1. A tsunami is usually caused by an earthquake but can also be caused by a volcanic eruption, landslide, rapid changes in atmospheric pressure, or a meteorite.^b
2. A tsunami is not just one big wave, but a series of waves called a “wave train.” The time period between waves is called the “wave period” and can be between a few minutes and two hours. The first wave is usually not the strongest, and later waves, such as the fifth or sixth, may be significantly larger.^f
3. Greek historian Thucydides (460–395 B.C.) in his History of the Peloponnesian War was the first to associate tsunamis with underwater earthquakes.ⁱ
4. In the deepest part of the ocean, tsunami waves are often only 1 to 3 feet tall. Sailors may not even realize that tsunami waves are passing beneath them.^g
5. The Indonesia 9.0 earthquake in 2004 released more energy than all the earthquakes on the planet in the last 25 years combined. A segment of seafloor the size of the state of California moved upward and seaward by more than 30 feet, displacing huge amounts of water.^f
6. Approximately 99% of all tsunami-related fatalities have occurred within 160 miles (250 km) of the tsunami’s origin or within 30 minutes of when the tsunami was generated. Consequently, anyone in a coastal area who feels a strong earthquake should take that as a natural warning that a tsunami may be imminent and leave low-lying coastal areas.^b
Tsunamis are typically caused by thrust-type subduction-zone earthquakes
7. Earthquake-induced tsunamis are created along subduction zones, or when a lighter tectonic plate is forced above a heavier plate. The sudden rise or fall of the ocean floor displaces the entire overlying water column. This rise and fall of the ocean level above the earthquake generates a tsunami. A tsunami will generally not form if the tectonic plates instead split apart or slide past each other.^f
8. The states in the U.S. at greatest risk for tsunamis are Hawaii, Alaska, Washington, Oregon, and California.^e
9. While no one has witnessed a tsunami caused by a meteorite, many scientists think that a meteorite may have created a tsunami that wiped out life on Earth more than 3.5 billion years ago.^f
10. Scientists believe that an asteroid struck the Indian Ocean about 4,800 years ago. The tsunami that resulted is theorized to have been approximately 600 feet (180 m) high.^f
11. One of the largest earthquakes in history occurred over 100 miles off the coast of Chile on May 22, 1960. Just 15 minutes after the 9.5 quake, 80-foot waves struck the coast. Fifteen hours later, tsunami waves struck Hawaii and, finally, 22 hours after the earthquake, the tsunami struck Japan—10,000 miles from where the earthquake took place.^g
12. While waves generated by wind may travel anywhere from around 2 to 60 miles (3.2 to 97 km) per hour, tsunami waves can travel at speeds of 600 miles (970 km) per hour, the speed of a jet plane.^b
13. The farthest distance inland (horizontally) reached by tsunami waters is referred to as the area of inundation. The highest point (vertically) that this water reaches is called the run-up.^f
14. The Indian Ocean tsunami of 2004 killed more than 216,000 people, possibly as many as 283,000. Victims included not only local people but also approximately 9,000 tourists from Australia, Sweden, the United Kingdom, and the U.S. who were spending their Christmas vacations at beach resorts in Southeast Asia.^g
15. Palm trees with their long, bare trunks are well adapted to life on the shore and often survive tsunamis intact.^g
16. A “mega-tsunami” is a tsunami with extremely high waves and is usually caused by a landslide. A mega-tsunami occurred at Lituya Bay, Alaska, in 1958, creating the tallest tsunami ever recorded at 1,700 feet (534 m) high. Miraculously, only two people died.^f
17. Scientists hypothesize that the next mega-tsunami may occur in the Canary Islands. The mega tsunami could cross the Atlantic Ocean and devastate U.S. coastal cities like New York, Boston, and Miami with waves reaching more than 100 feet high.^f
18. When an enormous earthquake hit Lisbon in 1755, the city’s terrified citizens rushed to the shore for safety. They were amazed to see seawater rushing away from the shore. Minutes later, a tsunami arrived. Ninety thousand residents were killed.^b
Experts suggest evacuating to a place at least 50 feet above sea level during a tsunami
19. Reports show that those who use their cars to escape tsunamis often get stuck in traffic jams or encounter other obstacles and are, therefore, more likely to be swept away. Reports show that the best way to escape is on foot, climbing up any steep slopes nearby as quickly as possible.^b
20. People often die after the first tsunami wave because they return to their homes too soon or go to the beach to help stranded people or animals, only to be engulfed by another tsunami wave.^b
21. If caught by a tsunami wave, it is better not to swim, but rather to grab a floating object and allow the current to carry you.^b
22. Seiches (SAYSH uhz) are like tsunamis, but instead of occurring in seas and oceans, they occur in enclosed bodies of water, such as lakes or inland seas. They are usually smaller and less harmful than tsunamis. Wind is the most common cause of seiches.^j
23. Up to half an hour before a tsunami strikes, the ocean can (but not always) suddenly appear to drain away. The withdraw of the water is called the “drawback” and is the trough of the tsunami reaching the shore.^j
24. Tsunami means “harbor wave” in Japanese (tsu = harbor + nami = wave), reflecting Japan’s tsunami-prone history.^b
