysis. A tsunami watch is issued when a tsunami may later impact the watch area.
The watch may be upgraded to a warning or advisory or canceled based on updated information and analysis. Emergency management officials and the public should prepare to take action. A tsunami information statement is issued when an earthquake or tsunami has occurred of interest to the message recipients. In most cases, information statements are issued to indicate there is no threat of a destructive basin-wide tsunami and to prevent unnecessary evacuations. Information statements for distant events requiring evaluation may be upgraded to a warning, advisory, or watch based on updated information and analysis.
A tsunami threat message is a tsunami message for international partners in the Pacific and Caribbean. The United States does not issue alerts for these partners. The primary purpose of these messages is to help national authorities understand the threat to their coasts so they can determine which alerts to issue for their coastlines, if any. A threat message describes tsunami threats according to the potential hazard and impact to people, structures, and ecosystems on land or in nearshore marine environments.
National authorities will determine the appropriate level of alert for each country and may issue additional or more refined information and instructions. A threat message may be updated based on new information, data, and analysis.
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An information statement may be issued following an earthquake or tsunami of interest to the message recipients if there is little to no threat, but may be upgraded to a tsunami threat message if warranted. The Tsunami Warning Centers prepare and issue tsunami messages for their respective designated service areas.
Coast Guard, the U. Each of these recipients is responsible for forwarding the message to its own constituents.
The Tsunami Warning Centers issue a cancellation after they determine that a destructive tsunami will not affect an area under a warning, advisory, or watch or that a tsunami has diminished to a level where additional damage is not expected. However, the cancellation of a message does not mean the area is safe. The final decision that an area is safe is up to local and state emergency management officials. Pacific and Caribbean territories, and the British Virgin Islands and is the primary international forecast center for the warning systems of the Intergovernmental Oceanographic Commission of the United Nations Educational, Scientific, and Cultural Organization in the Pacific and the Caribbean and Adjacent Regions.
The Tsunami Warning Centers base their initial tsunami messages on the preliminary earthquake information location, depth, and magnitude received from seismic networks since that is all the information available within the first few minutes after an earthquake. They use preset criteria Atlantic , Pacific to decide when to issue a tsunami message and what alert s to include.
Subsequent messages and alerts are based on impact estimation resulting from additional seismic analysis, water-level measurements, tsunami forecast model results, and historical tsunami information. Tsunami warnings are typically issued following coastal earthquakes magnitude 6. Tsunami height also affects alert selection.
In general, the warning centers issue a tsunami warning if the forecast or observed tsunami height exceeds 1. In regions of high seismic network density, the warning centers can issue messages within five minutes. In areas of lower seismic network density, response time increases to minutes.
They may also come through outdoor sirens, local officials, emails and text message alerts from state and local opt-in systems, and telephone notifications. There may not always be enough time for an official warning, so it is important to understand natural warnings. Learn how to get alerts from the Tsunami Warning Centers. A tsunami is one the most powerful and destructive natural forces. It can produce unusually strong currents, rapidly flood land, and devastate coastal communities. Low-lying areas such as beaches, bays, lagoons, harbors, river mouths, and areas along rivers and streams leading to the ocean are the most vulnerable.
Most tsunami damage and destruction is caused by flooding, wave impacts, strong currents, erosion, and debris. The water can be just as dangerous as it returns to the sea, taking debris and people with it. In addition to loss of life and mass injuries, other potential impacts include damage to and destruction of homes and businesses, cultural and natural resources, infrastructure, and critical facilities. Flooding and dangerous currents can last for days. Even small tsunamis can pose a threat.
Strong currents can injure and drown swimmers and damage and destroy boats in harbors. Local tsunamis are particularly dangerous. They can strike a coast within minutes of generation with little or no warning. Although tsunamis cannot be prevented, there are things you can do before a tsunami that could save your life and the lives of your family and friends.
Importantly, find out if your home, school, workplace, or other places you visit often are in a tsunami hazard zone U.
- U.S. Tsunami Warning Centers;
- ITIC Training Program - International Tsunami Information Center.
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If you live or spend time in a tsunami hazard zone: Educate yourself about tsunami warnings official and natural and ensure you have multiple ways to receive official warnings. In the United States, get a NOAA Weather Radio , sign up for text message alerts from your local government, and verify that your mobile devices receive wireless emergency alerts.
Make an emergency plan that includes plans for family communication and evacuation. Map out routes from home, work, and other places you visit often to safe places on high ground or inland away from the water and outside the tsunami hazard zone. Your community may already have identified evacuation routes and assembly areas if they have not, identify a safe place at least feet above sea level or 1 mile inland.
Plan to evacuate on foot if you can; roads may be impassable due to damage, closures, or traffic jams. Practice walking your routes, even in darkness and bad weather. This will ease evacuation during an emergency.
NTHMP - U.S. Tsunami Hazard
Put together a portable disaster supplies kit with items you and your family including pets may need in an emergency. Prepare kits for work and cars, too. Be a role model. Share your knowledge and plans with others. If you are visiting the coast, find out about local tsunami safety. Your hotel or campground should have this information. There are two ways that you may be warned that a tsunami is coming: Both are equally important.
You may not get both. It may also come through outdoor sirens, local officials, emails and text message alerts from state and local opt-in systems, and telephone notifications. There may not always be time to wait for an official tsunami warning. A natural tsunami warning may be your first, best, or only warning that a tsunami is on its way. Natural tsunami warnings include strong or long earthquakes, a loud roar like a train or an airplane from the ocean, and unusual ocean behavior. The ocean could look like a fast- rising flood or a wall of water bore. Or, it could recede suddenly, showing the ocean floor, reefs, and fish like a very low, low tide.
If you experience any of these warnings, even just one, a tsunami could be coming. How you should respond to a tsunami warning depends on where you are and the type of warning you receive i. Be prepared to respond immediately to whatever you hear or see first. If you are in a tsunami hazard zone and receive an official tsunami warning: Stay out of the water and away from beaches and waterways. Get more information from radio, television, or your mobile device text or data and continue to stay informed throughout the event. If officials ask you to evacuate, implement your emergency plan and move quickly to your safe place.
If you do not have a safe place or cannot reach it, follow evacuation signs to safety or go as high or as far inland away from the water as possible at least feet above sea level or a mile inland. If you are in a tsunami hazard zone and receive a natural tsunami warning, a tsunami could arrive within minutes: In case of an earthquake, protect yourself.
Drop, cover, and hold on. Be prepared for aftershocks. Each time the earth shakes, drop, cover, and hold on. Do not wait for an official warning or instructions from officials. As soon as you can move safely, implement your emergency plan and move quickly to your safe place. If there is earthquake damage, avoid fallen power lines and stay away from weakened structures.
When you are in a safe place, get more information from radio, television, or your mobile device text or data. If you are on the beach or near water and feel an earthquake of any size and length, move quickly to high ground or inland away from the water as soon as you can move safely. Get more information from radio, television, or your mobile device text or data.
If you are outside of the tsunami hazard zone and receive a warning, stay where you are unless officials tell you otherwise. For your safety and others, always follow instructions from local officials and stay out of the tsunami hazard zone until they tell you it is safe.
In the United States, to find out if you are in a tsunami hazard zone, visit the Tsunami Maps web page.