Tsunamis, also known as seismic sea waves, are powerful natural phenomena. How Fast Do Tsunamis Travel? Understanding tsunami speed is crucial for coastal safety and effective warning systems. This educational resource from TRAVELS.EDU.VN provides comprehensive insights into tsunami characteristics, detection, and safety measures, ensuring you’re prepared and informed. By understanding ocean currents, tsunami propagation, and wave dynamics, we can better mitigate the impact of these devastating events.
1. General Tsunami Information
1.1 What is a Tsunami?
A tsunami is a series of extremely long waves caused by a large and sudden displacement of the ocean. These waves can travel across entire ocean basins, causing dangerous coastal flooding and powerful currents that can last for hours or days. Imagine waves with crests spaced tens to hundreds of miles apart – that’s the scale of a tsunami.
1.2 What is the Origin of the Word “Tsunami?”
The word “tsunami” originates from the Japanese characters for harbor (“tsu”) and wave (“nami”).
1.3 Is a Tsunami the Same as a Seismic Sea Wave or a Tidal Wave?
A tsunami is a seismic sea wave if it’s generated by an earthquake. However, tsunamis can also be caused by non-seismic disturbances like landslides or volcanic eruptions. The term “tsunami” is internationally recognized for waves caused by any large and sudden ocean displacement. It’s important to note that tsunamis are not related to tides, which are caused by the gravitational pull of the Sun and Moon. Therefore, calling a tsunami a tidal wave is inaccurate.
1.4 Can Tsunamis Be Predicted?
Scientists cannot predict exactly when and where the next tsunami will strike, similar to predicting earthquakes. However, Tsunami Warning Centers monitor seismic activity and can issue tsunami messages when they believe a tsunami is possible. Once a tsunami is detected, forecast models are used to predict wave height, arrival times, and potential flooding. In cases where the source is close to the coast, immediate natural warnings should be recognized and responded to.
1.5 How Often Do Tsunamis Happen?
Tsunamis that cause damage or deaths near their source occur approximately twice per year. Those that cause damage or deaths on distant shores happen about twice per decade, according to the Global Historical Tsunami Database.
1.6 Where Do Tsunamis Happen?
Tsunamis can occur in any large body of water, including oceans and inland seas. While they’ve caused damage and deaths worldwide, certain areas are more prone due to their proximity to tsunami sources, ocean floor depth and shape (bathymetry), and coastal elevation and features (topography). The Pacific Ocean, with its geologically active “Ring of Fire,” accounts for about 78% of confirmed tsunami events between 1900 and 2015.
Since 1900, Japan has experienced the highest percentage of tsunamis (21%), followed by Russia and Indonesia (8% each). While many are small and localized, some can cause significant damage on distant shores. Significant distant tsunamis since 1900 have originated off Alaska, Chile, Japan, Indonesia, Pakistan, and Russia.
1.7 Where Can Tsunamis Happen in the United States?
Any U.S. coast can be struck by a tsunami, but the hazard level varies. This assessment is based on historical records, geological evidence, and proximity to tsunami sources.
| Region | Hazard Level |
|---|---|
| U.S. West Coast | High to Very High |
| Alaska (Southern Coast) | High to Very High |
| Alaska Arctic Coast | Very Low |
| Hawaii | High to Very High |
| American Samoa | High |
| Guam and Northern Mariana Islands | High |
| Puerto Rico/U.S. Virgin Islands | High |
| U.S. Atlantic Coast | Very Low to Low |
| U.S. Gulf Coast | Very Low |
Coastlines near subduction zones face the greatest risk due to large earthquakes and associated landslides. The U.S. East and Gulf Coasts are less prone to large earthquakes, making underwater landslides and meteotsunamis the more likely sources.
1.7.1 What is the Tsunami Hazard Level for Anchorage and the Upper Cook Inlet in Alaska?
Compared to the Southern Coast of Alaska, Anchorage and the upper Cook Inlet have a very low tsunami hazard level. Tsunamis entering the upper Cook Inlet from the Gulf of Alaska or lower Cook Inlet are weakened by the relatively shallow water, diminishing their dangerous potential.