25. When a tsunami crashes into coastal areas, it is typically moving at about 22 mph (35 km/hr). The speed as it moves inland changes dramatically depending on the slope of the beach and the shore environment. The force of the tsunami backwash can be just as strong and in some cases stronger than the initial impact.^g
26. The costliest tsunami ever to strike the western United States and Canada occurred on March 28, 1964, when an 8.4 earthquake struck Alaska. Waves reached as high as 21 feet and killed more than 120 people. Damages reached $106 million.^b
27. The state at greatest risk for a tsunami is Hawaii. Hawaii experiences about one tsunami a year and a damaging tsunami every seven years. California, Oregon, and Washington have a damaging tsunami about every 18 years.^b
28. Many who were killed in the 2004 Indian Ocean tsunami were women and children. Many women were reportedly waiting along the beaches for their husbands to return from fishing, and children were simply too weak to fight the strong currents. About one third of the dead were children and, in many locations, four times as many women as men were killed.^f
The 2004 Indian Ocean tsunami uncovered the remains of Mahabalipuram
29. The Indian Ocean tsunami in 2004 uncovered the lost city Mahabalipuram, the capital of a powerful kingdom that traded with China, Roma, Greece, Arabia, and Egypt some 1,500 years ago. It is said that the capital was kodalkol or “swelled by the sea” at the height of its glory.^f
30. Tsunamis can poison fresh-water surface and groundwater systems as well as soil by leaving large amounts of salt behind. Consequently, thousands of people can die of starvation and disease long after the tsunami is gone.^b
31. While tsunamis have been recorded in every ocean on Earth, about 80% of all tsunamis occur in the Pacific “Ring of Fire.”^b
32. Only two large tsunamis are known to have struck Europe: one struck Crete and surrounding Mediterranean coasts in 1530 B.C., and one struck Lisbon, Portugal in 1755.^b
33. A tsunami hits land with thousands of times the power of a regular wave. Regular waves are caused by wind pushing water at the surface of the ocean or other body of water. Tsunami waves are created by an event that affects the entire water column, from the ocean floor to its surface.^e
34. Tsunami waves do not look like normal waves because they do not break and curl as normal waves do. They come as rapid floods of water or in the form of a bore, which is a large, steep wave that looks like a wall of water.ⁱ
Some animals may have the ability to detect impending natural disasters
35. Hours before the Indian Ocean tsunami, people reported seeing elephants and flamingos heading for higher ground. Dogs and zoo animals refused to leave their shelters. After the tsunami, very few dead animals were found.^b
36. As a tsunami wave approaches shallow water near land, it slows down to about 20-30 miles (30-50 km) per hour. As it slows, all the water that had been traveling so fast pulls up, causing the wave to grow higher and higher. By the time it hits shore, a tsunami wave can reach 100 feet high, or as tall as a 10-story building.^f
37. Tsunamis were sometimes called tidal waves, but this is misleading because tsunamis have nothing to do with tides.^b
38. Some geologists suggest the ancient tsunamis are the source of ancient legends, such as the great biblical flood, the parting of the Red Sea during the exodus of the Israelites from Egypt, and the destruction of the Minoan civilization on the island of Crete.^f
39. In the Pacific region, nearly 500,000 people have died from tsunamis over the last 2,000 years. The 2004 Indian Ocean tsunami alone exerted a death toll now estimated at more than 280,000.^f
40. The plural form of the term can be either “tsunami” or “tsunamis.”^f
41. Tsunamis are known from ancient times, dating back almost 4,000 years in China.^b
42. Of the three major oceans, only the Pacific Ocean has an integrated multinational tsunami warning system. There was no tsunami warning system in the Indian Ocean in 2004, though experts had previously recommended one be installed.^f
43. Because of its long history of devastating tsunamis, Japan had the most advanced tsunami warning system in the world prior to the 2011 tsunami, which consisted of more than 1,500 seismometers and more than 500 water-level gauges. Japan’s tsunami warning system costs $20 million a year to run.^e
44. As of March 25 2011, there have been over 21,911 dead and missing in the Japan tsunami (over 10,000 confirmed dead; 17,440 missing) and 2,755 injured.^d
45. The World Bank estimates that rebuilding the tsunami-affected areas of Japan will cost $232 billion and will take at least five years.^a
A 9.0 earthquake 81 miles off the coast of Sendai caused the massive 2011 tsunami
46. The earthquake that caused the 2011 Japan tsunami is the world’s fifth-largest earthquake since 1900. It has been 1,200 years since an earthquake of this magnitude struck the plate boundary of Japan.^c
47. Over 180,000 people were evacuated after an earthquake and tsunami damaged the main cooling systems and generators at the Fukushima Daiichi nuclear complex in Japan in 2011.^a
48. After the 2011 Japan tsunami, a tide of bodies washed ashore on the peninsula in Miyagi Prefecture.^h
49. The 2011 Japan tsunami is estimated to become the world’s most expensive disaster in history.^a
50. Tsunamis retain their energy, meaning they can travel across entire oceans with limited energy loss. A tsunami that travels thousands of miles across the ocean is called a transoceanic tsunami or teletsunami. A tsunami that only reaches the coast near the point of its origin is a local tsunami.^b
    