1.8 What Are Some of the Most Damaging Tsunamis to Affect the United States?
As of January 2018, the Global Historical Tsunami Database lists 30 reported tsunamis that caused at least one death or $1 million in damage (2017 dollars) affecting U.S. states and territories.
| Region | Local Tsunami* | Distant Tsunami* |
|---|---|---|
| U.S. West Coast | 1820, 1878, 1894, 1930 | 1946, 1952, 1957, 1960, 1964, 1975, 2006, 2010, 2011 |
| Alaska | 1788, 1845, 1853, 1900, 1917, 1946, 1957, 1958, 1964, 1994 | 1960 |
| Hawaii | 1868, 1975 | 1837, 1868, 1877, 1923, 1946, 1952, 1957, 1960, 1964, 2011, 2012 |
| American Samoa | 2009 | 1946, 1960 |
| Guam and Northern Mariana Islands | 1849 | — |
| Puerto Rico/U.S. Virgin Islands | 1867, 1918 | — |
*See section 3.6 for the difference between local and distant tsunamis.
1.9 When Do Tsunamis Happen?
Tsunamis can happen at any time, in any season, and during any weather conditions. There’s no specific “tsunami season.”
1.10 Where Can I Learn More About Tsunamis?
Numerous online resources offer more information about tsunamis, including:
- The COMET Program’s Tsunami Distance Learning Course
- National Weather Service’s JetStream Online Weather School
- National Weather Service’s Tsunami Safety website
- International Tsunami Information Center
- Global Historical Tsunami Database
- The TsunamiZone
2. Causes of a Tsunami
2.1 What Causes a Tsunami?
A tsunami is triggered by a large and abrupt displacement of the ocean. While large earthquakes below or near the ocean floor are the most common cause, other factors like landslides, volcanic activity, certain weather conditions, and even near-Earth objects can also cause tsunamis. According to the Global Historical Tsunami Database, about 88% of tsunamis are generated by earthquakes or earthquake-induced landslides.
2.2 How Do Earthquakes Generate Tsunamis?
Earthquakes generate tsunamis through sudden movements in the water column. Key factors include the earthquake’s location, magnitude, and depth. Most tsunamis are generated by earthquakes with magnitudes over 7.0 that occur under or very near the ocean (usually at or near subduction zones) and less than 100 kilometers (62 miles) below the Earth’s surface. Generally, an earthquake must exceed magnitude 8.0 to generate a dangerous distant tsunami.
An earthquake must be big enough and close enough to the ocean floor to cause vertical movement, setting a tsunami in motion. As the ocean floor rises or drops, so does the water above it, creating waves that radiate out in all directions. The amount of ocean floor movement, the size of the affected area, and the water depth at the source all influence the size of the resulting tsunami. Earthquakes can also cause landslides that generate tsunamis.
Examples of earthquake-generated tsunamis:
- March 11, 2011, Honshu Island, Japan: A magnitude 9.1 earthquake generated a devastating tsunami that impacted the entire Pacific. In Japan, it displaced over 500,000 people, caused approximately $236 billion (2016 dollars) in damage, and led to a nuclear accident. The tsunami reached heights of 128 feet and traveled almost five miles inland.
- December 26, 2004, Northern Sumatra, Indonesia: A magnitude 9.1 earthquake triggered the deadliest tsunami in history, impacting 15 countries in Southeastern and Southern Asia and Eastern and Southern Africa. It resulted in approximately 230,000 deaths, displaced 1.7 million people, and caused roughly $13 billion (2016 dollars) in economic losses.
- March 27, 1964, Prince William Sound, Alaska: A magnitude 9.2 earthquake (the largest recorded in U.S. history) generated tsunamis that devastated coastal communities in Alaska with waves as high as 167 feet. The damage was approximately $1 billion (2016 dollars), and about 124 deaths were attributed to the tsunami.
- April 1, 1946, Aleutian Islands, Alaska: A magnitude 8.6 earthquake generated a tsunami that caused widespread destruction across the Pacific. Most of the 167 lives lost and $322 million (2016 dollars) in damage were in Hawaii, where waves reached heights of 55 feet.
- November 1, 1755, Lisbon, Portugal: A magnitude 8.5 (estimated) earthquake in the Atlantic Ocean generated a tsunami that affected the coasts of Portugal, Spain, North Africa, and the Caribbean, resulting in an estimated 50,000 deaths.
- January 26, 1700, Cascadia Subduction Zone: A magnitude 9.0 (estimated) earthquake generated a tsunami that inundated the coasts of Cascadia (northern California, Oregon, Washington, and southern British Columbia) as well as coastal villages in Japan.
To learn more about earthquakes, visit the U.S. Geological Survey’s Earthquake Hazards Program.
2.2.1 What Types of Earthquakes Generate Tsunamis?
Most tsunamigenic earthquakes occur on thrust or reverse faults in subduction zones. However, 10-15 percent of damaging tsunamis are generated by strike-slip earthquakes, where the movement is horizontal. These tsunamis are often caused by associated landslides, sloping ocean floor movement, or the presence of seamounts. Tsunamis generated by strike-slip earthquakes usually affect regions near the source only.
2.2.2 What Was the Largest Earthquake Ever Recorded?
The largest earthquake ever recorded was a magnitude 9.5 earthquake off the coast of Southern Chile on May 22, 1960. The second largest was the 1964 magnitude 9.2 in Prince William Sound, Alaska, both generating devastating tsunamis.
2.3 How Do Landslides Generate Tsunamis?
Landslides, including rock falls, slope failures, debris flows, slumps, ice falls/avalanches, and glacial calving, can generate tsunamis when they enter the water and displace it. The generation depends on the amount of landslide material, its speed, and the depth it moves to. Landslide-generated tsunamis may be larger than seismic tsunamis near their source but lose energy quickly and rarely affect distant coastlines.
Most landslides that generate tsunamis are caused by earthquakes, but other forces can also cause them. A landslide-generated tsunami can occur independently or alongside an earthquake-generated tsunami, complicating the warning process.
Examples of landslide-generated tsunamis:
- July 17, 1998, Papua New Guinea: A magnitude 7.0 earthquake triggered a large underwater landslide, generating a deadly tsunami with waves reaching roughly 49 feet high. Approximately 2,200 lives were lost, and more than 10,000 people were displaced.
- July 10, 1958, Southeast Alaska: A magnitude 7.8 earthquake triggered landslides, rock falls, and ice falls that generated tsunamis that killed five people. A rock fall into Lituya Bay sent water surging over the opposite shore, reaching a maximum height of 1,720 feet, considered the largest tsunami ever recorded.
- November 18, 1929, Grand Banks, Newfoundland, Canada: A magnitude 7.3 earthquake triggered a submarine landslide, generating a tsunami with waves up to 43 feet high, causing 28 deaths and $14 million (2016 dollars) in damage.
To learn more about landslides, visit the U.S. Geological Survey’s Landslide Hazards Program.
2.4 How Do Volcanoes Generate Tsunamis?
Volcanoes can generate tsunamis through:
- Pyroclastic flows
- Submarine explosions
- Caldera formation
- Landslides
- Lateral blasts
Volcanic tsunamis, like landslide tsunamis, usually lose energy quickly and rarely affect distant coastlines.
Examples of volcano-generated tsunamis:
- August 27, 1883, Indonesia: The Krakatau volcano exploded and collapsed, generating one of the largest tsunamis ever recorded, killing more than 34,000 people.
- May 21, 1792, Kyushu Island, Japan: A flank collapse of the Unzen volcano generated a tsunami with waves reaching 180 feet high, causing more than 14,000 deaths.
- ~1610 BC, Greece: The volcano Santorini erupted, generating a tsunami that swept the shores of nearby islands and contributed to the end of the Minoan culture on Crete.
To learn more about volcanoes, visit the U.S. Geological Survey’s Volcano Hazards Program.
2.5 How Does Weather Generate Tsunamis?
Air pressure disturbances, often associated with fast-moving weather systems like squall lines, can generate tsunamis called “meteotsunamis.” These are similar to earthquake-generated tsunamis and depend on the intensity, direction, and speed of the air pressure disturbance, as well as the ocean’s depth. Meteotsunamis are regional, and certain areas are prone to them due to local weather patterns and the shape of the Earth’s surface.
Examples of meteotsunamis:
- June 13, 2013, Northeastern United States: Tsunami-like waves crashed upon the New Jersey and southern Massachusetts coasts due to a derecho.