    History’s Eight Deadliest Tsunamis (not including the 2011 Japan tsunami) ^b

    Location	Date	Fatalities
    1. Indian Ocean	2004	225,000+
    2. Crete-Santorini, Ancient Greece	1410 B.C.	100,000
    3. Portugal-Morocco	1755	60,000
    4. South Sea China	1782	40,000
    5. Krakatau, Indonesia	1883	36,5000
    6. Tokaido-Nankaido, Japan	1707	30,000
    7. Sanriku, Japan	1896	26,360
    8. Northern Chile	1868	25,674

    
    
    Casualties from the December 26, 2004, Indian Ocean Tsunami ^e

    Country	Deaths	Missing	Injured	Displaced
    Indonesia	167,736	37,063	--	> 500,000
    Sri Lanka	35,322	6,700	21,411	516,150
    India	18,045	5,640	--	647,599
    Thailand	8,212	2,817	8,457	7,000
    Somalia	289	211	--	5,000
    Myanmar	500	500	45	3,200
    Maldives	108	26	--	15,000
    Malaysia	75	6	299	--
    Tanzania	13	--	--	--
    Seychelles	3	--	57	200
    Bangladesh	2	--	--	--
    South Africa	2	--	--	--
    Kenya	1	--	2	--
    Madagascar	> 200	--	--	1,000
    Total	230,00	45,752	125,000	1,690,000

    
    

-- Posted March 26, 2011

References

^a Albon, Christopher. “Japan Earthquake and Tsunami Facts and Figures.” UN Dispatch. March 22, 2011. Accessed: March 24, 2011.

^b Fine, Jil. 2007. Tsunamis. New York: Scholastic. 

^c Foster, Malcom. “Hundreds Killed in Tsunami after 8.9 Japanese Quake.” The Denver Post. March 11, 2011. Accessed: March 24, 2011.

^d “Japan Tsunami Tops 10,000 Two Weeks after Quake.” BBCNews. March 25, 2011. Accessed: March 25, 2011.

^e Refern, Martin. 2003. The Earth: A Very Short Introduction. New York: Oxford University Press.

^f Kuskuy, Timothy, Ph.D. 2008. Tsunamis: Great Waves from the Sea. New York: Infobase Publishing.

^g Smith, Craig B. 2006. Extreme Waves. Washington D.C.: Joseph Henry Press.

^h “Tide of Bodies Overwhelms Japan.” News24. March 11, 2011. Accessed: March 24, 2011.

ⁱ Thucydides. 2009. The Peloponnesian War. Martin Hammond, trans. Peter John Rhodes, ed. New York: Oxford University Press.