- June 21, 1978, Vela Luka, Croatia: Flooding waves inundated the port town of Vela Luka due to an atmospheric disturbance, resulting in 19.5-foot waves and millions of dollars in damage.
2.6 Can Near Earth Objects Generate Tsunamis?
It’s very rare for near-Earth objects like asteroids or comets to cause tsunamis. Scientists believe large objects (approximately 1,000 meters or 0.62 miles in diameter) could hit the ocean and generate an “impact” tsunami. Smaller objects that explode in the atmosphere could generate an “airburst” tsunami.
3. Tsunami Characteristics
3.1 How Many Waves Are There in a Tsunami?
A tsunami is a series of waves, not just one, often referred to as the tsunami wave train. A large tsunami may continue for days in some locations.
3.2 How Fast Does a Tsunami Travel?
How fast do tsunamis travel? Tsunami speed depends on the water depth. In the deep ocean, tsunamis can move as fast as a jet plane, over 500 mph, and can cross entire oceans in less than a day. As they enter shallow water near land, they slow to the speed of a car, approximately 20 to 30 mph.
Tsunami speed can be calculated by taking the square root of the product of the water depth and the acceleration of gravity (32.2 feet per second squared). In 15,000 feet of water, this works out to about 475 miles per hour. At these speeds, a tsunami will travel from the Aleutian Islands to Hawaii in about five hours or from the Portugal coast to North Carolina in eight and a half hours.
3.3 How Big Is a Tsunami?
In the deep ocean, a tsunami’s wavelength may be hundreds of miles, but its waves are barely noticeable and rarely more than three feet high. Mariners at sea won’t usually notice them. As the waves enter shallow water and slow down, their wavelengths decrease, their height grows, and currents intensify. When they strike land, most tsunamis are less than 10 feet high, but can exceed 100 feet in extreme cases. A large tsunami can flood low-lying coastal areas more than a mile inland.
3.4 What Does a Tsunami Look Like When It Reaches the Coast?
When a tsunami reaches the coast, it may look like a fast-rising flood or a wall of water. Its appearance may differ along a coast and won’t look like a normal wind wave. Tsunamis rarely become towering breaking waves. Sometimes, the water will suddenly recede, revealing the ocean floor.
3.5 How Long Does a Tsunami Last?
Large tsunamis may continue for days in some locations, reaching their peak a couple of hours after arrival and gradually tapering off. The time between tsunami crests ranges from approximately five minutes to two hours. Dangerous tsunami currents can last for days.
3.6 What Is the Difference Between a Local and a Distant Tsunami?
Tsunamis are often categorized as local or distant. A local tsunami originates close to the coast and may arrive in less than one hour, offering limited warning time. A distant tsunami is generated far away, providing more time to issue and respond to warnings.
3.7 How Are Tsunamis Different From Normal Ocean Waves?
Tsunamis differ from wind waves in their sources, the depth of water they affect, and their wavelengths, periods, and speeds. Tsunamis move through the entire water column, while wind waves only affect the ocean surface.
| Characteristic | Tsunami | Wind Wave |
|---|---|---|
| Source | Earthquakes, landslides, volcanic activity, certain weather, near-Earth objects | Winds blowing across the ocean surface |
| Location of energy | Entire water column | Ocean surface |
| Wavelength | 60-300 miles | 300-600 feet |
| Wave Period | 5 minutes – 2 hours | 5-20 seconds |
| Wave Speed | 500-600 miles per hour (in deep water); 20-30 miles per hour (near shore) | 5-60 miles per hour |
4. Tsunami Detection and Forecasting
4.1 What Are the Responsibilities of the Tsunami Warning Centers?
The NWS operates two Tsunami Warning Centers staffed 24/7. Their mission is to protect life and property from tsunamis by monitoring observational networks, analyzing earthquakes, evaluating water-level information, issuing tsunami messages, conducting public outreach, and coordinating with other organizations.
4.2 How Are Tsunamis Detected?
Tsunami Warning Centers rely on a network of seismic and water-level monitoring systems worldwide.
- Seismic Networks: Provide information about an earthquake’s location, depth, magnitude, and other characteristics.
- Water-Level Networks: Include Deep-ocean Assessment and Reporting of Tsunami (DART) systems and coastal water-level stations.
4.3 What Is a DART System?
DART (Deep-ocean Assessment and Reporting of Tsunami) systems are designed for early detection, measurement, and real-time reporting of tsunamis in the open ocean. The U.S. network includes 39 systems strategically located throughout the Pacific and Atlantic Oceans, the Gulf of America, and the Caribbean Sea.
Each system includes a bottom pressure recorder (BPR) on the ocean floor and a surface buoy. The BPR detects changes in water pressure, transmitting the data to the surface buoy, which relays it to the warning centers via satellite.
4.4 What Is a Coastal Water-Level Station?
Coastal water-level stations monitor ocean height at specific locations, primarily for navigation purposes. Located on the coast, they relay information to the warning centers to confirm tsunami arrival time and height, contributing to tsunami forecast models.
4.5 How Are Tsunamis Forecast?
Forecasting begins with earthquake analysis. The Tsunami Warning Centers use earthquake information (location, depth, and magnitude) to determine if a tsunami message is needed. Once issued, they conduct additional seismic analysis and run tsunami forecast models using data from seismic and water-level networks. These models simulate tsunami movement and estimate coastal impacts.
Forecasting non-seismic tsunamis is more difficult due to limited warning. In the case of meteotsunamis, NWS Weather Forecast Offices notify the public of potential threats based on weather conditions and water-level measurements.
5. Tsunami Messages
5.1 What Are Tsunami Messages?
Tsunami messages are issued by the Tsunami Warning Centers to notify emergency managers, local officials, the public, and other partners about the potential for a tsunami. For the United States, Canada, and the British Virgin Islands, these messages include alerts with four levels: warning, advisory, watch, and information statement.
Initial messages include alert level(s), earthquake information, and threat evaluation. Subsequent messages may include wave arrival times, recommended actions, and potential impacts.
5.1.1 What is a Tsunami Warning?
A tsunami warning is issued when a tsunami with the potential to generate widespread inundation is imminent, expected, or occurring. It alerts the public that dangerous coastal flooding and powerful currents are possible.
5.1.2 What is a Tsunami Advisory?
A tsunami advisory is issued when a tsunami with the potential to generate strong currents or waves dangerous to those in or near the water is imminent, expected, or occurring. Significant inundation is not expected.
5.1.3 What is a Tsunami Watch?
A tsunami watch is issued when a tsunami may later impact the watch area, allowing time to prepare.
5.1.4 What is a Tsunami Information Statement?
A tsunami information statement is issued when an earthquake or tsunami has occurred, but there is no threat of a destructive basin-wide tsunami, preventing unnecessary evacuations.
5.2 What is a Tsunami Threat Message?
A tsunami threat message is for international partners, describing tsunami threats according to the potential hazard and impact. National authorities determine appropriate alert levels.
5.3 Who Issues Tsunami Messages?
The Tsunami Warning Centers issue tsunami messages for their designated service areas, including NWS Weather Forecast Offices, state emergency operations centers, the U.S. Coast Guard, and designated international authorities.
5.4 Who Cancels Tsunami Messages?
The Tsunami Warning Centers issue cancellations when a destructive tsunami is no longer expected or has diminished. However, local and state emergency management officials make the final decision on when an area is safe.
5.5 What Are the Designated Service Areas of the Tsunami Warning Centers?
- The National Tsunami Warning Center in Palmer, Alaska, serves the continental United States, Alaska, and Canada.
- The Pacific Tsunami Warning Center in Honolulu, Hawaii, serves the Hawaiian Islands, U.S. Pacific and Caribbean territories, and the British Virgin Islands.
5.6 How Do the Tsunami Warning Centers Decide What Alert Levels to Include in Their Messages?
Tsunami Warning Centers base their messages on preliminary earthquake information and preset criteria. Subsequent messages and alerts are based on impact estimation from seismic analysis, water-level measurements, tsunami forecast model results, and historical data.
5.7 How Quickly Are Tsunami Messages Issued?
The time to issue a tsunami message depends on the seismic network density near the earthquake’s origin. It can take as little as five minutes in regions with high density, and 10-15 minutes in areas with lower density.
5.8 How Can I Receive Tsunami Messages?
In the United States, tsunami messages are broadcast through local radio and television, marine radio, wireless emergency alerts, NOAA Weather Radio, NOAA websites (like Tsunami.gov), and social media. They may also come through outdoor sirens, local officials, emails, text message alerts, and telephone notifications.
6. Tsunami Safety
6.1 Why Are Tsunamis Dangerous?
Tsunamis can produce strong currents, rapidly flood land, and devastate coastal communities. Low-lying areas like beaches, bays, harbors, river mouths, and areas along rivers are most vulnerable. Damage is caused by flooding, wave impacts, strong currents, erosion, and debris. Even small tsunamis can pose a threat. Local tsunamis are particularly dangerous due to their rapid arrival.
6.2 How Can I Prepare for a Tsunami?
While tsunamis can’t be prevented, preparation can save lives.
- Find out if your home, school, or workplace is in a tsunami hazard zone.
- Educate yourself about tsunami warnings and ensure you have multiple ways to receive official warnings.
- Make an emergency plan, including family communication and evacuation plans.
- Map out routes to safe places on high ground or inland.
- Practice walking your routes.
- Put together a portable disaster supplies kit.
- Share your knowledge and plans with others.
6.3 How Will I Know If a Tsunami Is Coming?
You may receive an official tsunami warning or observe a natural tsunami warning. Natural warnings include strong or long earthquakes, a loud roar from the ocean, and unusual ocean behavior.
6.4 How Should I Respond to a Tsunami Warning?
Your response depends on where you are and the type of warning you receive.
- If you are in a tsunami hazard zone and receive an official tsunami warning, stay out of the water and away from beaches. Get more information and follow evacuation orders.
- If you receive a natural tsunami warning, protect yourself during the earthquake. Take action immediately and move to a safe place.
If you are on the beach or near water and feel an earthquake, move quickly to high ground.
6.5 Who Issues Tsunami Evacuation Orders?
Local emergency management officials typically issue and coordinate evacuation requests/instructions.
6.6 Will I Be Safe From a Tsunami in a Tall Building?
Most buildings are not designed to withstand tsunami impacts. However, the upper stories of some strong and tall buildings may provide protection if no other options are available.
6.7 What Do I Do If I Am in a Boat in a Harbor or at Sea During a Tsunami?
If you are in a harbor and get a tsunami warning, leave your boat and move to a safe place on land. If you are at sea, move to a safe depth (at least 180 feet) and stay away from harbors until officials say the threat has passed.
Knowing how fast do tsunamis travel is only one piece of the puzzle. TRAVELS.EDU.VN encourages everyone in potential tsunami zones to prepare in advance. A family emergency plan and supplies can make all the difference when disaster strikes.
Are you ready to plan your visit to Napa Valley, free of worry? Contact TRAVELS.EDU.VN today at 123 Main St, Napa, CA 94559, United States, via WhatsApp at +1 (707) 257-5400, or visit our website at travels.edu.vn for personalized guidance and support. Let us help you create unforgettable memories while ensuring your safety and peace of mind.
FAQ About Tsunamis
- What is the most common cause of tsunamis?
Large earthquakes below or near the ocean floor are the most common cause. - Can tsunamis be predicted with certainty?
No, scientists cannot predict exactly when and where a tsunami will strike. - How can I receive tsunami warnings?
Through local radio and television, marine radio, wireless emergency alerts, NOAA Weather Radio, and NOAA websites. - What should I do if I am in a tsunami hazard zone and receive an official warning?
Stay out of the water, get more information, and evacuate to a safe place. - What is a natural tsunami warning?
A strong earthquake, a loud roar from the ocean, and unusual ocean behavior. - How high can a tsunami wave get?
Most tsunamis are less than 10 feet high, but can exceed 100 feet in extreme cases. - Are all coastlines equally at risk for tsunamis?
No, coastlines near subduction zones are at a higher risk. - How long can a tsunami last?
Large tsunamis may continue for days in some locations. - What is the difference between a tsunami watch and a tsunami warning?
A watch means a tsunami may later impact the area, while a warning means a tsunami is imminent or expected. - Can weather cause a tsunami?
Yes, certain weather conditions can generate meteotsunamis.
